WO2011007813A1 - ハウリングキャンセラ - Google Patents
ハウリングキャンセラ Download PDFInfo
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- WO2011007813A1 WO2011007813A1 PCT/JP2010/061923 JP2010061923W WO2011007813A1 WO 2011007813 A1 WO2011007813 A1 WO 2011007813A1 JP 2010061923 W JP2010061923 W JP 2010061923W WO 2011007813 A1 WO2011007813 A1 WO 2011007813A1
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- notch filter
- howling
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R3/00—Circuits for transducers, loudspeakers or microphones
- H04R3/02—Circuits for transducers, loudspeakers or microphones for preventing acoustic reaction, i.e. acoustic oscillatory feedback
Definitions
- the present invention relates to a howling canceller that suppresses howling that occurs in an acoustic feedback system from a speaker to a microphone.
- the notch filter since it is intended to reduce sharply the gain of certain bandwidth, there is a problem that the sound quality is deteriorated.
- the inserted notch filter is not opened until the number of notch filters is insufficient. Depending on the situation, howling may be suppressed.
- a notch filter having a frequency at which howling has been eliminated due to a change in the acoustic feedback system or the like remains inserted. There is a possibility.
- an object of the present invention is to provide a howling canceller that appropriately opens a notch filter in accordance with howling occurs.
- a howling canceller is a howling canceller applied to an acoustic system having a microphone and a speaker, wherein a notch filter is inserted into a frequency of a collected sound signal of the microphone, and the notch filter is inserted.
- the setting means is a howling canceller that sets the notch filter insertion time to be shorter as the frequency at which the notch filter is inserted is higher.
- the howling canceller further includes movement amount detection means for detecting the movement amount of the microphone, and the setting means increases the notch filter as the movement amount of the microphone detected by the movement amount detection means increases. Set to shorten the insertion time.
- the howling canceller further includes range setting means for setting a movable range of the microphone, and the setting means is configured to collect sound from the microphone based on the movable range of the microphone set by the range setting means.
- a threshold value for dividing the frequency of the signal into a low frequency and a high frequency is determined, and the insertion time of the notch filter is set to be different between the low frequency and the high frequency.
- the setting means sets the insertion time of the notch filter inserted in the high band to be shorter than the insertion time of the notch filter inserted in the low band.
- the filter insertion means inserts a low-frequency notch filter and a high-frequency notch filter into a low frequency region and a high frequency region of the collected sound signal of the microphone, respectively, and is inserted into the low frequency region.
- the upper limit number of low-frequency notch filters is set.
- the filter insertion means sets an upper limit number of a plurality of notch filters to be inserted into the frequency of the sound pickup signal of the microphone, and the setting means inserts the plurality of notches into the frequency of the sound pickup signal of the microphone.
- the number of notch filters reaches the upper limit number, a band including a plurality of frequencies suppressed by a plurality of notch filters inserted in a high band is suppressed by one notch filter.
- the howling canceller further includes a movement amount detection unit that detects a movement amount of the microphone, and the setting unit is configured to detect the movement amount of the microphone based on the movement amount of the microphone detected by the movement amount detection unit.
- a threshold for dividing the frequency of the collected sound signal into a low frequency and a high frequency is set, and the opening means opens the notch filter inserted in the high frequency when the threshold is set.
- the movement amount detection means includes an acceleration sensor provided in the microphone, and the movement amount of the microphone is detected by the acceleration sensor.
- the movement amount detection means measures the distance between the microphone and the speaker by the microphone detecting the sound emitted from the speaker, and based on the measured distance, the microphone The amount of movement is detected.
- the microphone further includes threshold setting means for setting a threshold for dividing the frequency of the sound pickup signal of the microphone into a low frequency and a high frequency, and the setting means opens a notch filter inserted in the low frequency.
- threshold setting means for setting a threshold for dividing the frequency of the sound pickup signal of the microphone into a low frequency and a high frequency
- the setting means opens a notch filter inserted in the low frequency.
- the howling canceller of the present invention can appropriately open the notch filter depending on the situation in which howling occurs.
- FIG. 1 It is a block diagram which shows the function and structure of an acoustic system. It is a figure which shows an example of a filter coefficient.
- A)-(D) is an example of a counter table used for calculating the insertion time of the notch filter.
- (A), (B) is explanatory drawing regarding the notch filter which concerns on Example 4.
- FIG. 1 It is a block diagram which shows the function and structure of an acoustic system. It is a figure which shows an example of a filter coefficient.
- (A)-(D) is an example of a counter table used for calculating the insertion time of the notch filter.
- (A), (B) is explanatory drawing regarding the notch filter which concerns on Example 4.
- FIG. 1 is a block diagram showing the function and configuration of an acoustic system.
- the acoustic system 100 includes a microphone M, the howling canceller 1A, amplifier 2, and the speaker S.
- the sound signal collected by the microphone M is amplified by the amplifier 2 and then emitted from the speaker S as sound.
- the sound emitted from the speaker S is picked up by the microphone M again.
- the sound emitted from the speaker S is fed back to the microphone M and amplified by the amplifier 2 to form a closed loop.
- the loop gain of this closed loop exceeds 1, howling occurs. Therefore, in this acoustic system 100, the howling that has occurred is eliminated by using the howling canceller 1A.
- the microphone M picks up surrounding sounds (including sounds emitted from the speaker S), generates a sound signal, and outputs the sound signal to the howling canceller 1A and the amplifier 2.
- the amplifier 2 amplifies the input audio signal and outputs it to the notch filter 13 of the howling canceller 1A.
- the howling canceller 1A suppresses the frequency component in which howling of the input audio signal occurs.
- the howling canceller 1 ⁇ / b> A includes a howling detection unit 11, a filter coefficient generation unit 12, and a plurality of notch filters 13. The number of notch filters 13 is limited based on the performance and settings of hardware (microcomputer or the like) constituting the filter. Further, the howling canceller 1 ⁇ / b> A outputs the audio signal input from the microphone M to the howling detection unit 11.
- Howling detection unit 11 subjects the input speech signal, it performs a fast Fourier transform process to convert the audio signal into a frequency spectrum.
- the howling detection unit 11 detects a frequency component having a power level equal to or higher than a predetermined value from the frequency spectrum (that is, a frequency component in which howling has occurred), and outputs the detected frequency component to the filter coefficient generation unit 12.
- the filter coefficient generator 12 controls insertion and release of the notch filter 13. Specifically, the filter coefficient generation unit 12 generates a filter coefficient that suppresses a predetermined frequency component (frequency component in which howling is generated) of the audio signal input from the amplifier 2. Further, the filter coefficient generation unit 12 opens the notch filter 13 when the insertion time of the notch filter 13 passes the insertion time (the time when the filter 13 should be opened) is reached. Details of the processing of the filter coefficient generation unit 12 will be described later.
- the notch filter 13 suppresses the frequency component in which howling of the audio signal input from the amplifier 2 is suppressed, and outputs it to the speaker S.
- the speaker S emits sound based on the sound signal input from the howling canceller 1A (that is, the sound signal after the frequency component in which howling is suppressed).
- FIG. 2 is a diagram illustrating an example of a list (filter table) of inserted notch filters.
- the filter coefficient generation unit 12 stores a filter table as shown in FIG. 2, and generates a plurality of notch filters (filter coefficients) corresponding to various parameters of the filter table.
- the center frequency, bandwidth, and gain amount to be attenuated are registered for each notch filter 13 (filter 13A, filter 13B, filter 13C,).
- the notch filter 13 attenuates the gain amount with respect to a signal having a bandwidth centered on the center frequency.
- the filter 13A attenuates the gain by 24 dB with respect to an audio signal in a band of 95 Hz to 105 Hz (a bandwidth of 10 Hz centered on 100 Hz).
- the filter 13C attenuates the gain by 24 dB with respect to the audio signal in the band of 1.15 kHz to 1.25 kHz (0.1 kHz bandwidth centering on 1.2 kHz). Note that the amount of gain to be attenuated is not limited to 24 dB.
- the bandwidth is not limited to 10 Hz and 0.1 kHz.
- the filter coefficient generation unit 12 controls insertion and release of the notch filter 13 by registering and deleting the center frequency, bandwidth, and gain amount in the filter table. Specifically, when the notch filter 13 is inserted, the filter coefficient generation unit 12 registers the center frequency, the bandwidth, and the gain amount for inserting the notch filter 13 in the filter table. When the notch filter 13 is opened, the filter coefficient generation unit 12 deletes the center frequency, bandwidth, and gain amount in which the notch filter 13 has been inserted from the filter table. And the filter coefficient production
- the filter coefficient generation unit 12 inserts the notch filter 13 so as to suppress the frequency component. That is, the filter coefficient generation unit 12 registers the bandwidth and the gain amount in the filter table with the frequency as the center frequency.
- the filter coefficient generation unit 12 stores the insertion time of each notch filter 13 and deletes the center frequency, bandwidth, and gain amount of the notch filter 13 that have reached the time to be released from the filter table.
- the frequency at which howling occurs depends on the installation environment (for example, the size and shape of the room where the acoustic system is installed), the usage status (for example, the distance between the microphone and the speaker, the air flow due to the movement of people), etc. It depends on.
- the closed loop is determined by the installation environment. In the closed loop, when the phases of the specific frequency components are aligned, the loop gain increases. When the loop gain exceeds 1, howling occurs.
- the wavelength is long, so that howling is not easily affected by changes in the path length of the closed loop, and is greatly affected by other installation environments such as wall reflection. Therefore, in the case of a low frequency, even if the microphone M moves, the occurrence of howling is not easily affected by the phase change in the closed loop, and the loop gain is not easily less than 1. Therefore, it takes a long time until the notch filter 13 is opened. Should be set.
- the filter coefficient generation unit 12 sets the insertion time of the notch filter 13 (the time from when the notch filter 13 is inserted until it is released) longer as the frequency is lower, and sets the insertion time of the notch filter 13 shorter as the frequency is higher. To do.
- the filter coefficient generation unit 12 provides a counter C for each notch filter 13.
- the counter C indicates the added value of the count value per unit time, and is expressed using the following formulas 1 and 2.
- the filter coefficient generation unit 12 determines that the time elapsed since the insertion of the corresponding notch filter 13 has reached the insertion time (the insertion time of the notch filter 13 has elapsed). Then, the notch filter 13 that has reached the insertion time is opened.
- the filter coefficient generation unit 12 sets the insertion time of the notch filter 13 in accordance with howling occurs. As a result, the filter coefficient generation unit 12 can appropriately open the notch filter 13 in accordance with howling occurs. Further, the filter coefficient generation unit 12 prevents deterioration of sound quality by releasing the suppression by the notch filter 13 in a short time to a frequency (high frequency) where the presence or absence of howling is easily changed under the influence of the usage situation. be able to.
- FIGS. 3A to 3D are examples of a counter table used for calculating the insertion time of the notch filter.
- Y represents a count value per unit time (Y (F) in Equation 2) to the counter C.
- F indicates a frequency
- T indicates a threshold value between a low frequency and a high frequency.
- FIG. 3A is an example in which the increase rate of the counter in the low range is high and the increase rate of the counter in the high range is low.
- FIG. 3B shows an example in which the increase rate of the counter in the low range is high (in particular, the counter increase rate is higher as the frequency is lower in the low range), and the increase rate of the counter in the high range is 0. . That is, in this example, the amount of increase in the counter in the low range increases, but the amount of increase in the counter in the high range is constant.
- FIG. 3C is an example in which the increase amount of the counter in the low range and the increase amount of the counter in the high range are constant, and the increase amount of the counter is different between the low range and the high range.
- FIG. 3D is an example in which the increment of the counter in the low band is 0 (the notch filter inserted in the low band is not opened), and the increase rate of the counter in the high band is high.
- the filter coefficient generation unit 12 can shorten the insertion time of the notch filter 13 as it goes higher.
- a predetermined value for example, 2 kHz, 3 kHz, or the like
- a notch in a band lower than a threshold for example, 2 kHz, approximately 17 cm when converted to a movable range
- the notch filter inserted in the band above the threshold is not opened, and the notch filter inserted in the frequency above the threshold is counted up with an addition value proportional to the frequency inserted, so the notch filter inserted in the frequency above the threshold has a high frequency
- the insertion time is set shorter.
- the threshold values for the high frequency range and the low frequency range may be calculated based on the movable range of the microphone as shown below. Based on the movable range of the microphone, a method of calculating the threshold value between the low range and the high range will be described.
- the frequency F (Hz) is expressed by the following Expression 3 and Expression 4, where the sound speed is V (m / s) and the wavelength is ⁇ (m).
- V 340 Formula 4
- howling is considered to be canceled because the phase is reversed when the microphone M moves by an amount corresponding to the half wavelength of the sound. That is, it is considered that the moving amount L of the microphone M is regarded as a half wavelength, and howling of the frequency is eliminated. Moreover, since the frequency whose wavelength is longer than the movement amount L of the microphone M does not reach the half wavelength, howling is hardly suppressed by the movement of the microphone.
- the threshold T is expressed by the following equation (5).
- the howling canceller 1A calculates a threshold value between the low range and the high range with the movable range of the microphone as a half wavelength, and thereby obtains an appropriate threshold value according to changes in the installation environment and usage conditions. Can do.
- a howling canceller 1B (not shown) according to Embodiment 2 of the present invention will be described.
- the howling canceller 1B is different from the howling canceller 1A according to the first embodiment in that the notch filter 13 includes a low band and a high band. Only the differences will be described below. Note that the howling canceller 1B is not shown in the figure because the notch filter 13 is different from the howling canceller 1A in that the notch filter 13 is provided for low frequency and high frequency.
- the number of notch filters 13 included in the howling canceller is limited based on the performance and settings of the hardware constituting the filter. Further, since the insertion time of the notch filter 13 is set to be longer for the low frequency range, the filter coefficient generation unit 12 is assigned to the low frequency region than the high frequency region if the notch filter 13 is shared between the low frequency region and the high frequency region. The number of 13 tends to increase.
- the upper limit number is set for each of the low frequency notch filter and the high frequency notch filter.
- the upper limit number is set separately such as 5 for low frequency and 5 for high frequency, or 6 for low frequency and 4 for high frequency.
- the filter coefficient generation unit 12 sets the upper limit number by dividing the notch filter 13 for low frequency and for high frequency, so that the number of notch filters assigned to the low frequency does not become extremely large.
- the notch filter 13 can be appropriately assigned to the low range and the high range.
- the howling canceller 1 ⁇ / b> C according to the third embodiment is different from the howling canceller 1 ⁇ / b> A according to the first embodiment in that the notch filter 13 is divided into a low band, a middle band, and a high band, and the insertion time is set.
- the howling canceller 1C has the same block diagram as the howling canceller 1A, and is not shown.
- the filter coefficient generation unit 12 is set so as not to be opened after the notch filter 13 is inserted in the low band.
- the filter coefficient generation unit 12 inserts a filter with a wide bandwidth (band suppression filter) that suppresses the frequency band around the frequency where the howling has occurred, and sets the insertion time short.
- the insertion time of the high frequency notch filter is shorter than the insertion time of the mid frequency notch filter.
- the bandwidth of the high-frequency notch filter is wider than that of the mid-frequency notch filter.
- the middle band the filter coefficient generating unit 12 inserts the notch filter 13 to a frequency at which the howling has occurred and sets the insertion time.
- the filter coefficient generation unit 12 sets a band around a threshold (a predetermined value or a value calculated based on a wavelength) between the low band and the high band as a middle band.
- the howling canceller 1C is a mode in which the upper limit number is set by dividing the notch filter 13 into a low-frequency notch filter, a high-frequency notch filter, and a mid-frequency notch filter, like the howling canceller 1B of the second embodiment. There may be.
- the notch filter 13 is appropriately opened according to the howling occurrence state by changing the suppression bandwidth and the insertion time in the low, high, and mid ranges. be able to.
- 4A and 4B are explanatory diagrams relating to the notch filter according to the fourth embodiment.
- a plurality of frequency bands whose gains are suppressed by a plurality of notch filters 13 are collectively suppressed by one filter (a plurality of notch filters 13 are merged).
- 4A shows the frequency characteristics before merging of the plurality of notch filters 13
- FIG. 4B shows the frequency characteristics after merging of the plurality of notch filters 13
- the broken line shows a plurality of notch filters. 13 shows frequency characteristics before merging.
- the howling canceller 1D according to the fourth embodiment is different from the howling canceller 1A according to the second embodiment in that a plurality of notch filters 13 are merged.
- the howling canceller 1D has the same block diagram as the howling canceller 1A, and is not shown.
- the filter coefficient generation unit 12 has a limited number of notch filters 13 that exist at the same time. Therefore, when new howling is detected after all the notch filters 13 are inserted, the notch filter for suppressing the newly detected howling. 13 will be insufficient. Therefore, a plurality of notch filters 13 set in a high frequency range that is easily affected by the movement of the microphone M are merged.
- the filter coefficient generation unit 12 includes a notch filter 13 having a frequency f1 as a center frequency and a notch filter 13 having a frequency f2 as a center frequency (see FIG. 4A). These two notch filters 13 are changed to one notch filter 13 having a wide bandwidth having a center frequency (f1 + f2) / 2 between the frequencies f1 and f2 (see FIG. 4B). As a result, the filter coefficient generation unit 12 can open one notch filter 13, and therefore, newly generated howling can be suppressed using the opened notch filter 13.
- the filter coefficient generation unit 12 selects and merges the notch filters 13 having the closest center frequencies.
- the filter coefficient generation unit 12 can suppress the frequency components in which howling is newly generated by merging the notch filters 13. Further, the filter coefficient generation unit 12 can shorten the suppression time of the frequency component in which no howling has occurred by merging a plurality of high-frequency notch filters 13 having a short insertion time. As a result, the howling canceller 1 ⁇ / b> A can reduce deterioration of the output voice. Furthermore, the filter coefficient generating unit 12, by frequency merge multiple notch filters 13 close, it is possible to reduce the suppressing frequency components. As a result, the howling canceller 1 ⁇ / b> A does not further deteriorate the sound to be output.
- the howling canceller 1E according to the fifth embodiment is different from the howling canceller 1A according to the first embodiment in that the notch filter 13 is opened according to the moving amount L of the microphone.
- the howling canceller 1E has the same block diagram as the howling canceller 1A, and is not shown.
- the movement amount L of the microphone is detected by an acceleration sensor (not shown) attached to the microphone M.
- the filter coefficient generation unit 12 selects the notch filter 13 to be opened based on the movement amount L of the microphone. For example, the frequency (threshold value) may be calculated with the movement amount L of the microphone as a half wavelength, and all the notch filters 13 inserted in a higher range than the frequency may be opened.
- the movement of the microphone M is not limited to the detection by the acceleration sensor, but may be detected by measuring the distance between the speaker S and the microphone M.
- a method for measuring the distance for example, a method in which a measurement sound is emitted from the speaker S and an arrival time until the measurement sound is received by the microphone M can be considered.
- the howling canceller 1D can appropriately open the notch filter 13 according to howling occurs only by detecting the movement amount L of the microphone.
- the moving amount L of the microphone is calculated based on the movable range of the speaker (movable range of the microphone).
- the method for detecting the moving amount L of the microphone described in the fifth embodiment is performed. It may be applied to Example 1 and the threshold value for dividing the low range and the high range may be calculated based on the detected movement amount L of the microphone.
- the howling canceller of the present invention is applied to an acoustic system having a microphone and a speaker.
- the howling canceller includes a plurality of notch filters, and the insertion time of the notch filter is set based on the frequency at which the notch filter is inserted.
- a notch filter inserted at a high frequency is set to have a shorter insertion time than a notch filter inserted at a low frequency. That is, the higher the frequency at which the notch filter is inserted, the shorter the insertion time.
- the frequency at which howling occurs depends on the installation environment (for example, the size and shape of the room where the acoustic system is installed), the usage status (for example, the distance between the microphone and the speaker, the air flow due to the movement of people), etc. It depends on. Further, as one of the factors that cause howling, there is a case where the loop gain increases due to phase alignment in a closed loop between the speaker and the microphone. When this loop gain increases and exceeds 1, howling occurs. That is, since the wavelength is long at low frequencies, the influence of the phase change due to the movement of the microphone is small, and is largely due to the influence of other installation environments such as reflection of the wall surface. On the other hand, at a high frequency, the wavelength is short, so the influence of phase change due to movement of the microphone is large.
- the howling canceller of the present invention it is considered that the higher the frequency, the more the howling is suppressed by the movement of the microphone, and the insertion time is shortened as the frequency where the notch filter is inserted is higher.
- the howling canceller according to the present invention appropriately opens the notch filter according to the situation in which howling occurs (whether it is easily affected by the installation environment or the usage situation such as movement of the microphone). can do. Therefore, deterioration in sound quality can be prevented by switching the suppression of the gain of a frequency (high frequency) at which howling is easily suppressed in a short time.
- the howling canceller of the present invention measures a movement amount input means for inputting a movement amount of the microphone (for example, a setting means for setting a movable range of the microphone, an acceleration sensor attached to the microphone, and a distance between the microphone and the speaker. Means).
- a movement amount input means for inputting a movement amount of the microphone for example, a setting means for setting a movable range of the microphone, an acceleration sensor attached to the microphone, and a distance between the microphone and the speaker. Means.
- the howling canceller shortens the insertion time as the movement amount of the microphone increases.
- the howling canceller can prevent the frequency gain at which the howling has been eliminated from being maintained by reducing the insertion time of the notch filter as the amount of movement of the microphone increases.
- the howling canceller of the present invention may include range setting means for setting the movable range of the microphone.
- the howling canceller determines the threshold that is the boundary between the low range and the high range by setting the movable range of the microphone according to the application of the acoustic system to be applied, and is divided by this threshold value. Change the insertion time between low and high frequencies.
- the howling canceller sets a movable range of the microphone in advance and regards this movable range as a half wavelength.
- a wavelength longer than this wavelength (low frequency) is attributed to the installation environment, and it is assumed that howling is hardly suppressed by movement of the microphone, and a short wavelength (high frequency) is assumed that howling is easily suppressed by movement of the microphone. Therefore, the howling canceller can appropriately suppress howling by changing the insertion time before and after the frequency corresponding to the movable range of the microphone as a threshold value.
- the howling canceller of the present invention may be configured such that a plurality of notch filters are divided into a low band and a high band and the upper limit number is set.
- the howling canceller divides the notch filter into a low band and a high band and sets an upper limit number, so that an excessive number of notch filters are not allocated to the low band and the low band and the high band are not allocated.
- a notch filter can be appropriately assigned to each region.
- the howling canceller according to the present invention may be configured to suppress the frequency suppressed by a plurality of notch filters inserted in a high band with one filter having a wide bandwidth when the number of notch filters is insufficient.
- the howling canceller has a short insertion time in the high frequency band and is less affected by sound quality degradation.
- the number of notch filters used can be reduced. can do.
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Abstract
Description
Y(F)=logkF(k=定数)・・・式2
フィルタ係数生成部12は、カウンタCの値が所定値を超えると、対応するノッチフィルタ13を挿入してから経過した時間が挿入時間に達した(ノッチフィルタ13の挿入時間が経過した)と判断して、挿入時間に達したノッチフィルタ13を開放する。
例えば、図3(D)に示すカウンタテーブルを採用したハウリングキャンセラの場合、ユーザが自動フィルタ開放機能をONにしたときに、閾値(例えば2kHz、可動範囲に換算すると約17cm)より低い帯域のノッチフィルタは開放せず、閾値以上の帯域に挿入されたノッチフィルタは、その挿入されている周波数に比例した加算値でカウントアップされるので、閾値以上の周波数に挿入されたノッチフィルタは周波数が高いほど挿入時間が短く設定される。
マイクの可動範囲に基づいて、低域と高域との閾値の算出方法について説明する。周波数F(Hz)は、音速をV(m/s)、波長をλ(m)とすると、次の式3,式4で表される。
V=340 ・・・式4
ここで、ハウリングは、音声の半波長に対応する量だけマイクMが移動すると、位相が反転するため解消すると考えられる。すなわち、マイクMの移動量Lを半波長とみなし、その周波数のハウリングは解消すると考えられる。また、マイクMの移動量Lより波長が長い周波数は、半波長に達しないため、マイクの移動によりハウリングは抑制されにくい。
一般に、マイクMは、話者により保持され、話者の移動に伴って移動するものである。そこで、マイクの移動量Lは、話者の可動範囲(マイクの可動範囲)に基づいて算出する。例えば、舞台上で演説するような場合には、話者は、舞台上を頻繁に移動するものではなく、身振り手振り話をすることが多い。このため、手を動かす距離(1m)を半波長とする。この場合、閾値Tは、170/1=170Hzとなる。また、例えば、話者が舞台上を動くような場合は、舞台上を移動する距離(5m)を半波長とする。この場合、閾値Tは、170/5=34Hzとなる。このように、マイクの移動量Lは、話者の可動範囲(マイクの可動範囲)、すなわち音響システムの用途に基づいて算出することができる。
なお、実施例1では、マイクの移動量Lは、話者の可動範囲(マイクの可動範囲)に基づいて算出しているが、実施例5に記載のマイクの移動量Lの検出手法を実施例1に適用し、検出したマイクの移動量Lに基づいて低域と高域とを分ける閾値を算出してもよい。
この発明のハウリングキャンセラは、マイクとスピーカとを有する音響システムに適用される。ハウリングキャンセラは、複数のノッチフィルタを備え、ノッチフィルタが挿入されている周波数に基づいて当該ノッチフィルタの挿入時間が設定される。ハウリングキャンセラは、高い周波数に挿入されるノッチフィルタは、低い周波数に挿入されるノッチフィルタよりも挿入時間が短く設定される。つまり、ノッチフィルタが挿入されている周波数が高域であるほど、挿入時間が短時間に設定される。
本出願は、2009年7月17日出願の日本特許出願(特願2009-168559)に基づくものであり、その内容はここに参照として取り込まれる。
Claims (10)
- マイクとスピーカとを有する音響システムに適用されるハウリングキャンセラであって、
前記マイクの収音信号の周波数にノッチフィルタを挿入するフィルタ挿入手段と、
前記ノッチフィルタが挿入されている周波数に基づいて、前記ノッチフィルタの挿入時間を設定する設定手段と、
前記設定手段が設定した挿入時間が経過すると、該挿入時間を経過したノッチフィルタを開放する開放手段と、
を備え、
前記設定手段は、前記ノッチフィルタが挿入されている周波数が高いほど、該ノッチフィルタの挿入時間を短くするように設定するハウリングキャンセラ。 - 前記マイクの移動量を検出する移動量検出手段を更に備え、
前記設定手段は、前記移動量検出手段で検出されたマイクの移動量が大きくなるほど、前記ノッチフィルタの挿入時間を短くするように設定する請求項1に記載のハウリングキャンセラ。 - 前記マイクの可動範囲を設定する範囲設定手段を更に備え、
前記設定手段は、前記範囲設定手段が設定した前記マイクの可動範囲に基づいて、前記マイクの収音信号の周波数を低域と高域とに分ける閾値を決定し、前記低域と高域とで前記ノッチフィルタの挿入時間が異なるように設定する請求項1に記載のハウリングキャンセラ。 - 前記設定手段は、前記低域に挿入されるノッチフィルタの挿入時間より前記高域に挿入されるノッチフィルタの挿入時間を短くするように設定する請求項3に記載のハウリングキャンセラ。
- 前記フィルタ挿入手段は、前記マイクの収音信号の周波数の低域及び高域にそれぞれ低域用のノッチフィルタと高域用のノッチフィルタとを挿入し、前記低域に挿入される前記低域用のノッチフィルタの上限数を設定する請求項1に記載のハウリングキャンセラ。
- 前記フィルタ挿入手段は、前記マイクの収音信号の周波数に挿入する複数のノッチフィルタの上限数を設定し、
前記設定手段は、前記マイクの収音信号の周波数に挿入する前記複数のノッチフィルタが前記上限数に達した場合、高域に挿入された複数のノッチフィルタが抑制する複数の周波数を含む帯域を、1つのノッチフィルタで抑制する請求項1に記載のハウリングキャンセラ。 - 前記マイクの移動量を検出する移動量検出手段を更に備え、
前記設定手段は、前記移動量検出手段で検出された前記マイクの移動量に基づいて、前記マイクの収音信号の周波数を低域と高域とに分ける閾値を設定し、
前記開放手段は、前記閾値が設定されたときに、前記高域に挿入されているノッチフィルタを開放する請求項1に記載のハウリングキャンセラ。 - 前記移動量検出手段は、前記マイクに設けられた加速度センサを有し、前記加速度センサによって前記マイクの移動量を検出する請求項7に記載のハウリングキャンセラ。
- 前記移動量検出手段は、前記スピーカから放音された音声を前記マイクが検出することによって前記マイクと前記スピーカとの距離を測定し、該測定された距離に基づいて前記マイクの移動量を検出する請求項7に記載のハウリングキャンセラ。
- 前記マイクの収音信号の周波数を低域と高域とに分ける閾値を設定する閾値設定手段をさらに備え、
前記設定手段は、前記低域に挿入されているノッチフィルタが開放されず、前記高域のノッチフィルタが挿入されている周波数が高いほど、該高域のノッチフィルタの挿入時間を短くするように設定する請求項1に記載のハウリングキャンセラ。
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