WO2011090386A1 - Location dependent feedback cancellation - Google Patents

Location dependent feedback cancellation Download PDF

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Publication number
WO2011090386A1
WO2011090386A1 PCT/NO2010/000021 NO2010000021W WO2011090386A1 WO 2011090386 A1 WO2011090386 A1 WO 2011090386A1 NO 2010000021 W NO2010000021 W NO 2010000021W WO 2011090386 A1 WO2011090386 A1 WO 2011090386A1
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WO
WIPO (PCT)
Prior art keywords
sound
captured
area
feedback
different positions
Prior art date
Application number
PCT/NO2010/000021
Other languages
French (fr)
Inventor
Morgan KJØLERBAKKEN
Ines Hafizovic
Andreas Holm
Johannes Alming Daleng
Original Assignee
Squarehead Technology As
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Squarehead Technology As filed Critical Squarehead Technology As
Priority to PCT/NO2010/000021 priority Critical patent/WO2011090386A1/en
Publication of WO2011090386A1 publication Critical patent/WO2011090386A1/en

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R27/00—Public address systems
    • 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
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R2430/00—Signal processing covered by H04R, not provided for in its groups
    • H04R2430/20—Processing of the output signals of the acoustic transducers of an array for obtaining a desired directivity characteristic
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R29/00—Monitoring arrangements; Testing arrangements
    • H04R29/007—Monitoring arrangements; Testing arrangements for public address systems
    • 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
    • H04R3/005—Circuits for transducers, loudspeakers or microphones for combining the signals of two or more microphones

Definitions

  • the present invention concerns controlling captured and recorded sound. More specifically the invention concerns a method and system for cancelling feedback from captured sound at different positions in an area.
  • one or more loudspeakers used in a PA system When performing a conference or meeting, typically one or more loudspeakers used in a PA system will address an audience of several participant located in an area in front of the loudspeakers. This area may for instance be a room with specific characteristic acoustical properties.
  • the feedback (resonate) frequency is determined by both microphone/loudspeaker system used (PA system), and the room acoustics where they are used. Since the room acoustic resonant frequencies differ depending on where you are in a room, the feedback frequencies will also differ depending on different positions in the room where audio is captured.
  • PA system microphone/loudspeaker system used
  • feedback destroyers or feedback eliminators
  • a common way to avoid feedback is to use notch filters or frequency-shifting.
  • Adaptive feedback cancellers need however a certain time to detect feedback and to apply the right type of action. This will give a critical time gap where the resonant frequencies are allowed to grow and the result will be an unwanted high-pitched squealing noise.
  • the present invention will ensure that the feedback effects are set for each position in advanced, such that no time delay occur before the feedback cancelling effects are activated.
  • the present invention will only apply anti feedback measures to positions in an area or room where it is required. The result is an overall much better audio quality.
  • the present invention is described by a method for performing position dependent feedback cancelation, when capturing sound in a restricted area. This is achieved by performing the following steps:
  • the invention also comprises a system for performing position dependent feedback cancellation.
  • Figure 1 shows the system for controlling a microphone array
  • Figure 2 illustrates how the system works.
  • the present invention comprises a method for performing position dependent feedback cancelation, when capturing sound in a restricted area, e.g. a room.
  • the first step is to set up the system by assessing which locations or positions that give rise to feedback. For doing this, sound is played on loudspeakers comprised located in the area.
  • the next step is to capture sound at different positions in the area. This may be performed manually by pointing a directive microphone at different positions in the area and then assess the output either automatically or manually.
  • a preferred method is however to use a microphone array for capturing sound at different areas or in a room. By performing beam forming of the output form a microphone array, sound can be captured from different positions in the area.
  • Figure 1 shows an example where an audience of people 10 is located in a room with a microphone array 20 capturing sound from the audience.
  • Different positions of the room are scanned by beam forming the output of the microphone array, thus enabling position specific capturing of sound.
  • Captured sound from different positions is then assessed with regards to feedback.
  • Feedback information as a function of position is then stored in a memory.
  • the feedback information may comprise type of feedback and feedback frequencies at each positions in an area. It may also comprise information of what anti feedback audio effect to use when capturing sound from a specific position. Input to this information is the position and type of feedback from this location.
  • the next step is to capture and record sound at different positions in the room, and then apply anti feedback audio effect measures on the captured sound by looking up the relevant information in said memory, i.e. feedback information corresponding to specific positions.
  • the feedback can then be cancelled from one or more specific input positions where sound is captured from.
  • One or more audio effects can be added to a specific position in order to correct or shape the output signal.
  • these effects are: high/low pass filters; band pass filters; high/low shelf filters; notch filters; peak filters; peak limiters; weighting functions (for changing the beam pattern); gain adjustments; sub array
  • the individual audio effects to use for each position can either be set up manually, which might be preferred by a skilled audio engineer, or by the system itself where the system automatically sweep through the room and applies the necessary audio effects, e.g. by applying notch filters.
  • a convenient way to implement the present invention is to divide the room or area into cells (sectors), as indicated in figure 1, and then apply certain effects to one or more cells.
  • the microphone array is then beamformed such that sound from each cell is captured and assessed.
  • a cell can be in one, two or three dimensions.
  • the system is dependent on the radius or an angle.
  • the system is dependent on x and y coordinates or angle and radius.
  • the system is dependent on x, y and z coordinates or two angles (theta, phi) and radius.
  • Figure 2 illustrate how the system works when using a microphone array as the sound capturing device. The arrows on the left indicate the output from a
  • the system receives steering coordinates from an input device, instructing it to focus and capture sound from one or more specific locations.
  • the input device may be a graphical user interface showing a representation of the area.
  • This representation may be a picture, or live video of the area.
  • the latter is a user friendly way of using the system for a speaker addressing an audience, and where for instance a person in the audience has a question.
  • the speaker may then find the person or the position where the person is located on a touch screen, and click there for instructing the system to focus and apply the inventive method corresponding to that position.
  • the input device may also be an audio and/or video tracking system.
  • An audio tracking system may for instance focus on a position in an audience where speech is detected.
  • a video tracking system may for instance track and focus on a ball in a play field.
  • the system When the system has received the input position(s), it will use this information to beamform the output from the microphone array, such that the focus of captured sound is at that location. It will also use this position information to look up from said memory, the corresponding audio effect to use on the sound captured from the specific location. A suitable audio effect is then selected and applied on the beamformed signal, resulting in an optimized output where feedback is cancelled.
  • the present invention will ensure that no time delay occur before feedback cancelling effects are activated, and the overall sound quality is better than prior art.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Health & Medical Sciences (AREA)
  • General Health & Medical Sciences (AREA)
  • Otolaryngology (AREA)
  • Circuit For Audible Band Transducer (AREA)

Abstract

Method and system for performing position dependent feedback cancellation, when capturing sound in a restricted area. The area is scanned by capturing sound emitted from loudspeakers, and where this is done at different positions. The captured sound is assessed with regards to feedback problems at the different positions, and this feedback information is stored in a memory. Feedback audio effect measures are the applied on captured sound from specific input positions, and where this is done by looking up in said memory relevant feedback information corresponding to said input positions.

Description

LOCATION DEPENDENT FEEDBACK CANCELLATION
Technical field
The present invention concerns controlling captured and recorded sound. More specifically the invention concerns a method and system for cancelling feedback from captured sound at different positions in an area.
Prior art
When performing a conference or meeting, typically one or more loudspeakers used in a PA system will address an audience of several participant located in an area in front of the loudspeakers. This area may for instance be a room with specific characteristic acoustical properties.
Acoustical feedback will occur when a sound loop between a microphone and a loudspeaker have a gain greater than 1.
The feedback (resonate) frequency is determined by both microphone/loudspeaker system used (PA system), and the room acoustics where they are used. Since the room acoustic resonant frequencies differ depending on where you are in a room, the feedback frequencies will also differ depending on different positions in the room where audio is captured.
There are several feedback cancelling systems on the market. Some of these are called "feedback destroyers" or "feedback eliminators".
A common way to avoid feedback is to use notch filters or frequency-shifting.
These anti feedback methods are either set in advance or adaptively set in real-time. Adaptive feedback cancellers need however a certain time to detect feedback and to apply the right type of action. This will give a critical time gap where the resonant frequencies are allowed to grow and the result will be an unwanted high-pitched squealing noise.
The present invention will ensure that the feedback effects are set for each position in advanced, such that no time delay occur before the feedback cancelling effects are activated.
Normally when you calibrate a system with predefined notch filters you need to apply notch filters for all (major) resonant frequencies in the room (or the part of the room where a microphone is to be used). This will result in that a lot of filters are used all the time, which makes a significant reduction in total audio quality. The same applies when frequency shift is used. Frequency shift is applied to the signal even if it is not required.
The present invention will only apply anti feedback measures to positions in an area or room where it is required. The result is an overall much better audio quality. Summary
The present invention is described by a method for performing position dependent feedback cancelation, when capturing sound in a restricted area. This is achieved by performing the following steps:
- outputting sound on a PA system in the area;
- scanning the area with a sound capturing device directed or located at different positions in the area;
- assessing captured sound with regards to feedback of sound at the different positions, and storing in a memory feedback information as a function of position, and
- applying anti feedback audio effect measures on captured sound only at specific input positions the sound is to be captured from.
The invention also comprises a system for performing position dependent feedback cancellation.
Main claims define main features of the invention, and dependent claims define further feature of the invention.
Detailed description
In the following, the invention will be described in detail with reference to the drawings where:
Figure 1 shows the system for controlling a microphone array, and
Figure 2 illustrates how the system works.
As said, the present invention comprises a method for performing position dependent feedback cancelation, when capturing sound in a restricted area, e.g. a room.
For achieving this, different steps are performed. The first step is to set up the system by assessing which locations or positions that give rise to feedback. For doing this, sound is played on loudspeakers comprised located in the area.
The next step is to capture sound at different positions in the area. This may be performed manually by pointing a directive microphone at different positions in the area and then assess the output either automatically or manually. A preferred method is however to use a microphone array for capturing sound at different areas or in a room. By performing beam forming of the output form a microphone array, sound can be captured from different positions in the area.
Figure 1 shows an example where an audience of people 10 is located in a room with a microphone array 20 capturing sound from the audience.
Different positions of the room are scanned by beam forming the output of the microphone array, thus enabling position specific capturing of sound.
Captured sound from different positions is then assessed with regards to feedback. Feedback information as a function of position is then stored in a memory. The feedback information may comprise type of feedback and feedback frequencies at each positions in an area. It may also comprise information of what anti feedback audio effect to use when capturing sound from a specific position. Input to this information is the position and type of feedback from this location.
The next step is to capture and record sound at different positions in the room, and then apply anti feedback audio effect measures on the captured sound by looking up the relevant information in said memory, i.e. feedback information corresponding to specific positions. The feedback can then be cancelled from one or more specific input positions where sound is captured from.
One or more audio effects can be added to a specific position in order to correct or shape the output signal. Among these effects are: high/low pass filters; band pass filters; high/low shelf filters; notch filters; peak filters; peak limiters; weighting functions (for changing the beam pattern); gain adjustments; sub array
configuration; frequency shift, and echo filters. Other known effects and/or filters are also applicable.
The individual audio effects to use for each position can either be set up manually, which might be preferred by a skilled audio engineer, or by the system itself where the system automatically sweep through the room and applies the necessary audio effects, e.g. by applying notch filters.
A convenient way to implement the present invention is to divide the room or area into cells (sectors), as indicated in figure 1, and then apply certain effects to one or more cells. The microphone array is then beamformed such that sound from each cell is captured and assessed.
A cell can be in one, two or three dimensions. In one dimension, the system is dependent on the radius or an angle. In two dimensions, the system is dependent on x and y coordinates or angle and radius. In three dimensions, the system is dependent on x, y and z coordinates or two angles (theta, phi) and radius. Figure 2 illustrate how the system works when using a microphone array as the sound capturing device. The arrows on the left indicate the output from a
microphone array. The system receives steering coordinates from an input device, instructing it to focus and capture sound from one or more specific locations.
The input device may be a graphical user interface showing a representation of the area. This representation may be a picture, or live video of the area. The latter is a user friendly way of using the system for a speaker addressing an audience, and where for instance a person in the audience has a question. The speaker may then find the person or the position where the person is located on a touch screen, and click there for instructing the system to focus and apply the inventive method corresponding to that position.
The input device may also be an audio and/or video tracking system. An audio tracking system may for instance focus on a position in an audience where speech is detected. A video tracking system may for instance track and focus on a ball in a play field.
When the system has received the input position(s), it will use this information to beamform the output from the microphone array, such that the focus of captured sound is at that location. It will also use this position information to look up from said memory, the corresponding audio effect to use on the sound captured from the specific location. A suitable audio effect is then selected and applied on the beamformed signal, resulting in an optimized output where feedback is cancelled.
The present invention will ensure that no time delay occur before feedback cancelling effects are activated, and the overall sound quality is better than prior art.

Claims

1. A method for performing position dependent feedback cancellation, when capturing sound in a restricted area,
c h a r a c t e r i z e d i n performing the following steps:
- outputting sound on a PA system in the area;
- scanning the area with a sound capturing device directed or located at different positions in the area;
- assessing captured sound with regards to feedback of sound at the different positions, and storing in a memory feedback information as a function of position, and
- applying anti feedback audio effect measures on captured sound only at specific input positions the sound is to be captured from by looking up in said memory relevant feedback information corresponding to said input positions.
2. A method according to claim 1 , where the restricted area is a room.
A method according to claim 1, where the sound capturing device is a microphone array, and where different positions of the area is scanned by beamforming the output of the microphone array.
A method according to claim 1 , where the assessing of captured sound comprises analysing which frequencies at the different positions that are causing feedback.
A method according to claim 1, where the assessing of captured sound comprises assessing which type of signal changing means to apply to the output signal of the sound captured at the different positions.
A method according to claim 1 and 5, where which type of signal changing means to apply to a specific position where sound is captured from is stored in a table in the memory.
7. A method according to claim 1, where the position the sound is to be
captured from is a corresponding input position on a graphical user interface showing the area.
8. A method according to claim 7, where the graphical user interface display a picture of the area.
9. A method according to claim 7, where the graphical user interface display a live video of the area.
10. A method according to claim 1, where the position the sound is to be
captured from is an input position selected by an audio and/or video tracking system.
1 1. A method according to claim 1 , where the input position the sound is to be captured from is looked up in the memory together with the relevant audio effect to apply to the specific position.
12. System for performing position dependent feedback cancelation, when
capturing sound in an area,
c h a r a c t e r i z e d i n comprising means for:
- outputting sound on a PA system in the area;
- scanning the area with a sound capturing device directed or located at different positions in the area;
- assessing captured sound with regards to feedback of sound at the different positions, and storing feedback information in a memory as a function of position, and
- applying anti feedback audio effect measures on captured sound only at specific input positions the sound is to be captured from.
PCT/NO2010/000021 2010-01-19 2010-01-19 Location dependent feedback cancellation WO2011090386A1 (en)

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PCT/NO2010/000021 WO2011090386A1 (en) 2010-01-19 2010-01-19 Location dependent feedback cancellation

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Application Number Priority Date Filing Date Title
PCT/NO2010/000021 WO2011090386A1 (en) 2010-01-19 2010-01-19 Location dependent feedback cancellation

Publications (1)

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0843502A1 (en) * 1996-11-13 1998-05-20 Yamaha Corporation Howling detection and prevention circuit and a loudspeaker system employing the same
CA2413217A1 (en) * 2002-11-29 2004-05-29 Mitel Knowledge Corporation Method of acoustic echo cancellation in full-duplex hands free audio conferencing with spatial directivity
WO2007037700A1 (en) * 2005-09-30 2007-04-05 Squarehead Technology As Directional audio capturing
EP2086249A2 (en) * 2008-01-31 2009-08-05 Yamaha Corporation Howling suppression apparatus and computer readable recording medium

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0843502A1 (en) * 1996-11-13 1998-05-20 Yamaha Corporation Howling detection and prevention circuit and a loudspeaker system employing the same
CA2413217A1 (en) * 2002-11-29 2004-05-29 Mitel Knowledge Corporation Method of acoustic echo cancellation in full-duplex hands free audio conferencing with spatial directivity
WO2007037700A1 (en) * 2005-09-30 2007-04-05 Squarehead Technology As Directional audio capturing
EP2086249A2 (en) * 2008-01-31 2009-08-05 Yamaha Corporation Howling suppression apparatus and computer readable recording medium

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