Active attenuation system with increased dynamic range

• US 4,736,431 A
• Filed: 10/23/1986
• Issued: 04/05/1988
• Est. Priority Date: 10/23/1986
• Status: Expired due to Term

• Current Assignee: Nelson Industries Incorporated (Cummins Incorporated)
• Original Assignee: Nelson Industries Incorporated (Cummins Incorporated)
• Inventors: Bailey, Geoffrey S., Allie, Mark C.
• Primary Examiner(s): Isen, Forester W.
• Application Number:
  US06/922,282
• Time in Patent Office: 530 Days
• Field of Search: 381/71, 381/73.1, 381/94, 381/92, 381/96
• US Class Current: 381/71.8
• CPC Class Codes: G10K 11/17817 between the output signals and the error signals, i.e. secondary path
• CPC Class Codes: G10K 11/17819 between the output signals and the reference signals, e.g. to prevent howling
• CPC Class Codes: G10K 11/17823 Reference signals, e.g. ambient acoustic environment
• CPC Class Codes: G10K 11/17825 Error signals
• CPC Class Codes: G10K 11/17854 the filter being an adaptive filter
• CPC Class Codes: G10K 11/17881 the reference signal being an acoustic signal, e.g. recorded with a microphone
• CPC Class Codes: G10K 2210/3031 Hardware, e.g. architecture
• CPC Class Codes: G10K 2210/3045 Multiple acoustic inputs, single acoustic output
• CPC Class Codes: G10K 2210/3049 Random noise used, e.g. in model identification
• CPC Class Codes: G10K 2210/3213 Automatic gain control [AGC]
• CPC Class Codes: H03H 2021/0089 System identification, i.e. modeling

Abstract

An active acoustic attenuation system is provided that increases dynamic range by adjusting the amplitude of the input signal and the error signal at respective model and error inputs (42, 44) and providing automatic self-calibration. Input and error transducers (10, 16) provide analog input and error signals which are converted by an analog to digital converter (164, 170) to digital input and error signals for input to the model (40). Digital to analog converters (176) have digital inputs from respective digital input and error signals and operate in an analog to analog mode with analog inputs from respective input and error transducers (10, 16) and analog outputs to the analog to digital converter (164, 170). Dynamic range is also increased by adjusting the amplitude of the correction signal to the output transducer (14).

Claims

1. In an acoustic system having an input for receiving an input acoustic wave and an output for radiating an out put acoustic wave, an active attenuation method for attenuating undesirable said output acoustic wave by introducing a cancelling acoutic wave from an output transducer, comprising:

sensing said input acoustic wave with an input transducer and providing an input signal;

sensing the combined said output acoustic wave and said cancelling acoustic wave from said output transducer with an error transducer and providing an error signal;

modeling said acoustic system with an adaptive filter model having a model input trom said input transducer and an error input from said error transducer and outputting a correction signal to said outpt transducer to introduce the cancelling acoustic wave such that said error signal approaches a given value;

increasing the dynamic range of said modeling by adjusting the amplitude of said input signal at said model input;

providing amplifier means at said model input for amplifying said input signal, providing means responsive to the amplitude of said input signal and controlling amplification by said amplifier means to calibrate said input signal;

providing an analog said input signal from said input transducer;

converting said analog input signal to a digital input signal with an analog to digital converter for input to said model;

providing a digital to analog converter having a digital input from said digital input a signal;

operating said digital to analog converter in an analog to analog mode with an analog input from said input transducer and with an analog output to said analog to digital converter.

2. The invention according to claim 1 comprising providing a second digital to analog converter and operating said second digital to analog converter in an analog to analog mode with an analog input from said correction signal and an analog output to said output transducer.

3. In an acoustic system having an input for receiving an input acoustic wave and an output for radiating an output acoustic wave, active attenuation apparatus for attenuating undesirable said output acoustic wave by introducing a cancelling acoustic wave from an output transducer, comprising:

an input transducer sensing said input acoustic wave and providing an input signal;

an error transducer sensing the combined said output acoustic wave and said cancelling acoustic wave from said output transducer and providing an error signal;

an adaptive filter model adaptively modeling said acoustic system on-line and having a model input from said input transducer and an error input from said error transducer and outputting a correction signal to said output transducer to introduce the cancelling acoustic wave such that said error signal approaches a given value;

means for increasing the dynamic range of said system comprising calibration means for adjusting the amplitude of said correction signal;

wherein said calibration means comprises digital to analog converter means operated in an analog to analog mode having an analog input from said correction signal and an analog output to said output transducer.

4. The invention according to claim 3 wherein said digital to analog converter means comprises:

a digital to analog converter having a voltage reference terminal receiving said correction signal, a feedback reference terminal, and first and second analog output terminals;

operational amplifier means having a pair of comparing inputs connected to respective said first and second analog output terminals, said operational amplifier means having an analog voltage output terminal connected to said feedback reference terminal and providing an analog output voltage to said output transducer.

5. In an acoustic system having an input for receiving an input acoustic ware and an output for radiating anoutput acoustic wave, an active attenuation method for attenuating undesirable said output acoustic wave by introducing a cancelling acoustic wave from an output transducer, comprising:

sensing said input acoustic wave with an input transducer and providing an input signal;

7. The invention according to claim 5 comprising providing first and second amplifier means at respective said model input and said error input for amplifying respective said input and error signals, providing first and second means responsive to the amplitude of respective said input and error signals and controlling amplification by respective said first and second amplifier means to calibrate said input and error signals.

9. The invention according to claim 7 comprising:

adaptively compensating for feedback to said input from said output transducer for both broad band and narrow band acoustic waves on-line without off-line pre-training, and providing both adaptive error path compensation and adaptive compensation of said output transducer on-line without off-line pre-training;

modeling the feedback path from said output transducer to said input transducer with the same said model by modeling said feedback path as part of said model such that the latter adaptively models both said acoustic system and said feedback path, without separate modeling of said acoustic system and said feedback path, and without a separate model pre-trained off-line solely to said feedback path;

providing an auxiliary noise source and introducing noise therefrom into said model, such that said error transducer also senses the auxiliary noise from said auxiliary noise source;

modeling both said error path and said output transducer on-line with a said adaptive filter model, and providing a copy of said second adaptive filter model in said first mentioned adaptive filter model to compensate for said output transducer and said error path.

11. The invention according to claim 9 comprising providing a third digital to analog converter and operating said third digital to analog converter in an analog to analog mode with an analog input from said correction signal and an analog output to said output transducer.

6. sensing the combined said output acoustic wave and said cancelling acoustic wave from said output transducer with an error transducer and providing an error signal;

modeling said acoustic system with an adaptive filter model having a model input from said input transducer and an error input from said error transducer and outputting a correction signal to said output transducer to introduce the cancelling acoustic wave such that said error signal approaches a given value;

increasing the dynamic range of said modeling by adjusting the amplitude of said input signal at said model input;

also increasing said dynamic range of said modeling by adjusting the amplitude of said error signal at said error input to said model.

8. The invention according to claim 6 comprising:

providing analog said input and error signals from said input and error transducers;

converting said analog input and error signals to digital input and error signals from analog to digital converter means for input to said model;

providing first and second digital to analog converters havng digital inputs from respective said digital input and error signals;

operating said first and second digital to analog converters in analog to analog modes with analog inputs from respective input and error transducers and with analog outputs to said analog to digital converter means.

10. The invention according to claim 8 comprising:

introducing noise from said auxiliary noise source which is random and uncorrelated to said input acoustic wave;

providing said second adaptive filter model having a model input from said auxiliary noise source.

12. In an acoustic system having an input for receiving an input acoustic wave and an output for ratiating an output acoustic wave, an active attenuation method for attenuating undesirable said output acoustic wave by introducing a cancelling acoustic wave from an output transducer, comprising:

sensing said input acoustic wave with an input transducer and providing an input signal;

sensing the combined said output acoustic wave and said cancelling acoustic save from said output transducer with an error transducer and providing an error signal;

modeling said acoustic system with an adaptive filter model having a model input from said input transducer and an error input from said error transducer and outputting a correction signal to said output transducer to introduce the cancelling acoustic wave such that said error signal approaches a given value;

increasing the dynamic range of said system by adjusting the amplitude of said correction signal;

providing a digital to analog converter and operating it in an analog to analog mode with an analog input from said correction signal and an analog output to said output transducer.

14. The invention according to claim 12 wherein said input transducer provides an analog said input signal, and comprising:

analog to digital converter means for converting said analog input signal to a digital input signal for input to said model;

digital to analog converter means having a digital input from said digital input signal, and having an analog input from said input transducer and having an analog output to said analog to digital converter means.

16. The invention according to claim 14 comprising a first diode connected between said comparing inputs of said operational amplifier means, and a second diode connected between said comparing inputs of said operational amplifier means in opposite polarity relation to said first diode.

18. The invention according to claim 16 wherein:

said second adaptive filter model has a model input from said auxiliary noise source, and comprising summer means summing the outputs of said error path and said second adaptive filter model and outputting the result as an error input to said second adaptive filter model;

said second adaptive filter model comprises algorithm means, and comprising multiplier means multiplying the output of said summer means with said auxiliary noise from said auxiliary noise source and applying the result as a weight update signal to said algorithm means, and comprising second summer means summing auxiliary noise from said auxiliary noise source with the output of said first adaptive filter model and supplying the result as said correction signal to said output transducer;

said first adaptive filter model comprises first and second algorithm means each having an error input from said error transducer, and comprising third summer means summing the outputs of said first and second algorithm means of said first adaptive filter model and using the result as an input to said second summer means for summing with said auxiliary noise, and comprising a first copy of said second adaptive filter model of said error path and said output transducer in said first algorithm means of said first adaptive filter model, and comprising a second copy of said second adaptive filter model of said error path and said output transducer in said second algorithm means of said first adaptive filter model;

said first algorithm means of said first adaptive filter model has an input from said input transducer, said first copy of said second adaptive filter model has an input from said input transducer, and comprising first multiplier means multiplying the output of said first copy with said error signal and using the result as a weight update signal to said first algorithm means of said first adaptive filter model;

said second algorithm means of sid first adaptive filter model has an input from said correction signal, said second copy of said second adaptive filter model has an input from said correction signal, and comprising second multiplier means multiplying the output of said second copy with said error signal and using the result as a weight update signal to said second algorithm means of said first adaptive filter model.

20. The invention according to claim 18 wherein said error transducer provides an analog said error signal, and said analog to digital converter means converts said analog error signal to a digital error signal for input to said first adaptive filter model,

and comprising second digital to analog converter means having a digital input from said digital error signal and having an analog input from said error transducer and having an analog output to said second analog to digital converter means.

22. The invention according to claim 20 wherein said third digital to analog converter means comprises:

a digital to analog converter having a voltage reference terminal receiving said correction signal, a feedback reference terminal, and first and second analog output terminals;

operational amplifier means having a pair of comparing inputs connected to respective last mentioned said first and second analog output terminals, said operational amplifier means having an analog voltage output terminal connected to said last mentioned feedback reference terminal and providing an analog output voltage to said output transducer.

13. In an acoustic system having an input for receiving an input acoustic wave and an output for radiating an output acoustic wave, active attenuation apparatus for attenuating undesirable said output acoustic wave by introducing a cancelling acoustic wave from an output transducer, comprising:

an input transducer sensing said input acoustic wave and providing an input signal;

an error transducer sensing the combined said output acoustic wave and said cancelling acoustic wave from said output transducer and providing an error signal;

an adaptive filter model adaptively modeling said acoustic system on-line and having a model input from said input transducer and an error input from said error transducer and outputting a correction signal to said output transducer to introduce the cancelling acoustic wave such that said error signal approaches a given value;

means for increasing the dynamic range of said model comprising means for sensing the amplitude of said input signal and calibration means responsive thereto for adjusting the amplitude of said input signal.

15. The invention according to claim 13 wherein said digital to analog converter means comprises:

a digital to analog converter having a feedback reference terminal providing an analog voltage input from said input transducer, a voltage reference terminal, first and second analog output terminals, and a plurality of digital input terminals;

operational amplifier means having a pair of comparing inputs connected to respective said first and second analog output terminals, said operational amplifier means having an analog voltage output terminal connected to said voltage reference terminal of said digital to analog converter and providing said analog output voltage to said analog to digital converter means.

17. The invention according to claim 13 comprising means for adaptively compensating for feedback to said input transducer from said output transducer for both broad band and narrow band acoustic waves on-line without off-line pre-training and for providing both adaptive error path compensation and adaptive compensation of said output transducer on-line without off line pre-training, and comprising:

an auxiliary noise source introducing auxiliary noise into said adaptive filter model which is random and uncorrelated with said input acoustic wave;

a second adaptive filter model adaptively modeling both said error path and said output transducer on-line without dedicated off-line pre-training; and

a copy of said second adaptive filter model in said first adaptive filter model to compensate for both said error path and said output transducer adaptively on-line.

19. The invention according to claim 17 comprising means for increasing the dynamic range of said first adaptive filter model by adjusting the amplitude of said error signal at said error input to said first adaptive filter model.

21. The invention according to claim 19 comprising third digital to analog converter means operated in an analog to analog mode having an analog input from said correction signal and an analog output to said output transducer.