EP1953739A2 - Method and device for reducing noise - Google Patents

Method and device for reducing noise Download PDF

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Publication number
EP1953739A2
EP1953739A2 EP08008031A EP08008031A EP1953739A2 EP 1953739 A2 EP1953739 A2 EP 1953739A2 EP 08008031 A EP08008031 A EP 08008031A EP 08008031 A EP08008031 A EP 08008031A EP 1953739 A2 EP1953739 A2 EP 1953739A2
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EP
European Patent Office
Prior art keywords
celp
tdac
decoded signal
env
contribution
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EP08008031A
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German (de)
French (fr)
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EP1953739A3 (en
EP1953739B1 (en
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Martin Gartner
Stefan Schandl
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Siemens AG
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Siemens AG
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Priority claimed from DE102005019863A external-priority patent/DE102005019863A1/en
Priority claimed from DE200510032079 external-priority patent/DE102005032079A1/en
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    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10L—SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING
    • G10L21/00—Speech or voice signal processing techniques to produce another audible or non-audible signal, e.g. visual or tactile, in order to modify its quality or its intelligibility
    • G10L21/02—Speech enhancement, e.g. noise reduction or echo cancellation
    • G10L21/0208—Noise filtering
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10L—SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING
    • G10L19/00—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis
    • G10L19/02—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis using spectral analysis, e.g. transform vocoders or subband vocoders
    • G10L19/022—Blocking, i.e. grouping of samples in time; Choice of analysis windows; Overlap factoring
    • G10L19/025—Detection of transients or attacks for time/frequency resolution switching
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10L—SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING
    • G10L19/00—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis
    • G10L19/04—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis using predictive techniques
    • G10L19/08—Determination or coding of the excitation function; Determination or coding of the long-term prediction parameters
    • G10L19/12—Determination or coding of the excitation function; Determination or coding of the long-term prediction parameters the excitation function being a code excitation, e.g. in code excited linear prediction [CELP] vocoders
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10L—SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING
    • G10L19/00—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis
    • G10L19/04—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis using predictive techniques
    • G10L19/16—Vocoder architecture
    • G10L19/18—Vocoders using multiple modes
    • G10L19/24—Variable rate codecs, e.g. for generating different qualities using a scalable representation such as hierarchical encoding or layered encoding
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10L—SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING
    • G10L21/00—Speech or voice signal processing techniques to produce another audible or non-audible signal, e.g. visual or tactile, in order to modify its quality or its intelligibility
    • G10L21/02—Speech enhancement, e.g. noise reduction or echo cancellation
    • G10L21/0316—Speech enhancement, e.g. noise reduction or echo cancellation by changing the amplitude
    • G10L21/0364—Speech enhancement, e.g. noise reduction or echo cancellation by changing the amplitude for improving intelligibility

Definitions

  • the invention relates to a method for decoding a signal which has been coded by means of a hybrid coder.
  • the invention further relates to a correspondingly configured device for decoding.
  • CELP Code Excited Linear Prediction
  • CELP works in the time domain and is based on an excitation model for a variable filter. In this case, the speech signal is represented both by filter parameters and by parameters which describe the excitation signal.
  • the corresponding decoder is also used, which can decrypt or decode the coded data.
  • Corresponding communication devices have such a so-called codec in order to be able to send and receive data, which is necessary for a communication.
  • perceptual codecs coder / decoder
  • codec coder / decoder
  • These perceptual codecs are based on information reduction in the frequency domain and use masking effects of the human hearing system, ie that, for example, certain frequencies or changes that the human being can not perceive are not displayed either. This reduces the complexity of the coder or codec. Since these coders usually work with a transformation of the time signal into the frequency domain, wherein the transformation is carried out, for example, by means of MDCT (Modified Discrete Cosine Transformation), these are often also referred to as transform coders or codecs. This term will be used in the further application.
  • MDCT Modified Discrete Cosine Transformation
  • Scalable codecs are those codecs that initially produce excellent audio quality at a relatively high bit rate of the encoded data stream. This results in relatively long, periodically transmitted packets.
  • a packet is a plurality of data that accumulate in a time interval and are transmitted together in that packet. For packets, often important data is transmitted first and less important data is subsequently transmitted. With these long packets, however, it is possible to shorten these packets by removing part of the data, in particular by truncating the last transmitted part of the packet. This goes hand in hand with a deterioration in quality.
  • scalable codecs may want to work at low bit rates with CELP codecs and higher bit rates with transform codecs. This has led to the development of hybrid CELP / Transform codecs which encode a good quality base signal according to the CELP method and, in addition, generate an additional signal according to the Transformcodec method, with which the base signal is improved. This then leads to the desired excellent quality.
  • a disadvantage of using these Transformcodecs is that a so-called "pre-echo effect" occurs.
  • This is a noise that is evenly distributed over the entire block length of a Transform-Coder block.
  • a block is understood to mean a set of data which is coded together.
  • a typical block length is 40 msec.
  • the noise of the PreEcho effect is caused by quantization errors of transmitted spectral components. With a uniform signal level, the level of this noise is everywhere below the level of the useful signal. However, if you have a useful signal with a zero level followed by a sudden high level, so this noise is clearly heard before the onset of high level.
  • a well-known example of this in the literature is the signal course when a Castanette rattles.
  • the associated energy envelope is determined from the two decoded signal contributions.
  • energy envelope is meant in particular the energy curve of a signal over time.
  • a key figure is formed, for example, a ratio.
  • This figure again serves to derive a gain factor.
  • This method has particular advantages when energy is e.g. in the coding method, which leads to the first decoded signal contribution, is detected more reliably. In that case, a deviation can be detected by the characteristic number or the amplification factor.
  • the second decoded signal contribution can be multiplied by the gain factor. Thereby, the above-mentioned deviation can be corrected.
  • All signals can be subdivided into time segments, wherein in particular the time segments which are used for the first decoded signal contribution can be shorter than those for the second one.
  • the first signal contribution may be from a CELP decoder which decodes a CELP coded signal, the second from a transform decoder which decodes a transform coded signal.
  • this transform-coded signal may also contain the first CELP-decoded signal contribution, which has been transform-coded after the decoding, added to the transform-coded signal transmitted by the transmitter (ie already in the frequency domain), and then decoded in the transform decoder as a contribution to the second signal contribution ,
  • a summation of the transmitted CELP-coded signal and the transmitted transform-coded signal can also take place in the time domain.
  • the amplification factor may in particular be equal to the characteristic number. Then, when a suitable ratio is formed, a corresponding weakening of the second decoded signal contribution may result if this primarily contains the pre-echo noise.
  • the first decoder may be based on the CELP technology or / and the second coder may be a transform decoder. This results in a particularly effective noise reduction at the same time excellent quality of the decoded signal.
  • the change of the received total signal on the decoder side can be made in particular only if certain criteria are present.
  • a method in which, based on the method explained, the decoded signal or its first and second decoded signal contributions are treated separately according to frequency ranges.
  • This has the following advantage.
  • the desired energy for these frequency bands is known for a plurality of frequency bands, namely from the energy of the individual first decoded signal contributions separated by frequency ranges, for example CELP signals.
  • an add-on signal (additional contribution) can now be provided, which, however, can deviate considerably in its energy. Particularly problematic is when the energy of the second decoded signal contribution is significantly too high, e.g. due to pre-echo effects.
  • the method now introduces for each individually treated frequency band a limitation of the energy (or the level) of the second signal contribution as a function of the energy of the first signal contribution. This method is the more effective, the more frequency bands are treated separately in this way.
  • FIG. 1 the schematic flow of a coding and decoding process is shown by means of an embodiment.
  • an analogue signal S to be transmitted to a receiver is preprocessed or preprocessed for the coding by means of a preprocessing device PP, for example by being digitized.
  • a decomposition of the signal into time segments or frames in a subdivision unit F takes place.
  • a signal prepared in this way is supplied to a coding unit COD.
  • the coding unit COD comprises a hybrid coder comprising a first coder, a CELP coder COD1 and a second coder, a transform coder COD2.
  • the CELP coder COD1 comprises a plurality of CELP coders COD1_A, COD1_B, COD1_C, which operate in different frequency ranges. Through this division into different frequency ranges a particularly accurate coding can be guaranteed. Furthermore, this division into different frequency ranges very well supports the concept of a scalable codec, since depending on the desired scaling only one, several or all frequency ranges can be transmitted.
  • the CELP coder COD1 delivers a basic contribution S_G to the coded total signal S_GES.
  • the transform coder COD2 provides an additional contribution S_Z to the coded total signal S_GES.
  • the coded total signal S_GES is transmitted by means of a communication device KC on the coder side C to a communication device KD on a decoder side D.
  • a processing for example, a splitting of the coded total signal into the contributions S_G and S_Z
  • a processing for example, a splitting of the coded total signal into the contributions S_G and S_Z
  • a processing device PROC takes place, wherein subsequently the processed data or the processed signal of a decoding device DEC for subsequent decoding DEC transferred (see also the Figures 3 and 4 ).
  • the decoding is followed by a noise reduction in a noise reduction device NR, which in FIG. 3 is shown in greater detail.
  • FIG. 2 is a first communication device COM1 (for example, representing the components on the encoder side C of FIG. 1 ), which has a transmitting and receiving unit ANT1 (for example, corresponding to the communication device KC) for transmitting and / or receiving data, as well as a computing unit CPU1, which for the realization of the components on the encoder side C or for performing the in FIG. 1 illustrated encoding method (processing on the encoder side C) is set up.
  • the transmission of data by means of the transmitting / receiving unit ANT1 via a communication network CN (which, for example, depending on the communication devices to be used as the Internet, a telephone network or mobile network can be set up).
  • a communication network CN which, for example, depending on the communication devices to be used as the Internet, a telephone network or mobile network can be set up).
  • the reception is performed by a second communication device COM2 (for example, representing the components on the right side of FIG. 1 ), which in turn has a transmitting and receiving unit ANT2 (for example, corresponding to the communication device KB), and a computing unit CPU2, which for the realization of the components on the decoder side D or for performing a decoding method (processing on the decoder side D) FIG. 1 is set up.
  • a second communication device COM2 for example, representing the components on the right side of FIG. 1
  • ANT2 for example, corresponding to the communication device KB
  • CPU2 for the realization of the components on the decoder side D or for performing a decoding method (processing on the decoder side D) FIG. 1 is set up.
  • Examples of possible implementations of the communication devices COM1 and COM2 in which this method can be used are IP telephones, voice gateways or mobile telephones.
  • a CELP coded signal S_COD, CELP (corresponding to the signal S_G) is decoded by means of a full-band CELP decoder DEC_GES, CELP.
  • the decoded signal S_CELP is forwarded, on the one hand, to a (first) energy envelope determination unit GE1 for determining the associated envelope ENV_CELP, and, on the other hand, to a time domain aliasing cancellation (TDAC) encoder COD_TDAC.
  • TDAC time domain aliasing cancellation
  • the coded signal S_COD, CELP, TDAC, together with the receiver-side derived transform coded signal S_COD, TDAC (corresponding to the signal S_Z) are routed to a transform decoder DEC_TDAC to produce a decoded signal S_TDAC.
  • the associated energy envelope ENV_TDAC is likewise determined from this decoded signal S_TDAC in a (second) energy envelope determination unit GE2.
  • the ratio R of the energy envelopes to each other as a measure is determined in portions.
  • the energy or the level of this signal contribution can be moved to the more reliable value of the CELP decoded signal S_CELP, so that the final Signal S_out noise is reduced.
  • FIG. 4 Reference is made to explain a further embodiment for reducing the pre-echo effect.
  • CELP codec there are multiple (CELP or other) codecs separated by frequency ranges.
  • FIG. 4 the embodiment shown corresponds to that in FIG. 3 shown embodiment and is an extension in this regard that the in FIG. 3 is not applied to the overall signals from CELP (or other) decoder and transform decoder, but that the method is applied separately to frequency ranges. That is, there is first a division of the total signal or the individual signal contributions to frequency ranges instead, the method of FIG. 3 then per frequency range can be applied to the individual signal contributions.
  • the desired energy for these frequency bands is known for a plurality of frequency bands, namely from the energy of the individual CELP signals separated according to frequency ranges.
  • the Transform Decoder now provides an add-on signal (additional contribution), which, however, can differ considerably in its energy. Particularly problematic is when the energy of the signal from the transform decoder is significantly too high, e.g. due to pre-echo effects.
  • the method now introduces a limit on the Transformcodec energy depending on the CELP energy for each individually treated frequency band. This method is the more effective, the more frequency bands are treated separately in this way.
  • the total signal consists of a 2000 Hz sound, which comes entirely from the CELP codec portion.
  • the Transformcodec now provides an interference signal with a frequency of 6000 Hz; the energy of the interfering signal is 10% of the energy of the 2000 Hz tone.
  • the criterion for limiting the Transformcodec share is that this max. the same size as the CELP share may be.
  • Case 1 No splitting is made after frequency bands (first embodiment): Then the 6000 Hz interference signal is not suppressed since it has only 10% of the energy of the 2000 Hz tone from the CELP codec.
  • Case 2 The frequency bands A: 0 - 4000 Hz and B: 4000 Hz - 8000 Hz are treated separately (further embodiment): In this case, the interference signal is completely suppressed because in the upper frequency band, the CELP component is zero, and thus also the Transformcodecsignal is limited to the value zero.
  • FIG. 4 is now (corresponding to FIG. 3 ) again to see a decoding device DEC and a noise reduction device NR with the essential components for the schematic representation of the sequence of a level adjustment or pre-echo reduction.
  • DEC decoding device
  • NR noise reduction device
  • a CELP coded signal S_COD, CELP (corresponding to the signal contribution S_G) is decoded by means of a whole-band CELP decoder DEC_GES, CELP '.
  • the total band CELP decoder comprises two decoding devices, a first decoder DEC_FB_A for decoding the signal S_COD, CELP in a first frequency band A and a second decoding device DEC_FB_B for decoding the signal S_COD, CELP in a second frequency band B.
  • a first decoded signal S_CELP_A is passed to a (first) energy envelope determination unit GE1_A for determining the associated envelope ENV_CELP_A, while a second decoded signal S_CELP_B is sent to a (second) energy envelope determination unit GE1_B for determining the associated envelope ENV_CELP_B becomes.
  • a receiver-side derived transform coded signal S_COD, TDAC (corresponding to the signal S_Z) is passed to a transform decoder DEC_TDAC to produce a decoded signal S_TDAC, which in turn is applied to a frequency band splitter (frequency band splitter) FBS.
  • the division into frequency bands can optionally also take place in the frequency domain, before the inverse transformation into the time domain. This eliminates in particular the delay associated with a frequency band splitter operating in the time domain (high, low, or bandpass filter).
  • the associated energy envelope ENV_TDAC_A or ENV_TDAC_B is also determined in a (third) energy envelope determination unit GE2_A or a (fourth) energy envelope determination unit GE2_B.
  • a gain factor (or attenuation factor, since the gain is negative) G_A is determined for the frequency band A, while in a second gain determination unit BD_B for the frequency band B, a gain factor is calculated using the energy envelopes ENV_CELP_B and ENV_TDAC_B (Damping factor) G_B is determined.
  • the determination of the respective amplification factors can according to the provision of FIG. 3 (see components D, BFE).
  • a respective amplification factor G_A or G_B can be set to "1", so that when a multiplication occurs, a respective frequency band-dependent signal S_TDAC_A or S_TDAC_B remains unchanged.
  • amplification factor G_A is multiplied by the signal S_TDAC_A and the amplification factor G_B is multiplied by the signal S_TDAC_B.
  • the multiplied (possibly attenuated) frequency band dependent signals are combined to produce a final noise reduced (total frequency) signal S_OUT '.

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Abstract

A noise suppression process comprising a first decoded signal portion (S CELP) and a second decoded signal portion (S TDAC) which involves determining a first energy envelope generating curve (ENV CELP) and a second energy envelope generating curve (ENV TDAC) of the first signal portion and of the second decoded signal portion. The process then involves forming an identification number (R) depending on a comparison of the first and second energy envelope generating curves, deriving an amplification factor (G) which depends on the identification number. An independent claim is also included for the device e.g. communication equipment.

Description

Die Erfindung betrifft ein Verfahren zur Decodierung eines Signals, welches mittels eines Hybridcodierers codiert wurde. Die Erfindung betrifft ferner eine entsprechend ausgestaltete Vorrichtung zur Decodierung.The invention relates to a method for decoding a signal which has been coded by means of a hybrid coder. The invention further relates to a correspondingly configured device for decoding.

Zur Codierung von Audiosignalen haben sich unterschiedliche Verfahren als besonders effektiv herausgestellt. So hat sich beispielsweise zur qualitativ guten Codierung von Sprachsignalen, welche eine gute Qualität aufweisen, und bei gleichzeitig niedrigen Bitraten des codierten Datenstroms insbesondere die sogenannte CELP Technologie (Code Excited Linear Prediction) als günstig erwiesen. CELP arbeitet im Zeitbereich und basiert auf einem Anregungsmodell für ein variables Filter. Hierbei wird das Sprachsignal sowohl durch Filterparameter als auch durch Parameter, welche das Anregungssignal beschreiben, dargestellt.For the coding of audio signals, different methods have proven to be particularly effective. Thus, for example, the so-called CELP technology (Code Excited Linear Prediction) has proved to be favorable for the high-quality coding of speech signals which have a good quality, and at the same time low bit rates of the encoded data stream. CELP works in the time domain and is based on an excitation model for a variable filter. In this case, the speech signal is represented both by filter parameters and by parameters which describe the excitation signal.

Zumeist wird in Hinblick auf Codierer auch von dem entsprechenden Decodierer gesprochen, der die codierten Daten wieder entschlüsseln bzw. decodieren kann. Entsprechende Kommunikationsgeräte weisen einen solchen sogenannten Codec auf, um eben Daten versenden und empfangen zu können, was für eine Kommunikation erforderlich ist.In most cases, with regard to coders, the corresponding decoder is also used, which can decrypt or decode the coded data. Corresponding communication devices have such a so-called codec in order to be able to send and receive data, which is necessary for a communication.

Für die Codierung von Musik- und Sprachsignalen, welche eine sehr hohe Qualität insbesondere auch bei höheren Bitraten des codierten Datenstroms aufweisen sollen, haben sich vor allem sogenannte perceptuelle Codecs (Codec = Codierer/Decodierer) durchgesetzt. Diese perceptuellen Codecs basieren auf einer Informationsreduktion im Frequenzbereich und sie nutzen Maskierungseffekte des menschlichen Hörsystems aus, d.h., dass beispielsweise bestimmte Frequenzen oder Änderungen, die der Mensch nicht wahrnehmen kann, auch nicht dargestellt werden. Dadurch wird die Komplexität des Coders oder Codecs gesenkt. Da diese Coder meist mit einer Transformierung des Zeitsignals in den Frequenzbereich arbeiten, wobei die Transformierung beispielsweise mittels MDCT (Modified Discrete Cosine Transformation) vorgenommen wird, werden diese oft auch als Transformcoder oder -codecs bezeichnet. Dieser Ausdruck wird im Rahmen der weiteren Anmeldung verwendet.For the coding of music and speech signals, which should have a very high quality especially at higher bit rates of the coded data stream, especially so-called perceptual codecs (codec = coder / decoder) have prevailed. These perceptual codecs are based on information reduction in the frequency domain and use masking effects of the human hearing system, ie that, for example, certain frequencies or changes that the human being can not perceive are not displayed either. This reduces the complexity of the coder or codec. Since these coders usually work with a transformation of the time signal into the frequency domain, wherein the transformation is carried out, for example, by means of MDCT (Modified Discrete Cosine Transformation), these are often also referred to as transform coders or codecs. This term will be used in the further application.

In letzter Zeit kommen zunehmend sogenannte skalierbare Codecs zum Einsatz. Skalierbare Codecs sind solche Codecs, die zunächst eine exzellente Audioqualität bei relativ hoher Bitrate des codierten Datenstroms erzeugen. Damit ergeben sich relativ lange, periodisch zu übertragende Pakete.Recently, so-called scalable codecs are increasingly being used. Scalable codecs are those codecs that initially produce excellent audio quality at a relatively high bit rate of the encoded data stream. This results in relatively long, periodically transmitted packets.

Ein Paket ist eine Mehrzahl Daten, welche in einem Zeitintervall anfallen, und zusammen eben in diesem Paket übertragen werden. Bei Paketen werden oftmals wichtige Daten zuerst und weniger wichtige Daten nachfolgend übertragen. Bei diesen langen Paketen besteht jedoch die Möglichkeit, diese Pakete zu kürzen, indem ein Teil der Daten entfernt wird, insbesondere indem der zeitlich zuletzt übertragene Teil des Paketes abgeschnitten wird. Damit geht natürlich eine Verschlechterung der Qualität einher.A packet is a plurality of data that accumulate in a time interval and are transmitted together in that packet. For packets, often important data is transmitted first and less important data is subsequently transmitted. With these long packets, however, it is possible to shorten these packets by removing part of the data, in particular by truncating the last transmitted part of the packet. This goes hand in hand with a deterioration in quality.

Wegen der zuvor genannten Eigenschaften bietet es sich für skalierbare Codecs an, bei niedrigen Bitraten mit CELP Codecs zu arbeiten und bei höheren Bitraten mit Transformcodecs. Dies hat zur Entwicklung von hybriden CELP/Transformcodecs geführt, die ein Basissignal mit guter Qualität nach dem CELP Verfahren codieren und zusätzlich dazu ein Zusatzsignal nach dem Transformcodec-Verfahren generieren, mit dem das Basissignal verbessert wird. Dies führt dann zu der erwünschten exzellenten Qualität.Because of the aforementioned features, scalable codecs may want to work at low bit rates with CELP codecs and higher bit rates with transform codecs. This has led to the development of hybrid CELP / Transform codecs which encode a good quality base signal according to the CELP method and, in addition, generate an additional signal according to the Transformcodec method, with which the base signal is improved. This then leads to the desired excellent quality.

Nachteilig bei der Verwendung dieser Transformcodecs ist, dass ein sogenannter "Pre-Echo Effekt" auftritt. Dabei handelt es sich um ein Störgeräusch, das gleichmäßig über die gesamte Blocklänge eines Transform-Coder Blocks verteilt ist. Unter einem Block versteht man, eine Gesamtheit von Daten, welche gemeinsam codiert werden. Für Transformcodecs beträgt eine typische Blocklänge 40 msec. Das Störgeräusch des PreEcho Effekts entsteht durch Quantisierungsfehler von übertragenen spektralen Komponenten. Bei gleichmäßigem Signalpegel liegt der Pegel dieses Störgeräusches überall unter dem Pegel des Nutzsignals. Hat man allerdings ein Nutzsignal mit einem Null-Pegel gefolgt von einem plötzlichen hohen Pegel, so ist dieses Störgeräusch vor dem Einsetzen des hohen Pegels deutlich zu hören. In der Literatur ist ein bekanntes Beispiel hierfür der Signalverlauf beim Klappern einer Castanette.A disadvantage of using these Transformcodecs is that a so-called "pre-echo effect" occurs. This is a noise that is evenly distributed over the entire block length of a Transform-Coder block. A block is understood to mean a set of data which is coded together. For transform codecs, a typical block length is 40 msec. The noise of the PreEcho effect is caused by quantization errors of transmitted spectral components. With a uniform signal level, the level of this noise is everywhere below the level of the useful signal. However, if you have a useful signal with a zero level followed by a sudden high level, so this noise is clearly heard before the onset of high level. A well-known example of this in the literature is the signal course when a Castanette rattles.

Zur Reduktion dieses Effekts werden bereits verschiedene Verfahren angewandt. Diese arbeiten aber alle mit der Übertragung von Zusatzinformationen, was wiederum das Coderdesign sehr komplex gestaltet oder erzwingt, dass die Coder mit vorübergehend erhöhten Bitraten arbeiten müssen.Various methods are already used to reduce this effect. However, these all work with the transmission of additional information, which in turn makes the coder design very complex or forces the coders to have to work with temporarily increased bit rates.

Ausgehend von diesem Stand der Technik ist es Aufgabe der vorliegenden Erfindung, eine einfache Möglichkeit zu schaffen, eine Störgeräuschreduktion bei mittels eines hybriden Coders codierten Signalen herbeizuführen, bei der keine Zusatzinformation benötigt wird.Based on this prior art, it is an object of the present invention to provide a simple way to bring about a noise reduction in coded by means of a hybrid coder signals, in which no additional information is needed.

Diese Aufgabe wird durch den Gegenstand der unabhängigen Ansprüche gelöst. Vorteilhafte Weiterbildungen sind Gegenstand der abhängigen Ansprüche.This object is solved by the subject matter of the independent claims. Advantageous developments are the subject of the dependent claims.

Für diese Störgeräuschreduktion bei einem decodierten Signal, das sich aus einem ersten, z.B. von einem CELP Decodierer stammenden, und einem zweiten, z.B. von einem TransformDecodierer stammenden Signal zusammensetzt, werden folgende Schritte durchgeführt:For this noise reduction in a decoded signal resulting from a first, e.g. from a CELP decoder, and a second, e.g. composed of a transform decoder, the following steps are performed:

Aus den beiden decodierten Signalbeiträgen wird jeweils die zugehörige Energiehüllkurve ermittelt. Unter Energiehüllkurve versteht man insbesondere den Energieverlauf eines Signals gegenüber der Zeit.The associated energy envelope is determined from the two decoded signal contributions. By energy envelope is meant in particular the energy curve of a signal over time.

Aus einem Vergleich beider Hüllkurven wird eine Kennzahl gebildet, beispielsweise ein Verhältnis.From a comparison of both envelopes a key figure is formed, for example, a ratio.

Diese Kennzahl dient wiederum zum Ableiten eines Verstärkungsfaktors.This figure again serves to derive a gain factor.

Dieses Verfahren weist insbesondere Vorteile auf, wenn Energie z.B. bei dem Codierverfahren, welches zum ersten decodierten Signalbeitrag führt, zuverlässiger erkannt wird. Dann kann nämlich durch die Kennzahl oder den Verstärkungsfaktor eine Abweichung erkannt werden.This method has particular advantages when energy is e.g. in the coding method, which leads to the first decoded signal contribution, is detected more reliably. In that case, a deviation can be detected by the characteristic number or the amplification factor.

Insbesondere kann der zweite decodierte Signalbeitrag mit dem Verstärkungsfaktor multipliziert werden. Dadurch kann die oben erwähnte Abweichung korrigiert werden.In particular, the second decoded signal contribution can be multiplied by the gain factor. Thereby, the above-mentioned deviation can be corrected.

Sämtliche Signale können in Zeitabschnitte unterteilt sein, wobei insbesondere die Zeitabschnitte, welche für den ersten decodierten Signalbeitrag verwendet werden, kürzer sein können als diejenigen für den zweiten.All signals can be subdivided into time segments, wherein in particular the time segments which are used for the first decoded signal contribution can be shorter than those for the second one.

Damit können aufgrund der höheren Zeitauflösung Energieabweichungen im zweiten Signalbeitrag besser korrigiert werden.Thus, due to the higher time resolution, energy deviations in the second signal contribution can be better corrected.

Der erste Signalbeitrag kann aus einem CELP Decodierer stammen, der ein CELP codiertes Signal decodiert, der zweite aus einem Transformdecodierer, der ein transformcodiertes Signal decodiert. Dieses transformcodierte Signal kann insbesondere auch den ersten, CELP-decodierten Signalbeitrag enthalten, der nach der Decodierung transform-codiert wurde, zum vom Sender übertragenen transformcodierten Signal addiert wurde (also schon im Frequenzbereich), und dann im Transformdecodierer als Beitrag zum zweiten Signalbeitrag decodiert wird.The first signal contribution may be from a CELP decoder which decodes a CELP coded signal, the second from a transform decoder which decodes a transform coded signal. In particular, this transform-coded signal may also contain the first CELP-decoded signal contribution, which has been transform-coded after the decoding, added to the transform-coded signal transmitted by the transmitter (ie already in the frequency domain), and then decoded in the transform decoder as a contribution to the second signal contribution ,

Alternativ hierzu kann eine Summenbildung aus dem übertagenen CELP-codierten Signal und dem übertragenen transformcodierten-Signal auch im Zeitbereich erfolgen.Alternatively, a summation of the transmitted CELP-coded signal and the transmitted transform-coded signal can also take place in the time domain.

Der Verstärkungsfaktor kann insbesondere gleich der Kennzahl sein. Dann kann sich bei Bildung eines geeigneten Verhältnisses einen entsprechende Schwächung des zweiten decodierten Signalbeitrages ergeben, wenn dieses vornehmlich das Pre-Echo noise enthält.The amplification factor may in particular be equal to the characteristic number. Then, when a suitable ratio is formed, a corresponding weakening of the second decoded signal contribution may result if this primarily contains the pre-echo noise.

Insbesondere kann es sich bei dem ersten Decoder um einen auf der CELP-Technologie basierenden, oder/und bei dem zweiten Coder um einen Transformdecoder handeln. Damit ergibt sich eine besonders effektive Geräuschreduktion bei gleichzeitig exzellenter Qualität des decodierten Signals.In particular, the first decoder may be based on the CELP technology or / and the second coder may be a transform decoder. This results in a particularly effective noise reduction at the same time excellent quality of the decoded signal.

Die Veränderung des empfangenen Gesamtsignals auf Decoderseite kann insbesondere nur dann vorgenommen werden, wenn bestimmte Kriterien vorliegen.The change of the received total signal on the decoder side can be made in particular only if certain criteria are present.

Insbesondere ist es vorgesehen, dass das Verändern des empfangenen Gesamtsignals auf Decoderseite nur erfolgt, wenn die Signalpegeländerung eine bestimmte Schwelle übersteigt. Dies ermöglicht eine besonders effektive Pre-Echo-Reduktion, da der Pre-Echo-Effekt - wie bereits dargelegt- hauptsächlich bei Pegeländerungen auftritt, da dann das Pre-Echo Geräusch überhalb des Signalpegels liegt. Andererseits wird durch dieses selektive Verändern nicht unnötigerweise auf die Qualitätsverbesserung durch den zweiten Coder verzichtet.In particular, it is provided that changing the received total signal on the decoder side only occurs when the signal level change exceeds a certain threshold. This allows a particularly effective pre-echo reduction, since the pre-echo effect - as already explained - mainly occurs with level changes, since then the pre-echo noise is above the signal level. On the other hand, this selective modification does not unnecessarily dispense with the quality improvement by the second coder.

Gemäß einem weiteren Aspekt der Erfindung wird ein Verfahren geschaffen, bei dem aufbauend auf dem erläuterten Verfahren das decodierte Signal bzw. dessen erste und zweite decodierte Signalbeiträge nach Frequenzbereichen getrennt behandelt werden. Dies hat folgenden Vorteil. Beim Decodieren ist für mehrere Frequenzbänder die Sollenergie für diese Frequenzbändern bekannt, nämlich aus der Energie der einzelnen nach Frequenzbereichen getrennten ersten decodierten Signalbeiträge, beispielsweise CELP-Signale. Durch den zweiten decodierten Signalbeitrag kann nun ein Add-on Signal (Zusatzbeitrag) bereitgestellt werden, welches jedoch in seiner Energie erheblich abweichen kann. Problematisch ist vor allem, wenn die Energie des zweiten decodierten Signalbeitrags erheblich zu hoch ist, z.B. aufgrund von Pre-Echo-Effekten. Das Verfahren führt nun für jedes einzeln behandelte Frequenzband eine Begrenzung der Energie (bzw. des Pegels) des zweiten Signalbeitrags abhängig von der Energie des ersten Signalbeitrags ein. Dieses Verfahren ist umso effektiver, je mehr Frequenzbänder auf diese Weise getrennt behandelt werden.According to a further aspect of the invention, a method is provided in which, based on the method explained, the decoded signal or its first and second decoded signal contributions are treated separately according to frequency ranges. This has the following advantage. During decoding, the desired energy for these frequency bands is known for a plurality of frequency bands, namely from the energy of the individual first decoded signal contributions separated by frequency ranges, for example CELP signals. By the second decoded signal contribution, an add-on signal (additional contribution) can now be provided, which, however, can deviate considerably in its energy. Particularly problematic is when the energy of the second decoded signal contribution is significantly too high, e.g. due to pre-echo effects. The method now introduces for each individually treated frequency band a limitation of the energy (or the level) of the second signal contribution as a function of the energy of the first signal contribution. This method is the more effective, the more frequency bands are treated separately in this way.

Weitere Vorteile der Erfindung werden anhand beispielhafter Ausführungsformen dargestellt.Further advantages of the invention will be illustrated by way of exemplary embodiments.

Es zeigen:

Figur 1
eine Darstellung der wesentlichen Komponenten auf einer Codiererseite und einer Decodiererseite zur Erläuterung des beispielhaften Ablaufs eines Codierungs/Decodierungsvorganges;
Figur 2
eine schematische Darstellung einer Kommunikationsanordnung zur Übertragung eines codierten Signals zwischen Kommunikationsgeräten über ein Kommunikationsnetz;
Figur 3
eine Decodiereinrichtung bzw. eine Geräuschunterdrückungseinrichtung zur Erläuterung der Reduktion von Pre-Echos mit Hilfe von Gain-Adaption, welche auf einem CELP Signal basiert;
Figur 4
eine weitere Ausführungsform zur Pegelanpassung bzw. zur Reduktion von Pre-Echos.
Show it:
FIG. 1
a representation of the essential components on an encoder side and a decoder side for explaining the exemplary sequence of a coding / decoding process;
FIG. 2
a schematic representation of a communication arrangement for transmitting a coded signal between communication devices via a communication network;
FIG. 3
a decoding device for explaining the reduction of pre-echoes with the aid of gain adaptation, which is based on a CELP signal;
FIG. 4
a further embodiment for level matching or for the reduction of pre-echoes.

In FIG 1 ist der schematische Ablauf eines Codierungs- und Decodierungsvorgang anhand einer Ausführungsführungsform gezeigt. Auf einer Codiererseite C wird ein analoges an einen Empfänger zu übertragendes Signal S mittels einer Vorverarbeitungseinrichtung PP für die Codierung vorverarbeitet bzw. vorbereitet, beispielsweise indem es digitalisiert wird. Es erfolgt weiterhin eine Zerlegung des Signals in Zeitabschnitte bzw. Rahmen in einer Unterteilungseinheit F. Ein derart vorbereitetes Signal wird einer Codierungseinheit COD zugeführt. Die Codierungseinheit COD weist einen hybriden Coder auf, der einen ersten Coder, einen CELP-Coder COD1 und einen zweiten Coder, einen Transformcoder COD2 umfasst. Der CELP-Coder COD1 umfasst eine Mehrzahl von CELP-Codern COD1_A, COD1_B, COD1_C, welche in unterschiedlichen Frequenzbereichen arbeiten. Durch diese Aufteilung in unterschiedliche Frequenzbereiche kann eine besonders akkurate Codierung gewährleistet werden. Ferner unterstützt diese Aufteilung in unterschiedliche Frequenzbereiche sehr gut das Konzept eines skalierbaren Codecs, da je nach gewünschter Skalierung nur einer, mehrere oder alle Frequenzbereiche übertragen werden können. Der CELP-Coder COD1 liefert einen Grundbeitrag S_G zum codierten Gesamtsignal S_GES. Der Transformcoder COD2 liefert einen Zusatzbeitrag S_Z zum codierten Gesamtsignal S_GES. Das codierte Gesamtsignal S_GES wird mittels einer Kommunikationsvorrichtung KC auf der Codiererseite C an eine Kommunikationsvorrichtung KD auf einer Decodiererseite D übertragen. Hier erfolgt ggf. eine Verarbeitung (beispielsweise eine Aufspaltung des codierten Gesamtsignals in die Beiträge S_G und S_Z) der Daten bzw. des empfangenen codierten Gesamtsignals S_GES in einer Verarbeitungseinrichtung PROC, wobei anschließend die verarbeiteten Daten bzw. das verarbeitete Signal einer Decodiereinrichtung DEC zur nachfolgenden Decodierung DEC übertragen werden (vgl. dazu auch die Figuren 3 und 4). An die Decodierung schließt sich eine Geräuschreduktion in einer Geräuschreduktionseinrichtung NR an, die in Figur 3 in größerem Detail dargestellt ist.In FIG. 1 the schematic flow of a coding and decoding process is shown by means of an embodiment. On an encoder side C, an analogue signal S to be transmitted to a receiver is preprocessed or preprocessed for the coding by means of a preprocessing device PP, for example by being digitized. Furthermore, a decomposition of the signal into time segments or frames in a subdivision unit F takes place. A signal prepared in this way is supplied to a coding unit COD. The coding unit COD comprises a hybrid coder comprising a first coder, a CELP coder COD1 and a second coder, a transform coder COD2. The CELP coder COD1 comprises a plurality of CELP coders COD1_A, COD1_B, COD1_C, which operate in different frequency ranges. Through this division into different frequency ranges a particularly accurate coding can be guaranteed. Furthermore, this division into different frequency ranges very well supports the concept of a scalable codec, since depending on the desired scaling only one, several or all frequency ranges can be transmitted. The CELP coder COD1 delivers a basic contribution S_G to the coded total signal S_GES. The transform coder COD2 provides an additional contribution S_Z to the coded total signal S_GES. The coded total signal S_GES is transmitted by means of a communication device KC on the coder side C to a communication device KD on a decoder side D. Here, if necessary, a processing (for example, a splitting of the coded total signal into the contributions S_G and S_Z) of the data or of the received coded total signal S_GES in a processing device PROC takes place, wherein subsequently the processed data or the processed signal of a decoding device DEC for subsequent decoding DEC transferred (see also the Figures 3 and 4 ). The decoding is followed by a noise reduction in a noise reduction device NR, which in FIG. 3 is shown in greater detail.

In FIG 2 ist ein erstes Kommunikationsgerät COM1 (beispielsweise repräsentierend die Komponenten auf der Codiererseite C von Figur 1) dargestellt, welches eine Sende- und Empfangseinheit ANT1 (beispielsweise entsprechend der Kommunikationsvorrichtung KC) zum Übertragen oder/und Empfangen von Daten, sowie eine Recheneinheit CPU1 aufweist, die zur Realisierung der Komponenten auf der Codiererseite C bzw. zur Durchführung des in FIG 1 dargestellten Codierverfahrens (Verarbeitung auf der Codiererseite C) eingerichtet ist. Die Übertragung von Daten erfolgt mittels der Sende/Empfangseinheit ANT1 über ein Kommunikationsnetz CN (das beispielsweise je nach zu verwendenden Kommunikationsgeräten als Internet, ein Telefonnetz bzw. Mobilfunknetz eingerichtet sein kann). Der Empfang erfolgt durch ein zweites Kommunikationsgerät COM2 (beispielsweise repräsentierend die Komponenten auf der rechten Seite der Figur 1), welches wiederum eine Sende- und Empfangseinheit ANT2 (beispielsweise entsprechend der Kommunikationsvorrichtung KB), sowie eine Recheneinheit CPU2 aufweist, welche zur Realisierung der Komponenten auf der Decodiererseite D bzw. zur Durchführung eines Decodierverfahrens (Verarbeitung auf der Decodiererseite D) gemäß FIG 1 eingerichtet ist. Beispiele für mögliche Realisierungen der Kommunikationsgeräte COM1 und COM2, in denen dieses Verfahren zur Anwendung kommen kann, sind IP-Telefone, Voice-Gateways oder Mobiltelefone.In FIG. 2 is a first communication device COM1 (for example, representing the components on the encoder side C of FIG FIG. 1 ), which has a transmitting and receiving unit ANT1 (for example, corresponding to the communication device KC) for transmitting and / or receiving data, as well as a computing unit CPU1, which for the realization of the components on the encoder side C or for performing the in FIG. 1 illustrated encoding method (processing on the encoder side C) is set up. The transmission of data by means of the transmitting / receiving unit ANT1 via a communication network CN (which, for example, depending on the communication devices to be used as the Internet, a telephone network or mobile network can be set up). The reception is performed by a second communication device COM2 (for example, representing the components on the right side of FIG FIG. 1 ), which in turn has a transmitting and receiving unit ANT2 (for example, corresponding to the communication device KB), and a computing unit CPU2, which for the realization of the components on the decoder side D or for performing a decoding method (processing on the decoder side D) FIG. 1 is set up. Examples of possible implementations of the communication devices COM1 and COM2 in which this method can be used are IP telephones, voice gateways or mobile telephones.

Es sei nun auf Figur 3 verwiesen, in der die Decodierungseinrichtung DEC und die Geräuschreduktionseinrichtung NR mit den wesentlichen Komponenten zur schematischen Darstellung des Ablaufs einer Pre-Echo-Reduktion zu sehen ist.
Ein CELP-codiertes Signal S_COD,CELP (entsprechend dem Signal S_G) wird mittels eines Gesamtband-CELP-Decodierers DEC_GES,CELP decodiert. Das decodierte Signal S_CELP wird einerseits zu einer (ersten) Energiehüllkurvenbestimmungseinheit GE1 zur Bestimmung der zugehörigen Hüllkurve ENV_CELP, anderseits zu einem TDAC(Time domain aliasing cancellation)Encoder COD_TDAC weitergeleitet. Bei der TDAC-Codierung handelt es sich um ein Beispiel für eine Transformcodierung.It is now up FIG. 3 in which the decoding device DEC and the noise reduction device NR with the essential components for the schematic representation of the sequence of a pre-echo reduction can be seen.
A CELP coded signal S_COD, CELP (corresponding to the signal S_G) is decoded by means of a full-band CELP decoder DEC_GES, CELP. The decoded signal S_CELP is forwarded, on the one hand, to a (first) energy envelope determination unit GE1 for determining the associated envelope ENV_CELP, and, on the other hand, to a time domain aliasing cancellation (TDAC) encoder COD_TDAC. TDAC encoding is an example of transform coding.

Das codierte Signal S_COD,CELP,TDAC wird zusammen mit dem von Empfängerseite stammenden transformcodierten Signal S_COD,TDAC (entsprechend dem Signal S_Z) zu einem Transformdecodierer DEC_TDAC geleitet, um ein decodiertes Signal S_TDAC zu erzeugen. Auch aus diesem decodierten Signal S_TDAC wird ebenfalls in einer (zweiten) Energiehüllkurvenbestimmungseinheit GE2 die zugehörige Energiehüllkurve ENV_TDAC bestimmt. In einer Verhältnisbestimmungseinheit D wird das Verhältnis R der Energiehüllkurven zueinander als Kennzahl zeitabschnittweise bestimmt. In einer Bedingungsfeststellungseinheit BFE wird festgestellt, ob das Verhältnis R einen festgelegten Mindestabstand von 1 (1: beide Energiehüllkurven gleich) hat, d.h. dass die Pegel beider Signale gleich sind oder zumindest nur um einen vorgegebenen Prozentsatz voneinander abweichen.The coded signal S_COD, CELP, TDAC, together with the receiver-side derived transform coded signal S_COD, TDAC (corresponding to the signal S_Z) are routed to a transform decoder DEC_TDAC to produce a decoded signal S_TDAC. The associated energy envelope ENV_TDAC is likewise determined from this decoded signal S_TDAC in a (second) energy envelope determination unit GE2. In a ratio determination unit D, the ratio R of the energy envelopes to each other as a measure is determined in portions. In a condition determination unit BFE, it is determined whether the ratio R has a fixed minimum distance of 1 (1: both energy envelopes equal), ie that the levels of both signals are the same or at least differ only by a predetermined percentage.

Ergebnis ist dann ein Verstärkungsfaktor bzw. Dämpfungsfaktor G, der im gezeigten Fall gleich dem Verhältnis R (Kennzahl) ist, mit dem der transformdecodierte Signalbeitrag S_TDAC in einer Multiplikationseinrichtung M multipliziert wird, um ein endgültiges störgeräuschreduziertes Signal S_OUT zu erhalten. Genauer gesagt, wird beispielsweise davon ausgegangen, dass das Verhältnis R gebildet wird durch R = ENV_CELP / ENV_TDAC, und wurde festgelegt, dass dieses Verhältnis einen vorbestimmten Schwellenwert SW nicht unterschreiten darf, so wird bei unterschreiten des Schwellenwerts SW der transformdecodierte Signalbeitrag S_TDAC mit einem Verstärkungsfaktor G, beispielsweise G = R multipliziert, was zu einer Dämpfung des Signalbeitrags S_TDAC führt. Es ist ferner möglich, in dem Fall, in dem der Schwellenwert SW nicht unterschritten wird, dem Verstärkungsfaktor G den Wert "1" zuzuordnen, so dass bei einer Multiplikation des Signalbeitrags S_TDAC, die dann in jedem Fall stattfinden kann, der Wert S_TDAC unverändert bleibt.The result is then an amplification factor or damping factor G, which in the case shown is equal to the ratio R (characteristic number) with which the transform-decoded signal contribution S_TDAC is multiplied in a multiplier M in order to obtain a final noise-reduced signal S_OUT. More specifically, for example, assuming that the ratio R is formed by R = ENV_CELP / ENV_TDAC, and it has been determined that this ratio should not fall short of a predetermined threshold value SW, when the threshold value SW is undershot, the transform decoded signal contribution S_TDAC becomes a gain factor G, for example G = R multiplied, which leads to an attenuation of the signal contribution S_TDAC. It is also possible, in the case in which the threshold value SW is not undershot, to assign the value "1" to the amplification factor G, so that when the signal contribution S_TDAC is multiplied, which then can take place in any case, the value S_TDAC remains unchanged ,

Somit kann im Fall einer Abweichung der Energie des transformdecodierten Signalbeitrags S_TDAC, wobei die Abweichung eben der genannte Pre-Echo-Effekt ist, die Energie bzw. der Pegel dieses Signalbeitrags zum zuverlässigeren Wert des CELP-decodierten Signals S_CELP bewegt werden, so dass das endgültige Signal S_out störgeräuschreduziert ist.Thus, in the case of a deviation of the energy of the transform decoded signal contribution S_TDAC, the deviation being the aforementioned pre-echo effect, the energy or the level of this signal contribution can be moved to the more reliable value of the CELP decoded signal S_CELP, so that the final Signal S_out noise is reduced.

Es sei nun auf Figur 4 verwiesen, anhand der eine weitere Ausführungsform zur Reduzierung des Pre-Echoeffekts erläutert werden soll.It is now up FIG. 4 Reference is made to explain a further embodiment for reducing the pre-echo effect.

Es ist möglich, dass anstelle nur eines CELP-codecs mehrere, nach Frequenzbereichen getrennte (CELP- oder andere) Codecs vorhanden sind. Die in Figur 4 gezeigte Ausführungsform entspricht größtenteils der in Figur 3 gezeigten Ausführungsform und stellt ein Erweiterung diesbezüglich dar, dass das in Figur 3 gezeigte Verfahren nicht auf die Gesamtsignale von CELP (oder anderen)-Decoder und Transformdecoder angewendet wird, sondern dass das Verfahren getrennt nach Frequenzbereichen angewendet wird. Das heißt, es findet zunächst eine Aufteilung des Gesamtsignals bzw. der einzelnen Signalbeiträge nach Frequenzbereichen statt, wobei das Verfahren von Figur 3 dann pro Frequenzbereich auf die einzelnen Signalbeiträge angewendet werden kann.It is possible that instead of just one CELP codec there are multiple (CELP or other) codecs separated by frequency ranges. In the FIG. 4 For the most part, the embodiment shown corresponds to that in FIG FIG. 3 shown embodiment and is an extension in this regard that the in FIG. 3 is not applied to the overall signals from CELP (or other) decoder and transform decoder, but that the method is applied separately to frequency ranges. That is, there is first a division of the total signal or the individual signal contributions to frequency ranges instead, the method of FIG. 3 then per frequency range can be applied to the individual signal contributions.

Der Vorteil davon wird im Folgenden erläutert. Beim Decoder ist für mehrere Frequenzbänder die Sollenergie für diese Frequenzbänder bekannt, nämlich aus der Energie der einzelnen nach Frequenzbereichen getrennten CELP-Signale. Der Transformdecoder liefert nun ein Add-on Signal (Zusatzbeitrag), welches jedoch in seiner Energie erheblich abweichen kann. Problematisch ist vor allem, wenn die Energie des Signals aus dem Transformdecoder erheblich zu hoch ist, z.B. aufgrund von Pre-Echo-Effekten. Das Verfahren führt nun für jedes einzeln behandelte Frequenzband eine Begrenzung der Transformcodec-Energie abhängig von der CELP-Energie ein. Dieses Verfahren ist umso effektiver, je mehr Frequenzbänder auf diese Weise getrennt behandelt werden.The advantage of this will be explained below. In the case of the decoder, the desired energy for these frequency bands is known for a plurality of frequency bands, namely from the energy of the individual CELP signals separated according to frequency ranges. The Transform Decoder now provides an add-on signal (additional contribution), which, however, can differ considerably in its energy. Particularly problematic is when the energy of the signal from the transform decoder is significantly too high, e.g. due to pre-echo effects. The method now introduces a limit on the Transformcodec energy depending on the CELP energy for each individually treated frequency band. This method is the more effective, the more frequency bands are treated separately in this way.

Dies wird anhand von folgendem Beispiel sofort deutlich:This is immediately apparent from the following example:

Das Gesamtsignal bestehe aus einem 2000 Hz Ton, welches gänzlich aus dem CELP codec Anteil kommt. Zusätzlich, aufgrund von Preecho Effekten liefert der Transformcodec nun noch ein Störsignal mit einer Frequenz von 6000 Hz; die Energie des Störsignals sei 10% der Energie des 2000 Hz Tons.
Das Kriterium zur Begrenzung des Transformcodec-Anteils sei, dass dieser max. gleich groß wie der CELP-Anteil sein darf. Fall 1: Es wird kein Splitting nach Frequenzbändern gemacht (erste Ausführungsform): Dann wird das 6000 Hz Störsignal nicht unterdrückt, da es nur 10% der Energie des 2000Hz Tons aus dem CELP Codec hat.The total signal consists of a 2000 Hz sound, which comes entirely from the CELP codec portion. In addition, due to Preecho effects, the Transformcodec now provides an interference signal with a frequency of 6000 Hz; the energy of the interfering signal is 10% of the energy of the 2000 Hz tone.
The criterion for limiting the Transformcodec share is that this max. the same size as the CELP share may be. Case 1: No splitting is made after frequency bands (first embodiment): Then the 6000 Hz interference signal is not suppressed since it has only 10% of the energy of the 2000 Hz tone from the CELP codec.

Fall 2: Die Frequenzbänder A: 0 - 4000 Hz und B: 4000 Hz - 8000 Hz werden getrennt behandelt (weitere Ausführungsform): In diesem Fall wird das Störsignal komplett unterdrückt, da im oberen Frequenzband der CELP-Anteil Null ist, und somit auch das Transformcodecsignal auf den Wert Null begrenzt wird.Case 2: The frequency bands A: 0 - 4000 Hz and B: 4000 Hz - 8000 Hz are treated separately (further embodiment): In this case, the interference signal is completely suppressed because in the upper frequency band, the CELP component is zero, and thus also the Transformcodecsignal is limited to the value zero.

In Figur 4 ist nun (entsprechend zu Figur 3) wieder eine Decodierungseinrichtung DEC und eine Geräuschreduktionseinrichtung NR mit den wesentlichen Komponenten zur schematischen Darstellung des Ablaufs einer Pegelanpassung bzw. Pre-Echo-Reduktion zu sehen. Für die Erzeugung von codierten Signalen bzw. die Übertragung an einen Empfänger sei wieder auf die Figuren 1 oder 2 verwiesen.In FIG. 4 is now (corresponding to FIG. 3 ) again to see a decoding device DEC and a noise reduction device NR with the essential components for the schematic representation of the sequence of a level adjustment or pre-echo reduction. For the generation of coded signals or the transmission to a receiver is again on the Figures 1 or 2 directed.

Ein CELP-codiertes Signal S_COD,CELP (entsprechend dem Signalbeitrag S_G) wird mittels eines Gesamtband-CELP-Decodierers DEC_GES,CELP' decodiert. Der Gesamtband-CELP-Decodierer umfasst dabei zwei Decodiereinrichtungen, eine erste Decodiereinrichtung DEC_FB_A zum Decodieren des Signals S_COD,CELP in einem ersten Frequenzband A und eine zweite Decodiereinrichtung DEC_FB_B zum Decodieren des Signals S_COD,CELP in einem zweiten Frequenzband B. Ein erstes decodiertes Signal S_CELP_A wird zu einer (ersten) Energiehüllkurvenbestimmungseinheit GE1_A zur Bestimmung der zugehörigen Hüllkurve ENV_CELP_A geleitet, während ein zweites decodiertes Signal S_CELP_B zu einer (zweiten) Energiehüllkurvenbestimmungseinheit GE1_B zur Bestimmung der zugehörigen Hüllkurve ENV_CELP_B geleitet wird.A CELP coded signal S_COD, CELP (corresponding to the signal contribution S_G) is decoded by means of a whole-band CELP decoder DEC_GES, CELP '. The total band CELP decoder comprises two decoding devices, a first decoder DEC_FB_A for decoding the signal S_COD, CELP in a first frequency band A and a second decoding device DEC_FB_B for decoding the signal S_COD, CELP in a second frequency band B. A first decoded signal S_CELP_A is passed to a (first) energy envelope determination unit GE1_A for determining the associated envelope ENV_CELP_A, while a second decoded signal S_CELP_B is sent to a (second) energy envelope determination unit GE1_B for determining the associated envelope ENV_CELP_B becomes.

Ein von der Empfängerseite stammendes transformcodiertes Signal S_COD,TDAC (entsprechend dem Signal S_Z) wird zu einem Transformdecodierer DEC_TDAC geleitet, um ein decodiertes Signal S_TDAC zu erzeugen, das wiederum einem Frequenzbandsplitter (Frequenzbandaufteiler) FBS zugeführt wird. Dieser teilt das Signal S_TDAC in zwei Signale, nämlich S_TDAC_A für das Frequenzband A und S_TDAC_B für das Frequenzband B auf. Die Aufteilung in Frequenzbänder kann optional auch im Frequenzbereich, vor der Rücktransformation in den Zeitbereich, erfolgen. Dadurch entfällt insbesondere die mit einem im Zeitbereich arbeitenden Frequenzbandsplitter (Hoch-,Tief-, oder Bandpassfilter) einhergehende Verzögerung. Auch aus diesen decodierten frequenzbandabhängigen Signalen S_TDAC_A und S_TDAC_B wird ebenfalls in einer (dritten) Energiehüllkurvenbestimmungseinheit GE2_A bzw. einer (vierten) Energiehüllkurvenbestimmungseinheit GE2_B die zugehörige Energiehüllkurve ENV_TDAC_A bzw. ENV_TDAC_B bestimmt.A receiver-side derived transform coded signal S_COD, TDAC (corresponding to the signal S_Z) is passed to a transform decoder DEC_TDAC to produce a decoded signal S_TDAC, which in turn is applied to a frequency band splitter (frequency band splitter) FBS. This divides the signal S_TDAC into two signals, namely S_TDAC_A for the frequency band A and S_TDAC_B for the frequency band B. The division into frequency bands can optionally also take place in the frequency domain, before the inverse transformation into the time domain. This eliminates in particular the delay associated with a frequency band splitter operating in the time domain (high, low, or bandpass filter). Also from these decoded frequency-band-dependent signals S_TDAC_A and S_TDAC_B, the associated energy envelope ENV_TDAC_A or ENV_TDAC_B is also determined in a (third) energy envelope determination unit GE2_A or a (fourth) energy envelope determination unit GE2_B.

In einer ersten Verstärkungsbestimmungseinheit BD_A wird für das Frequenzband A anhand der Energiehüllkurven ENV_CELP_A und ENV_TDAC_A ein Verstärkungsfaktor (oder auch Dämpfungsfaktor, da die Verstärkung negativ ist) G_A bestimmt, während in einer zweiten Verstärkungsbestimmungseinheit BD_B für das Frequenzband B anhand der Energiehüllkurven ENV_CELP_B und ENV_TDAC_B ein Verstärkungsfaktor (Dämpfungsfaktor) G_B bestimmt wird. Die Bestimmung der jeweiligen Verstärkungsfaktoren kann entsprechend der Bestimmung von Figur 3 (vgl. Komponenten D, BFE) von statten gehen. Es kann dabei beispielsweise wieder ein jeweiliges Verhältnis (Kennzahl) R_A, R_B der Energiehüllkurven für ein jeweiliges Frequenzband A und B, nämlich R_A = ENV_CELP_A/ ENV_TDAC_A bzw. R_B = ENV_CELP_B/ENV_TDAC_B gebildet werden, wobei für ein jeweiliges Frequenzband ein Schwellenwert SW_A bzw. SW_B festgelegt wird, bei dessen Unterschreiten ein jeweiliger Verstärkungsfaktor G_A (beispielsweise G_A = R_A) bzw. G_B (beispielsweise G_B = R_B) erzeugt wird, der schließlich auf ein jeweiliges frequenzbandabhängiges Signal S_TDAC_A bzw. S_TDAC_B anzuwenden ist (um eine Dämpfung herbeizuführen). Wird ein jeweiliger Schwellenwert nicht unterschritten kann ein jeweiliger Verstärkungsfaktor G_A bzw. G_B auf "1" festgelegt werden, so dass bei einer Multiplikation ein jeweiliges frequenzbandabhängiges Signal S_TDAC_A bzw. S_TDAC_B unverändert bleibt.In a first gain determination unit BD_A, a gain factor (or attenuation factor, since the gain is negative) G_A is determined for the frequency band A, while in a second gain determination unit BD_B for the frequency band B, a gain factor is calculated using the energy envelopes ENV_CELP_B and ENV_TDAC_B (Damping factor) G_B is determined. The determination of the respective amplification factors can according to the provision of FIG. 3 (see components D, BFE). In this case, for example, a respective ratio (characteristic number) R_A, R_B of the energy envelopes for a respective frequency band A and B, namely R_A = ENV_CELP_A / ENV_TDAC_A or R_B = ENV_CELP_B / ENV_TDAC_B, can again be formed, wherein for a respective frequency band a threshold value SW_A or SW_B, below which a respective amplification factor G_A (for example G_A = R_A) or G_B (for example G_B = R_B) is generated, which is finally to be applied to a respective frequency band-dependent signal S_TDAC_A or S_TDAC_B (to bring about a damping). If a respective threshold value is not undershot, a respective amplification factor G_A or G_B can be set to "1", so that when a multiplication occurs, a respective frequency band-dependent signal S_TDAC_A or S_TDAC_B remains unchanged.

In einer ersten Multiplikationseinrichtung M_A für das Frequenzband A wird schließlich der Verstärkungsfaktor G_A mit dem Signal S_TDAC_A und wird der Verstärkungsfaktor G_B mit dem Signal S_TDAC_B multipliziert. Schließlich werden die multiplizierten (eventuell gedämpften) frequenzbandabhängigen Signale zusammengeführt, um ein endgültiges störgeräuschreduziertes (Gesamtfrequenz-)Signal S_OUT' zu erzielen.In a first multiplication device M_A for the frequency band A, finally, the amplification factor G_A is multiplied by the signal S_TDAC_A and the amplification factor G_B is multiplied by the signal S_TDAC_B. Finally, the multiplied (possibly attenuated) frequency band dependent signals are combined to produce a final noise reduced (total frequency) signal S_OUT '.

Es sei bemerkt, dass obwohl im vorliegenden Beispiel lediglich eine Aufspaltung der decodierten Signalbeiträge S_CELP_A, S_CELP_B, S_TDAC_A und S_TDAC_B in zwei Frequenzbereiche A und B stattgefunden hat, eine Aufteilung auch in 3 oder mehr Frequenzbereiche möglich und vorteilhaft sein kann.It should be noted that although in the present example only a splitting of the decoded signal contributions S_CELP_A, S_CELP_B, S_TDAC_A and S_TDAC_B into two frequency ranges A and B has taken place, a division into 3 or more frequency ranges may be possible and advantageous.

Claims (15)

Verfahren zur Geräuschunterdrückung (S_OUT) bei einem decodierten Signal, welches sich aus einem ersten decodierten Signalbeitrag (S_CELP) und einem zweiten decodierten Signalbeitrag (S_TDAC) zusammensetzt mit folgenden Schritten: a. Ermitteln einer ersten Energiehüllkurve (ENV_CELP) und einer zweiten Energiehüllkurve (ENV_TDAC) des ersten Signalbeitrags (S_CELP) und des zweiten decodierten Signalbeitrags (S_TDAC); b. Bilden einer Kennzahl (R) in Abhängigkeit von einem Vergleich von erster und zweiter Energiehüllkurve (ENV_CELP, ENV_TDAC) ; c. Ableiten eines Verstärkungsfaktors (G) in Abhängigkeit von der Kennzahl (R). Method for noise suppression (S_OUT) in the case of a decoded signal which comprises a first decoded signal contribution (S_CELP) and a second decoded signal contribution (S_TDAC), comprising the following steps: a. Determining a first energy envelope (ENV_CELP) and a second energy envelope (ENV_TDAC) of the first signal contribution (S_CELP) and the second decoded signal contribution (S_TDAC); b. Forming a measure (R) in response to a comparison of the first and second energy envelopes (ENV_CELP, ENV_TDAC); c. Deriving an amplification factor (G) as a function of the index (R). Verfahren nach Anspruch 1 mit folgendem weiteren Schritt: d. Multiplizieren des zweiten decodierten Signalbeitrags (S_TDAC) mit dem Verstärkungsfaktor (G), wenn die Kennzahl (R) ein festgelegtes Kriterium (C) nicht erfüllt. Method according to Claim 1, with the following further step: d. Multiplying the second decoded signal contribution (S_TDAC) by the gain factor (G) if the index (R) does not satisfy a specified criterion (C). Verfahren nach einem der vorhergehenden Ansprüche, bei dem die decodierte Signalbeiträge (S_TDAC, S_CELP) in Zeitabschnitte unterteilt ist und die Schritte a) bis d) zeitabschnittweise erfolgen.Method according to one of the preceding claims, in which the decoded signal contributions (S_TDAC, S_CELP) are subdivided into time segments, and the steps a) to d) are performed on a time-wise basis. Verfahren nach Anspruch 3, bei dem die Länge der Zeitabschnitte für den ersten und den zweiten decodierten Signalbeitrag (S_TDAC, S_CELP) unterschiedlich ist und die Schritte a) bis d) zeitabschnittweise für den kürzeren Zeitabschnitt erfolgen.Method according to Claim 3, in which the length of the time segments for the first and second decoded signal contributions (S_TDAC, S_CELP) is different and steps a) to d) are carried out in sections for the shorter time segment. Verfahren nach einem der vorhergehenden Ansprüche, bei dem der erste decodierte Signalbeitrag (S_CELP) durch Decodieren eines ersten Codierbeitrags (S_COD,CELP)aus einem ersten Decodierer (DEC_GES,CELP) stammt und der zweite decodierte Signalbeitrag (S_TDAC) durch Decodieren eines zweiten Codierbeitrags (S_COD,TDAC, S_COD,CELP,TDAC) aus einem zweiten Decodierer (DEC_TDAC) stammt .Method according to one of the preceding claims, in which the first decoded signal contribution (S_CELP) is obtained by decoding a first coding contribution (S_COD, CELP) from a first decoder (DEC_GES, CELP) and the second decoded signal contribution (S_TDAC) by decoding a second encoding contribution ( S_COD, TDAC, S_COD, CELP, TDAC) originates from a second decoder (DEC_TDAC). Verfahren nach Anspruch 5, bei dem der zweite Codierbeitrag (S_TDAC) den ersten Codierbeitrag (S_CELP) enthält.Method according to Claim 5, in which the second coding contribution (S_TDAC) contains the first coding contribution (S_CELP). Verfahren nach einem der vorhergehenden Ansprüche, bei dem die Kennzahl (R) durch das Bilden des Verhältnisses von erster und zweiter Energiehüllkurve (ENV_CELP, ENV_TDAC) gebildet wird.Method according to one of the preceding claims, in which the characteristic number (R) is formed by forming the ratio of first and second energy envelope (ENV_CELP, ENV_TDAC). Verfahren nach einem der vorhergehenden Ansprüche, bei dem der Verstärkungsfaktor (G) gleich der Kennzahl (R) ist.Method according to one of the preceding claims, in which the amplification factor (G) is equal to the characteristic number (R). Verfahren nach einem der vorhergehenden Ansprüche, bei dem das erste decodierte Signal (S_CELP) durch Decodieren eines Signals (S_COD,CELP) gebildet wird, welches von einer Mehrzahl von ersten Codierern (COD1_A, COD1_B, COD_C) stammt, welche in unterschiedlichen Frequenzbereichen arbeiten.Method according to one of the preceding claims, in which the first decoded signal (S_CELP) is formed by decoding a signal (S_COD, CELP) originating from a plurality of first encoders (COD1_A, COD1_B, COD_C) operating in different frequency ranges. Verfahren nach einem der vorhergehenden Ansprüche 5 oder 6, bei dem der erste Decodierer (DEC_GES_CELP) durch einen CELP-Decodierer gebildet wird.Method according to one of the preceding claims 5 or 6, wherein the first decoder (DEC_GES_CELP) is formed by a CELP decoder. Verfahren nach einem der vorhergehenden Ansprüche 5, 6 oder 10, bei dem der zweite Decodierer (DEC_TDAC) durch einen Transform Decodierer gebildet wird.Method according to one of the preceding claims 5, 6 or 10, wherein the second decoder (DEC_TDAC) is formed by a transform decoder. Verfahren nach einem der vorhergehenden Ansprüche 5, 6, 10 oder 11, bei dem erster und zweiter Decodierer (DEC_TDAC, DEC_CELP) den gleichen Frequenzbereich umfassen.Method according to one of the preceding claims 5, 6, 10 or 11, in which the first and second decoders (DEC_TDAC, DEC_CELP) comprise the same frequency range. Verfahren zur Geräuschunterdrückung bei einem einem Frequenzband zugeordneten decodierten Signal , welches sich aus einem jeweiligen ersten decodierten Signalbeitrag (S_CELP_A, S_CELP_B) und einem jeweiligen zweiten decodierten Signalbeitrag (S_TDAC_A, S_TDAC_B) für ein jeweiliges Teilfrequenzband des Frequenzbands zusammensetzt, mit folgenden Schritten: a. Ermitteln einer ersten Energiehüllkurve (ENV_CELP_A, ENV_CELP_B) des jeweiligen ersten decodierten Signalbeitrags und einer zweiten Energiehüllkurve (ENV_TDAC_A, ENV_TDAC_B) und des jeweiligen zweiten decodierten Signalbeitrags für ein jeweiliges Teilfrequenzband; b. Bilden einer jeweiligen Kennzahl (R_A, R_B) in Abhängigkeit von einem Vergleich von erster und zweiter Energiehüllkurve für ein jeweiliges Teilfrequenzband; c. Ableiten eines jeweiligen Verstärkungsfaktors (G_A, G_B) in Abhängigkeit von der jeweiligen Kennzahl für ein jeweiliges Teilfrequenzband. A method for noise suppression in a decoded signal associated with a frequency band, which is composed of a respective first decoded signal contribution (S_CELP_A, S_CELP_B) and a respective second decoded signal contribution (S_TDAC_A, S_TDAC_B) for a respective frequency band of the frequency band, comprising the following steps: a. Determining a first energy envelope (ENV_CELP_A, ENV_CELP_B) of the respective first decoded signal contribution and a second energy envelope (ENV_TDAC_A, ENV_TDAC_B) and the respective second decoded signal contribution for a respective sub-frequency band; b. Forming a respective characteristic number (R_A, R_B) as a function of a comparison of the first and second energy envelope for a respective sub-frequency band; c. Deriving a respective amplification factor (G_A, G_B) as a function of the respective characteristic number for a respective subfrequency band. Verfahren nach Anspruch 13 mit folgendem weiteren Schritt: d. Multiplizieren des zweiten decodierten Signalbeitrags (S_TDAC_A, S_TDAC_B) mit dem jeweiligen Verstärkungsfaktor (G_A, G_B) für ein jeweiliges Teilfrequenzband, wenn die jeweilige Kennzahl (R_A, R_B) ein festgelegtes Kriterium nicht erfüllt. Method according to claim 13, with the following further step: d. Multiplying the second decoded signal contribution (S_TDAC_A, S_TDAC_B) by the respective gain factor (G_A, G_B) for a respective subfrequency band when the respective key figure (R_A, R_B) does not fulfill a defined criterion. Vorrichtung, insbesondere Kommunikationsgerät, mit einer Recheneinheit (CPU2), die zur Durchführung eines Verfahrens nach Anspruch 1 bis 14 ausgebildet ist.Device, in particular communication device, with a computing unit (CPU2), which is designed to carry out a method according to claim 1 to 14.
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PL1869671T3 (en) 2009-12-31
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JP4819881B2 (en) 2011-11-24
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US20070282604A1 (en) 2007-12-06
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US8612236B2 (en) 2013-12-17
ATE435481T1 (en) 2009-07-15

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