Method and apparatus for eliminating audio feedback

• US 6,108,427 A
• Filed: 06/04/1997
• Issued: 08/22/2000
• Est. Priority Date: 07/17/1996
• Status: Expired due to Fees

• Current Assignee: American Technology Incorporated (Emerson Electric Company)
• Original Assignee: American Technology Incorporated (Emerson Electric Company)
• Inventors: Bank, Jeevan, Norris, Elwood G.
• Primary Examiner(s): Chang, Vivian
• Application Number:
  US08/868,739
• Time in Patent Office: 1,175 Days
• Field of Search: 381/94.1, 381/77, 381/82, 381/79, 381/93, 381/83, 381/66
• US Class Current: 381/83
• CPC Class Codes: G10K 15/02 Synthesis of acoustic waves synthesis of speech G10L13/00
• CPC Class Codes: H04B 11/00 Transmission systems employing sonic, ultrasonic or infrasonic waves
• CPC Class Codes: H04R 2217/03 Parametric transducers where sound is generated or captured by the acoustic demodulation of amplitude modulated ultrasonic waves
• CPC Class Codes: H04R 23/00 Transducers other than those covered by groups H04R9/00 - H04R21/00 diaphragms for transducers of the distributed-mode type H04R7/045
• CPC Class Codes: H04R 3/02 for preventing acoustic reaction , i.e. acoustic oscillatory feedback specially adapted for hearing aids H04R25/453
• CPC Class Codes: H04R 5/02 Spatial or constructional arrangements of loudspeakers
• CPC Class Codes: H04S 1/002 Non-adaptive circuits, e.g. manually adjustable or static, for enhancing the sound image or the spatial distribution control circuits for electronic adaptation of the sound field H04S7/30

Abstract

The present invention is embodied in a method and apparatus for eliminating audio feedback which includes an active microphone coupled to an amplifier which transmits signals received at the active microphone to a parametric speaker for broadcasting. The apparatus comprises at least one transducer for detecting at least one sonic frequency and generating an electrical signal representative of the at least one sonic frequency, a processor for receiving the electrical signal and generating a first ultrasonic frequency which has modulated thereon the at least one sonic frequency, a parametric demodulator for recovering the at least one sonic frequency from the first ultrasonic frequency, and a speaker for directly emitting the at least one sonic frequency.

Claims

1. A system for eliminating audio feedback, comprising:

at least one speaker member;

at least one microphone means for detecting at least one sonic frequency emitted from the speaker member and for generating an electrical signal representative of the at least one sonic frequency;

processing means coupled to the microphone means for receiving the electrical signal wherein the processing means comprises the following parametric speaker components in which all signals received from the microphone are processed as a single wave form for parametric output through said parametric speaker components;

a) ultrasonic frequency/generating means for generating a first ultrasonic frequency;

b) modulating means coupled to the ultrasonic frequency generating means and the processing means for generating a new wave form electronically which includes the at least one first and second ultrasonic frequency having a difference in value equal to the at least one sonic frequency; and

c) at least one ultrasonic frequency emitter coupled to the modulating means and the speaker member for concurrently propagating from a common emitter face (i) the first ultrasonic frequency and (ii) the at least one second ultrasonic frequency which interacts with the first ultrasonic frequency within a compressible transmission medium to thereby generate the at least one sonic frequency free of audio feedback.

2. The system for eliminating audio feedback as defined in claim 1 wherein the at least one microphone means for detecting the at least one sonic frequency and generating an electrical signal representative of the at least one sonic frequency is comprised of an active microphone.

3. The system for eliminating audio feedback as defined in claim 1 wherein the modulating means further comprises an ultrasonic frequency signal generator which generates and transmits the second ultrasonic frequency to the at least one ultrasonic frequency emitter and to the modulating means, to thereby generate the at least one sonic frequency.

4. The system for eliminating audio feedback as defined in claim 1 wherein the at least one sonic frequency is a live sound source.

5. The system for eliminating audio feedback as defined in claim 4 wherein the live sound source is selected from the group of live sound sources consisting of speech, singing, musical instruments and other sonic sound generating devices.

6. The system for eliminating audio feedback as defined in claim 1 wherein the at least one ultrasonic frequency emitter is comprised of ultrasonic acoustical transducers.

7. A system as defined in claim 1, wherein the modulating means further comprises mixing means for electronically combining the first and second ultrasonic frequencies to form a single new wave form representing the sum of the first and second ultrasonic frequencies, said system including means for transmitting the single new wave form to the common emitter face for propagation into air.

8. A system as defined in claim 1, wherein the modulating means comprises means for amplitude modulating the first ultrasonic frequency with the at least one sonic frequency to generate the second ultrasonic frequency as at least one sideband to the first ultrasonic frequency.

9. The system as defined in claim 8, further comprising filtering means coupled to the amplitude modulating means for eliminating one of the sidebands.

10. The system as defined in claim 1 wherein the ultrasonic frequency generating means (i) generates and transmits the second ultrasonic frequency to the at least one ultrasonic frequency emitter, and (ii) transmits the second ultrasonic frequency to the modulating means and wherein the modulating means includes input means for mixing audible sounds with the second ultrasonic frequency as upper and lower sidebands.

11. A method for eliminating audio feedback from an audio system generating at least one sonic frequency, said method comprising the steps of:

(1) receiving at a microphone the at least one sonic frequency as a total audio signal to be processed at an input of the audio system;

(2) processing the total audio signal, including the at least one sonic frequency by modulating the total audio signal with an ultrasonic carrier frequency to generate a new wave form electronically to thereby prepare it for emission from a parametric speaker; and

(3) emitting the ultrasonic frequency carrier wave combined with the at least one sonic frequency from the parametric speaker without bypassing any portion of the signal to a nonparametric speaker to thereby generate the at least one sonic frequency as an audible sound free of audio feedback.

12. The method for eliminating audio feedback as defined in claim 11 wherein the step of receiving the at least one sonic frequency at an input of the audio system further comprises receiving the at least one frequency at an active microphone.

13. The method for eliminating audio feedback as defined in claim 11 wherein the step of processing the at least one sonic frequency further comprises the step of amplitude modulating the at least one sonic frequency onto the ultrasonic frequency carrier wave.

14. The method for eliminating audio feedback as defined in claim 11 wherein the step of processing the at least one sonic frequency further comprises the steps of concurrently propagating from a common emitter face of the parametric speaker (i) a second ultrasonic wave train having a second ultrasonic frequency and (ii) a first ultrasonic wave train having the ultrasonic frequency carrier wave which interacts with the second ultrasonic wave train within a compressible transmission medium.

15. The method for eliminating audio feedback as defined in claim 14 wherein the step of processing the at least one sonic frequency further comprises the step of electronically combining the first and second ultrasonic wave trains to form a single new electronic wave form.