DE19923601C1 - Echo compensation device for hands-free telephone, uses calibration signal for providing coefficients for echo replicator simulating loudspeaker-room-microphone system - Google Patents

Echo compensation device for hands-free telephone, uses calibration signal for providing coefficients for echo replicator simulating loudspeaker-room-microphone system

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Publication number
DE19923601C1
DE19923601C1 DE19923601A DE19923601A DE19923601C1 DE 19923601 C1 DE19923601 C1 DE 19923601C1 DE 19923601 A DE19923601 A DE 19923601A DE 19923601 A DE19923601 A DE 19923601A DE 19923601 C1 DE19923601 C1 DE 19923601C1
Authority
DE
Germany
Prior art keywords
microphone
loudspeaker
echo
calibration signal
room
Prior art date
Legal status (The legal status 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 status listed.)
Expired - Lifetime
Application number
DE19923601A
Other languages
German (de)
Inventor
Matthias Waldorf
Original Assignee
Matthias Waldorf
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 Matthias Waldorf filed Critical Matthias Waldorf
Priority to DE19923601A priority Critical patent/DE19923601C1/en
Application granted granted Critical
Publication of DE19923601C1 publication Critical patent/DE19923601C1/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • GPHYSICS
    • G10MUSICAL INSTRUMENTS; ACOUSTICS
    • G10LSPEECH ANALYSIS OR SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING; SPEECH OR AUDIO CODING OR DECODING
    • G10L21/00Processing of the speech or voice signal to produce another audible or non-audible signal, e.g. visual or tactile, in order to modify its quality or its intelligibility
    • G10L21/02Speech enhancement, e.g. noise reduction or echo cancellation
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04MTELEPHONIC COMMUNICATION
    • H04M1/00Substation equipment, e.g. for use by subscribers; Analogous equipment at exchanges
    • H04M1/60Substation equipment, e.g. for use by subscribers; Analogous equipment at exchanges including speech amplifiers
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04MTELEPHONIC COMMUNICATION
    • H04M9/00Interconnection arrangements not involving centralised switching
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04MTELEPHONIC COMMUNICATION
    • H04M9/00Interconnection arrangements not involving centralised switching
    • H04M9/08Two-way loud-speaking telephone systems with means for suppressing echoes or otherwise conditioning for one or other direction of traffic
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04RLOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R3/00Circuits for transducers, loudspeakers or microphones
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04RLOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R5/00Stereophonic arrangements
    • H04R5/04Circuit arrangements, e.g. for selective connection of amplifier inputs/outputs to loudspeakers, for loudspeaker detection, or for adaptation of settings to personal preferences or hearing impairments

Abstract

The invention describes an arrangement for compensating for echoes which arise in a system which comprises at least one loudspeaker, an echo-affected transmission space and at least one microphone (loudspeaker-space-microphone system) and a time-variant impulse response, with an echo replicator for generating an Echo replica by replicating the time-variant impulse response of the loudspeaker-room microphone system by supplying corresponding time-variant coefficients, with a device for subtracting the output signal of the echo replicator from the output signal of the loudspeaker-room microphone system, with a device for generating a calibration signal a device for superimposing the calibration signal with the input signal of the loudspeaker-room-microphone system and with a calibration signal detection device for generating the said coefficients for the echo replicator from the calibration signal and the output signal of the sound speaker room microphone system.

Description

The invention relates to an arrangement described in the preamble of claim 1 Arrangements of this type are used for echo cancellation.

Hands-free devices are an important area of application. In a hands-free device namely the problem arises that the voice signal reproduced via a loudspeaker of the remote subscriber is recorded by the microphone of the hands-free device and, in order to delay the running time of the system, is retransmitted to the remote subscriber. This effect is perceived as an echo or reverberation. An echo canceller more or less completely prevents this effect. Fig. 1 shows the basic structure of such a system. The signal from the distant subscriber is not only supplied to the loudspeaker 1 , but also to an echo replicator 5 . This echo replicator should replicate the signal response of the loudspeaker-room-microphone system (LRMS) 3 as precisely as possible. The output signal of the echo replicator 5 is subtracted from the output signal of the microphone 2 in the subtraction unit 6 . Ideally, only the speech signal of the speaker 4 is then present at the output of the subtraction unit 6 .

As a rule, the signal response of the LRMS changes constantly. The echo replicator 5 must therefore be constantly adjusted in accordance with the properties of the LRMS. In the case of a linear LRMS (which is usually a good approximation), the echo replica has a shape as shown in FIG. 2. The individual values of the input signal vector 10 are multiplied by the (time-variant) coefficients C k and then summed in the adder 11 . The number of required coefficients depends on the maximum duration of the echoes to be compensated. The known methods determine these coefficients approximately from the microphone and the loudspeaker signal by means of complex numerical methods. Under unfavorable circumstances, these methods are often stable or converge slowly and often only allow incomplete echo compensation.

Further information on the relevant prior art can be found in. P. Dreiseitel, E. Hansler, H. Puder: "Acoustic Echo and Noise Control - A Long Lasting Challenge", Procee EUSIPCO-98, Isle of Rhodes, Greece, September 1998.

In DE 197 14 966 C2, which has a device for the attenuation of the subject matter are Problems described with insufficient or incorrect adaptation of digital echo compensators occur. There it is stated that such compensators as adaptive fil  ter that are designed for the transfer function of the loudspeaker room microphone Systems should reproduce as well as possible. The adaptation of the filter coefficients is only allowed then take place when there is a voice signal from the far end. As soon as the local subscriber also speaks, there is a risk that the echo canceller diverges. Therefore, in the case of two-way communication, the adaptation must be stopped or at least strongly to be slowed down. To remedy this, the patent document mentioned proposed to provide a means for determining the power transmission factor and this among other things to control the adaptation of an adaptive echo canceller to use and thereby improve the adaptation.

The invention has set itself the task of a novel way to time variant to demonstrate the signal response of the loudspeaker-room-microphone system which this replica neither from the voice signal of the distant subscriber nor from that of the local participant is dependent and thereby the state of the art to eliminate the disadvantages.

This object is achieved by the features mentioned in claim 1.

By using a calibration signal according to the invention, the control of the Echo replica no longer responds to the speech signal from the far end instructed and will not affect the voice signal of the local subscriber.

Advantageous developments of the invention are specified in the subclaims.

The invention is explained in more detail below with reference to the drawing:

Fig. 1, the block diagram shows as already mentioned, an echo canceller according to the prior art,

Fig. 2 shows the basic circuit diagram of a known Echoreplikators,

Fig. 3 shows an echo canceller according to an embodiment of the invention.

FIG. 4 shows the circuit for calibration signal detection in the exemplary embodiment from FIG. 3.

Fig. 3 shows an, embodiment of the invention. It is an echo compensator, which allows a very precise determination of the signal response of the loudspeaker room microphone system. A calibration signal 7 is added to the signal from the loudspeaker 1 continuously or temporarily by means of the adder 8 . A calibration signal detector 9 continuously analyzes the microphone signal and thus determines the coefficients C k required for parameterization of the echo replicator 5 . The calibration signal detector can have the structure shown in FIG. 4, for example. The values of the calibration signal vector 12 are passed together with the microphone signal to a number of correlators 13 . The output signals of the correlators then give the desired coefficients for a linear echo replicator.

For this purpose, the calibration signal is advantageously chosen such that the autocorrelation time is greater than the transit time of the echoes to be compensated. A pseudo noise signal is well suited for this. Even if this noise can be perceived by the user 4 , this disadvantage is more than offset by the improved echo cancellation. The calibration signal can also be designed so that the perceptibility is reduced by masking effects. It is also conceivable to use calibration signals that are perceived as being particularly unpleasant.

The invention can also be used advantageously if several microphones or Speakers are used (e.g. for stereo transmission). In this case, each another calibration signal is added to the speaker signal. The cross correlation pro product of these calibration signals should advantageously be within the maximum echo delays disappear. There is a separate echo canceller for each speaker microphone path built up. In this case, very good echo cancellation is possible.

Claims (11)

1. Arrangement for compensating for echoes that arise in a system that comprises at least one loudspeaker ( 1 ), an echo-affected transmission space ( 3 ) and at least one microphone ( 2 ) (loudspeaker-room-microphone system) and a time has a variant impulse response,
with an echo replicator ( 5 ) for generating an echo replica by simulating the time-variant impulse response of the loudspeaker-room-microphone system by supplying corresponding time-variant coefficients (c k ) and
with a device ( 6 ) for subtracting the output signal of the echo replicator from the output signal of the loudspeaker-room-microphone system,
marked by
a device ( 7 ) for generating a calibration signal,
a device ( 8 ) for superimposing the calibration signal with the input signal of the loudspeaker-room-microphone system and
a calibration signal detection device for generating said coefficients (c k ) for the echo replicator ( 5 ) from the calibration signal and the output signal of the loudspeaker-room-microphone system.
2. Arrangement according to claim 1, characterized in that the calibration signal Has an autocorrelation function whose autocorrelation time is at least as long as that longest running time of the echoes to be compensated.
3. Arrangement according to claim 1 or 2, characterized in that the calibration signal is a pseudo noise signal.
4. Arrangement according to one of claims 1 to 3, characterized in that the Ka calibration signal to the input signal of the loudspeaker-room-microphone system constantly is superimposed.
5. Arrangement according to one of claims 1 to 3, characterized in that the potash briersignal the input signal of the loudspeaker-room-microphone system not constantly is superimposed.  
6. Arrangement according to one of claims 1 to 5, characterized in that the Ka The calibration signal is shaped in such a way that it is physiologically perceived as as little disruptive as possible becomes.
7. Arrangement according to claim 6, characterized in that the calibration signal is an Si gnal is its physiological perceptibility through masking effects of the hearing right is induced.
8. Arrangement according to one of claims 1 to 5, characterized in that the Kali briersignal detection device ( 9 ) consists of a number of correlators ( 13 ), de NEN the output signal of the loudspeaker-room-microphone system or that in stages Delayed calibration signal (calibration signal vector) is supplied, the output signals forming the coefficients mentioned for the echo replicator ( 5 ).
9. Arrangement according to claim 8, characterized in that the integration time of Correlators of the change in time of the relevant coefficients is adapted.
10. The arrangement according to claim 9, characterized in that adaptation of the integra tion time of the correlators takes place adaptively.
11. Arrangement according to one of the preceding claims, characterized in
that the loudspeaker-room-microphone system comprises several loudspeakers and several microphones,
that an echo replicator and a calibration signal detection device and a different calibration signal for each echo replicator are seen in front of each speaker microphone path,
the individual calibration signals being orthogonal to one another and such that their cross-correlation disappears.
DE19923601A 1999-05-24 1999-05-24 Echo compensation device for hands-free telephone, uses calibration signal for providing coefficients for echo replicator simulating loudspeaker-room-microphone system Expired - Lifetime DE19923601C1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
DE19923601A DE19923601C1 (en) 1999-05-24 1999-05-24 Echo compensation device for hands-free telephone, uses calibration signal for providing coefficients for echo replicator simulating loudspeaker-room-microphone system

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE19923601A DE19923601C1 (en) 1999-05-24 1999-05-24 Echo compensation device for hands-free telephone, uses calibration signal for providing coefficients for echo replicator simulating loudspeaker-room-microphone system
PCT/EP2000/004674 WO2000072564A2 (en) 1999-05-24 2000-05-23 Echo compensation device

Publications (1)

Publication Number Publication Date
DE19923601C1 true DE19923601C1 (en) 2000-10-05

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Family Applications (1)

Application Number Title Priority Date Filing Date
DE19923601A Expired - Lifetime DE19923601C1 (en) 1999-05-24 1999-05-24 Echo compensation device for hands-free telephone, uses calibration signal for providing coefficients for echo replicator simulating loudspeaker-room-microphone system

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DE (1) DE19923601C1 (en)
WO (1) WO2000072564A2 (en)

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19714966A1 (en) * 1997-04-10 1998-10-15 Siemens Ag Device for reducing attenuation

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4404645A (en) * 1980-08-18 1983-09-13 Elings Virgil B Correlator
JPH0748681B2 (en) * 1989-02-23 1995-05-24 日本電気株式会社 Echo canceller coefficient control method
US5327496A (en) * 1993-06-30 1994-07-05 Iowa State University Research Foundation, Inc. Communication device, apparatus, and method utilizing pseudonoise signal for acoustical echo cancellation
US6496581B1 (en) * 1997-09-11 2002-12-17 Digisonix, Inc. Coupled acoustic echo cancellation system

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19714966A1 (en) * 1997-04-10 1998-10-15 Siemens Ag Device for reducing attenuation
DE19714966C2 (en) * 1997-04-10 1999-04-01 Siemens Ag Device for reducing attenuation

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
DREISEITEL, P. et al.: Acoustic Echo and Noise Control- A Long Lasting Challenge, In: ProceedingsEUSIPCO-98, Isle of Rhodes, Greece, Sept. 1998 *

Also Published As

Publication number Publication date
WO2000072564A3 (en) 2001-07-05
WO2000072564A2 (en) 2000-11-30

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