Dynamic carrier system for parametric arrays

• US 20030091203A1
• Filed: 08/30/2002
• Published: 05/15/2003
• Est. Priority Date: 08/31/2001
• Status: Abandoned Application

• Current Assignee: American Technology Incorporated (Emerson Electric Company)
• Original Assignee: American Technology Incorporated (Emerson Electric Company)
• Inventors: Croft, James J. III, Spencer, Michael E.
• Application Number:
  US10/232,755
• Publication Number:
  US 20030091203A1
• Time in Patent Office: Days
• US Class Current: 381/111
• CPC Class Codes: G10K 15/02 Synthesis of acoustic waves synthesis of speech G10L13/00
• CPC Class Codes: H04R 2217/03 Parametric transducers where sound is generated or captured by the acoustic demodulation of amplitude modulated ultrasonic waves

Abstract

A system configured to dynamically adjust the ultrasonic carrier level in a parametric array system in response to changing source signal input levels, and which employs a look-ahead delay strategy to enable optimal modulation of the carrier wave to eliminate constant ultrasonic carrier emission and reduce the ultrasonic carrier emission to what is actually needed to accommodate the db range of the source material, and at the same time, to also minimize noticeable distortion and sound artifacts of a high-power ultrasonic carrier, and/or distortion/artifacts arising from modulation of an ultrasonic carrier to reduce average power output; and thus it realizes advantages of carrier modulation based on source-signal level, while minimizing inherent drawbacks of carrier modulation.

Claims

1. A method for improving performance of a parametric speaker system, comprising the steps of:

a) delaying an audio signal prior to parametrically reproducing the audio signal;

b) monitoring a level of the audio signal during the delay; and

c) modulating a carrier envelope based on the monitored level of the audio signal to provide sufficient power to produce a desired audio output and reduce carrier energy when it is not required to reproduce the signal, combining the delayed audio signal with the modulated carrier to parametrically reproduce the audio signal, thereby improving power use efficiency.

2. A method in accordance with claim 1, comprising the further step of pre-processing the audio signal to minimize distortion of the parametrically reproduced audio signal.

3. A method in accordance with claim 1, comprising the further steps of:

a) reducing sound artifacts induced by carrier modulation so as to be substantially unnoticeable to a listener by;

i) limiting a growth rate of the carrier envelope based on a first target value of the audio signal; and

ii) limiting a rate of decay of the carrier envelope based on a second target value of the audio signal.

4. A method in accordance with claim 3, comprising the further steps of:

a) providing a delay of about one millisecond; and

b) limiting the growth rate of the carrier envelope to about 70% of the first target value over the time period of the delay.

5. A method in accordance with claim 3, wherein the first target value is a peak amplitude value of the audio signal and the second target value is a minimum amplitude value of the audio signal.

6. A method in accordance with claim 1, where in the delay is up to 3 milliseconds.

7. A method in accordance with claim 1, comprising the further step of limiting the growth rate and rate of decay of the carrier envelope by limiting a change in slope of the carrier envelope as a function of time.

8. A method in accordance with claim 1, comprising the further step of analyzing the delayed audio signal and modifying the carrier envelope to comprise a smoothed envelope which encompasses the audio signal.

9. A method in accordance with claim 8, comprising the further step of modulating the smoothed carrier signal envelope so that the rate of increase and the rate of decay of the carrier envelope are both controlled to be within a preset limit.

10. A method in accordance with claim 9, comprising the further step of imposing the audio signal on the smoothed modulated carrier envelope to produce a sideband signal, thereby minimizing distortion of the sideband signal due to carrier envelope modulation.

11. A method in accordance with claim 1, comprising the further step of pre-distorting the audio signal to substantially compensate for undesirable distortion introduced by modulation of the ultrasonic envelope.

12. A method in accordance with claim 1, comprising the further step of pre-distorting the carrier envelope to compensate for distortion induced by modulation of the carrier envelope.

13. A method in accordance with claim 1, comprising the further step of sampling the level of the audio signal during the time delay and calculating an optimal modification to the modulation of the carrier envelope based on the audio signal to reduce undesirable audio artifacts of carrier envelope modulation.

14. A method for improving performance of a parametric speaker system, comprising the steps of:

a) delaying an audio signal prior to parametrically reproducing the audio signal;

b) monitoring a level of the audio signal during the delay; and

c) modulating a carrier envelope to be associated with the audio signal so as to limit growth and decay ahead of and behind rapid changes in the audio signal level to smooth the carrier envelope to reduce audio artifacts resulting from comer modulations, whereby power use efficiency of parametric reproduction is increased and noticeable distortion of the audio signal is reduced.

15. A system for optimizing carrier signal strength for dynamic audio signal reproduction in a parametric audio reproduction system, comprising:

a) a time delay processor for delaying an audio signal to enable sensing and processing of the audio signal prior to parametrically reproducing the audio signal;

b) a signal envelope sensor configured to sense an envelope corresponding to a parameter of the audio signal; and

c) a carrier wave generator configured to generate a modulated carrier wave based on the envelope sensed by the signal envelope sensor;

d) wherein the audio signal is delayed, the signal envelope is sensed, and the carrier wave is generated and modulated to improve power use efficiency in parametric reproduction of the audio signal.

16. A system in accordance with claim 15, further comprising a pre-processor configured to pre-process the audio signal to create minimal detectable distortion of the audio signal.

17. A system in accordance with claim 15, wherein the carrier wave generator modulates the carrier wave by increasing or decreasing a growth or decay rate of the carrier wave based on a target value of the audio signal.

18. A system in accordance with claim 15, further comprising a pre-processor configured to pre-process the audio signal to create minimal detectable distortion of the audio signal.

19. A system in accordance with claim 15, wherein the time delay processor delays the audio signal by up to 3 milliseconds.

20. A system in accordance with claim 15, wherein the carrier wave generator modulates the carrier wave such that a rate of increase and a rate of decay of the carrier wave are both controlled to be within a preset limit.

21. A system in accordance with claim 15, further comprising an audio signal processor which pre-distorts the audio signal to substantially compensate for undesirable distortion induced by modulation of the carrier wave.

22. A system in accordance with claim 15, further comprising a carrier wave processor which pre-distorts the carrier wave to substantially compensate for undesirable distortion induced by modulation of the carrier wave.