DE4313256A1 - Method for suppressing feedback in the case of hall or large-field audio systems and circuit arrangement for carrying out the method - Google Patents

Method for suppressing feedback in the case of hall or large-field audio systems and circuit arrangement for carrying out the method

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Publication number
DE4313256A1
DE4313256A1 DE19934313256 DE4313256A DE4313256A1 DE 4313256 A1 DE4313256 A1 DE 4313256A1 DE 19934313256 DE19934313256 DE 19934313256 DE 4313256 A DE4313256 A DE 4313256A DE 4313256 A1 DE4313256 A1 DE 4313256A1
Authority
DE
Germany
Prior art keywords
m2
microphone
microphones
characterized
circuit arrangement
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.)
Withdrawn
Application number
DE19934313256
Other languages
German (de)
Inventor
Michael Walker
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Alcatel SEL AG
Original Assignee
Alcatel SEL AG
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 Alcatel SEL AG filed Critical Alcatel SEL AG
Priority to DE19934313256 priority Critical patent/DE4313256A1/en
Publication of DE4313256A1 publication Critical patent/DE4313256A1/en
Withdrawn legal-status Critical Current

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Classifications

    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04RLOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R5/00Stereophonic arrangements
    • H04R5/027Spatial or constructional arrangements of microphones, e.g. in dummy heads
    • HELECTRICITY
    • H03BASIC ELECTRONIC CIRCUITRY
    • H03GCONTROL OF AMPLIFICATION
    • H03G3/00Gain control in amplifiers or frequency changers without distortion of the input signal
    • H03G3/20Automatic control
    • H03G3/30Automatic control in amplifiers having semiconductor devices
    • H03G3/32Automatic control in amplifiers having semiconductor devices the control being dependent upon ambient noise level or sound level

Abstract

In an audio system having an adaptively controllable compander and a microphone picking up interfering noise, the signals of which are used for controlling the characteristic of the compander (3) in order to suppress feedback effects, several microphones (Mi) are installed at a distance from the speaker or transmitting microphone (M1) at locations at which a higher sound pressure occurs or can be expected due to direct radiation, reflection, interference or room resonances or echoes and the compander characteristic is displaced in the direction of higher attenuation in dependence on the microphone signal level (ni) of the microphones (Mi). <IMAGE>

Description

The present invention relates to a method for Suppressing feedback in hall or Large field sound systems and a circuit arrangement for Execution of the method according to the preamble of claim 1 or claim 5.

Such a method and a suitable one Circuit arrangement is known from DE-A 37 24 346. in the Companders are those delivered by a speaker microphone Signals, hereinafter referred to as transmission signals, insofar as they are above a Setpoint, compressed to a uniform signal level, as far as they have the nominal value, maximally amplified, and, if so they are below the setpoint, expands. The compander characteristic LU2 = f (LU1) has a very steep expansion area and one flat compression area. By feedback of the output signals of the compander over a low pass or one for the language area  permeable band filter to the entrance of the compander can Characteristic shifted towards higher damping values and / or the Characteristic control in the expander area can be changed. Furthermore the characteristic curve control takes place e.g. B. in public address or on Train stations, etc., depending on through a microphone received noise or echoes. This will Overrides that can lead to feedback whistling avoided. In addition, the reverberation is suppressed or strong diminished.

Although the method and this circuit arrangement in the Practice has proven, can in exceptional cases with extreme Feedback, apparently as a result of resonance or Interference of the existing sound and reflection waves, disturbing feedback vibrations occur.

From DE-PS 29 31 604 is still a noise compensated Microphone circuit known, with the help of which it is possible to call noisy rooms from or on airplanes. Here two closely adjacent microphones are provided, by which is the one with the useful signal, so z. B. the Speaker is facing and the other microphone in this opposite direction is arranged. By Switching the two microphones against each other is supposed to Ambient noise can be compensated. In addition, at any time Adaptation to a disturbance situation that is not constant over time to be able to make while maintaining the narrow allocation of two microphones or so-called double microphones in the signal branch of the transmitter microphone an adjusting resistor and in the signal branch of the other microphones a volume control is provided. Furthermore the microphone amplifier of the transmitter microphone works on the output side  with an electro-acoustic or electro-optical Noise indicator together. The optimal possible adjustment is to be carried out by the user himself.

The object of the present invention is therefore to be achieved when using the known method mentioned at the beginning and the known circuit arrangement disturbing feedback phenomena suppress even under very unfavorable environmental conditions and Z. B. at train stations or sports fields, the reverberation as possible largely eliminate.

This problem is solved by the in the characterizing part of claim 1 or of claim 5 specified measures. This will make places where stronger acoustic vibrations occur, in the Compander control included. This will cause a wobble and prevents resonance formation, so that even under extreme unfavorable spatial conditions or space conditions none annoying feedback occur more.

According to an advantageous development of the invention, one Several microphones can be spatially distributed. This additional microphones are conveniently placed where one higher sound level is to be expected if the hall or Change environmental conditions. That can happen in a hall. Legs different seating, different line-up, that Introducing or removing display walls etc. Can outdoors this is mainly due to different wind speeds enter.

Further advantageous details of the invention are in the Subclaims specified and below using the in the Drawing illustrated embodiments described. It demonstrate:  

Fig. 1 basic possibilities of arranging the microphones in a hall with a microphone unit and a PA system and

Fig. 2 is a block diagram of a circuit arrangement of the PA system.

In the dargestellen in Fig. 1 Hall PA system 1 is denoted by M1, a transmitter or speaker microphone. The transmission signal x (t) output by the transmission microphone M1 is present at the input 2 of a compander 3 . The output signal y (t) of the compander 3 is given via an amplifier 4 to speakers 5.1 to 5.5 , each speaker having an output amplifier 6.1 to 6.5 connected upstream. The amplification factor of the final amplifiers 6. X can preferably be set separately and switched on and off.

An adaptively controllable compander is used as compander 3 . With this, the transmission signal x (t), as far as it lies above a setpoint, is compressed to a uniform level, as far as it has a setpoint, amplified to a maximum, and as far as it is below the setpoint, expanded. The companding characteristic curve LU2 = f (LU1) has a steep expansion area 26 and a flat compression area 27 , as can be seen from the diagram shown in FIG. 2. By returning the output signal y (t) via a low-pass filter or a band filter to the control input 11 of the compander 3 , the compander characteristic curve can be shifted and, if necessary, the slope of the characteristic curve in the expander area 26 can be changed. In addition, the characteristic curve can be shifted as a function of received signals z (t), which are likewise applied to the control input 11 .

In the present case, the received signal z (t) is made up of several Microphone signals n2 (t), n3 (t), n4 (t) and n5 (t) from at a distance from Transmitter microphone M1 arranged microphones M2, M3, M4 and M5 derived.

In order to suppress disturbing feedback such as whistling occurring in a hall, the microphones M2, M3, M4 and M5 are installed in places where a higher sound pressure due to direct radiation of sound waves from disturbing sound sources, e.g. B. occurs from at least one of the speakers 5.1 to 5.5 and / or from reflections and / or room resonances and / or echoes occurring in the hall or is to be expected on the basis of measurements or calculations etc.

For example, the microphone M3 is from the transmitter microphone M1 directed away and pointing towards the inclusion of a general Noise level expediently a spherical characteristic.

The microphone M4 mainly faces the speaker 5.5 and partially the speaker 5.4 and expediently has a suitable directional characteristic.

The microphone M5 faces a wall 7 , from which reflections are generally to be expected. It can have a directional characteristic or preferably a spherical characteristic.

A plurality of microphones M2 / 1, M2 / 2 and M2 / 3 are provided for the reflections emanating from a ceiling 8 . Here is z. B. the microphone M2 / 2 provided at a location where a higher sound pressure at z. B. normally occupied hall occurs. The microphones M2 / 1 and M2 / 3 are installed in the same area, but in places with lower sound pressure. However, these places are those where a higher sound pressure occurs when the room occupancy z. B. deviates from normal occupancy.

In FIG. 2, for explaining the superimposition of two wave trains A and B in the region of the microphones M2 / 1 represented M2 / 2, and M2 / 3. Here, a dashed line means a wave trough, to which index 0 is assigned, and the solid line designated with index 1 means a wave crest. As can be seen, the microphone M2 / 2 is located in the area of the intersection of the wave crests or wave troughs. The highest sound pressures therefore occur at this location. The microphone M2 / 2 is in the area of the intersection of the trough of one wave train A₀ or B₀ and wave crest of the other wave train B₁ or A₁, so that theoretically the sound pressure becomes 0. The microphone M2 / 1 is in an intermediate range between the maximum and minimum values.

It can be seen that when the direction of the wave trains changes A and B the microphone M2 / 2 no longer in the range of the maximum value and the microphone M2 / 3 no longer in the range of the minimum value lies; however, the microphone M2 / 1 can be in the range of the maximum value lie.

The output signals n2 / 1, n2 / 2 and n2 / 3 of the microphones M2 / 1, M2 / 2 and M2 / 3 are input to a summer 9 . The sum signal n2 (t) output by this is input to an integrating element 10 with the microphone signals n3 (t), n4 (t) and n5 (t). This advantageously has a short rise time constant and a long fall time constant. For example, the former is approximately 3 to 20 msec, preferably approximately 6 to 12 msec and in particular approximately 10 msec and the second is approximately 40 to 80 msec, in particular approximately 65 msec. The transfer function of the integrator 10 is sufficient for. B. following formula:

With
T i = interval for increasing voltage
T d = interval for falling voltage

The output signal z (t) of the integrator 10 is applied to the control input 11 of the compander 3 and thus at high, z. B. above a certain threshold level of z (t), the compander characteristic in the diagram shown in FIG. 2 is shifted to the right in the direction of higher damping. Since a speaker adapts to this situation with loud ambient noises by increasing his speech volume, good speech intelligibility is achieved in spite of higher attenuation with sufficient suppression of feedback phenomena.

When using the invention, it can also with strong excitation, for. B. when changing speakers, there is no feedback that leads to a Lead self-excitement. A feedback whistle, often only can be eliminated by switching off the sound system therefore definitely prevented.  

According to the basic circuit diagram shown in FIG. 2, each microphone M2 / 1, M2 / 2, M2 / 3, M3 and M4 is followed by an adjustable amplifier V2 / 1, V2 / 2, V2 / 3, V3 and V4. The output signals of the same are connected to the summer 9 . The magnitude of the output sum signal n2 (t) is then formed and the value obtained is fed to an integrator 10.2 .

Each microphone signal n3 (t) and n4 (t) of the microphones M3 and M4 is amplified via an adjustable amplifier V3 and V4, respectively, and the signal is supplied to an integrating element 10.3 and 10.4 after the amount has been formed.

The level output by the integrators 10.2 , 10.3 and 10.4 , namely the integrated mean values n2, n3 and n4, are separately input to a threshold or maximum value detector MAX. If one of the integrated mean values n2, n3, n4 exceeds the maximum value, the maximum value detector MAX outputs a control terminal n max to the control input 11 of the compander 3 and, according to the value of the control signal n max, a shift of the compander characteristic in the direction of higher damping, ie a shift of the characteristic curve to the right.

The microphones M2 / i, M3, M4, M5 assigned are expedient adjustable amplifier Vi integrated into the microphones. Each microphone Mi or amplifier Vi can advantageously be used preferably assigned adjustable frequency or band filter, be integrated in it in particular. This is an adjustment to the sources of interference or disturbing sound waves to be recorded possible and an adaptation of the sound system different conditions in the environment guaranteed.

Claims (11)

1. A method for suppressing feedback in hall or large-field PA systems, etc., which have a transmission branch with at least one transmission microphone and a transmission amplifier, a reception branch with a noise-receiving microphone and a reception amplifier, several loudspeakers for emitting the transmission signal, and an adaptively controllable one Compander, the points of use of the compression and expansion of which are changed as a function of transmission, echo and noise signals in that these signals are determined and control signals are generated in accordance with the level used for dynamic compander control by changing and / or shifting the characteristic of the compander are characterized in that a microphone (M2, M3, M4, at a distance from the transmitting microphone (M1) at several locations where a higher sound pressure due to light radiation, reflections, interference or room resonances or echoes occur or is to be expected. M5) is installed so that, separately from one another, the microphone signals (ni (t)) are amplified by an amplifier (Vi) assigned to each microphone (M2, M3, M4, M5) and then the amount of amplified signals (| ni ( t) | are formed) and is fed via a respective integrator (10 i) to a common maximum value detector (mAX), the maximum value detector (mAX) if a predetermined maximum value (n max) outputs such a control signal to the compandor (3), that its characteristic curve (LU2 = f (LU1)) is changed and / or shifted in such a way that the damping values become so large that no feedback occurs or any feedback that occurs is reduced to non-disturbing values.
2. The method according to claim 1, characterized in that adjustable amplifiers (Vi) are used become.
3. The method according to claim 1 or 2, characterized in that at one or more of the locations in addition to the one microphone (M2, M3, M4, M5) one or more additional microphones (M2 / 1, M2 / 2, M2 / 3) in two or three dimensions distributed to be arranged such that the one or more Microphones (M2 / 1, M2 / 2, M2 / 3) are located in such places where higher sound levels due to changes in the state of the environment occur or can occur that the microphone signals (n2 / 1 (t), n2 / 2 (t), n2 / 3 (t)) separately amplified and then added and then the sum signal (n2 (t)) obtained after Integrated amount formation and the maximum value detector (MAX) is forwarded.
4. The method according to claim 1 to 3, characterized in that when available predominantly in one A microphone directed towards this source of interference (M4) is used, which is a more pronounced directional characteristic owns than the other microphones.  
5. Circuit arrangement for carrying out the method according to one of claims 1 to 4 with an adaptively controllable compander, the points of use of the compression and expansion can be changed as a function of transmission, echo and interference signals, characterized in that they have a totalizer or maximum value detector (MAX ) with several inputs for connecting several microphones (M2, M3, M4, M5), the output of which is connected to the control input ( 11 ) of the compander ( 3 ).
6. Circuit arrangement according to claim 4, characterized in that it has a summer ( 9 ) with a plurality of inputs for connecting a plurality of microphones (M2 / 1, M2 / 2, M2 / 3), the output of which is connected to an input of the maximum value detector (MAX) is.
7. Circuit arrangement according to claim 4 or 5, characterized in that in the microphones (M1, M2, M3, M4, M5) an adjustable preamplifier (Vi) is integrated.
8. Circuit arrangement according to claim 4, 5 or 6, characterized in that in the microphones (Mi) adjustable frequency range or band filter is integrated.
9. Circuit arrangement according to claim 4 to 7, characterized in that the maximum value detector (MAX) or one or more integrating elements ( 10. i) is connected upstream, which has a short rise time and a long fall time .
10. Circuit arrangement according to claim 8, characterized in that the rise time is about 6 to 12 msec, in particular about 10 msec and the fall time about 40 to 80 msec, is in particular about 65 msec.
11. Circuit arrangement according to claim 8 or 9, characterized in that the transfer function (f (t)) of the integrating elements ( 10 i) satisfies the following conditions: With
T i = interval for increasing voltage
T d = interval for falling voltage.
DE19934313256 1993-04-23 1993-04-23 Method for suppressing feedback in the case of hall or large-field audio systems and circuit arrangement for carrying out the method Withdrawn DE4313256A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
DE19934313256 DE4313256A1 (en) 1993-04-23 1993-04-23 Method for suppressing feedback in the case of hall or large-field audio systems and circuit arrangement for carrying out the method

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DE19934313256 DE4313256A1 (en) 1993-04-23 1993-04-23 Method for suppressing feedback in the case of hall or large-field audio systems and circuit arrangement for carrying out the method

Publications (1)

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DE4313256A1 true DE4313256A1 (en) 1994-10-27

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19611548A1 (en) * 1996-03-23 1997-09-25 Sel Alcatel Ag Method and circuit arrangement for improving the transmission properties of an echo transmission line in a telecommunications network
DE19943872A1 (en) * 1999-09-14 2001-03-15 Thomson Brandt Gmbh Device for adjusting the directional characteristic of microphones for voice control
WO2007020104A1 (en) * 2005-08-18 2007-02-22 Stamer Musikanlagen Gmbh Device for reproducing audio signals

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19611548A1 (en) * 1996-03-23 1997-09-25 Sel Alcatel Ag Method and circuit arrangement for improving the transmission properties of an echo transmission line in a telecommunications network
US5909489A (en) * 1996-03-23 1999-06-01 Alcatel Alsthom Compagnie Generale D'electricite Method of and circuit arrangement for improving the transmission properties of an echo affected transmission link in a telecommunications network
DE19943872A1 (en) * 1999-09-14 2001-03-15 Thomson Brandt Gmbh Device for adjusting the directional characteristic of microphones for voice control
WO2007020104A1 (en) * 2005-08-18 2007-02-22 Stamer Musikanlagen Gmbh Device for reproducing audio signals

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