Pitch perception in an auditory prosthesis

• US 20060080087A1
• Filed: 09/28/2005
• Published: 04/13/2006
• Est. Priority Date: 09/28/2004
• Status: Active Grant

• Current Assignee: Hearworks Pty., Ltd. (Cochlear Limited)
• Original Assignee: Hearworks Pty., Ltd. (Cochlear Limited)
• Inventors: Seligman, Peter, Vandali, Andrew, Van Hoesel, Richard
• Granted Patent: US 8,023,673 B2
• Time in Patent Office: Days
• US Class Current: 704/207
• CPC Class Codes: A61N 1/36038 Cochlear stimulation
• CPC Class Codes: G10L 2021/065 Aids for the handicapped in understanding
• CPC Class Codes: G10L 21/0364 for improving intelligibility
• CPC Class Codes: G10L 25/18 the extracted parameters being spectral information of each sub-band
• CPC Class Codes: H04R 25/505 using digital signal processing
• CPC Class Codes: H04R 25/606 acting directly on the eardrum, the ossicles or the skull, e.g. mastoid, tooth, maxillary or mandibular bone, or mechanically stimulating the cochlea, e.g. at the oval window

Abstract

A sound processing process, device and software are disclosed which seek to improve pitch perception, with particular application to auditory prostheses. After input sound signals are processed into channels, an algorithm is applied to selectively increase the modulation depth of the envelope signals. In certain embodiments, the channelized signals are adjusted in timing so as to align the phase of modulated envelope signals in different channels. This results in provision of synchronous (phase aligned) modulation periodicity across channels and hence less pitch ambiguity for listeners to the processed signal, or for application of the signal to hearing prostheses such as cochlear implants. In some embodiments, a broadband envelope signal is used to modulate the level of the narrow band channel signals, so that voicing frequency modulation information in the broadband envelope signal is provided in all narrow band channel signals and the phase of modulated signals in the channels are aligned. A preferred form uses an envelope signal which is modified to increase its modulation depth, and is normalized so as to allow for modulation of the channel signals.

Claims

1. A method for processing a sound signal having a fundamental frequency, the method comprising:

processing the sound signal to produce channel signals in spaced frequency channels;

determining an envelope signal for each of a plurality of the channel signals; and

modulating the envelope signals in each channel with at least one broadband envelope signal derived from the input sound signal, such that the phase of modulated signals in the narrow band channels are synchronized.

2. The method of claim 1, wherein the at least one broadband envelope signal contains modulation information related to the fundamental frequency of the sound signal, and wherein the modulated envelope signals contain the modulation information.

3. The method of claim 1, wherein the broadband envelope signal has a modulation depth, and wherein the method further comprises:

increasing the modulation depth of the broadband envelope signal prior to modulating the envelope signals.

4. The method of claim 3, wherein increasing the modulation depth of the broadband envelope comprises:

increasing the modulation depth of the broadband envelope signal such that the average modulation depth in each channel is increased.

5. The method of claim 1, further comprising:

performing additional sound processing operations on the modulated envelope signals and any remaining channel signals.

6. The method of claim 1, further comprising:

modifying the channel signals to substantially remove amplitude modulation in the channel signals, prior to modulating the envelope signals with a broadband envelope signal.

7. The method of claim 1, further comprising:

normalizing the broadband envelope signal prior to modulating the envelope signals with a broadband envelope signal.

8. The method of claim 3, wherein increasing the modulation depth of the broadband envelope signal comprises:

transforming the broadband envelope signal with a function so as to increase the modulation depth of periodic terms in the broadband envelope signal.

9. The method of claim 1, wherein modulating the envelope signals with at least one broadband envelope signal comprises

modulating the envelope signals with a plurality of broadband envelope signals derived from the received sound signal, each broadband envelope signal corresponding to different frequency regions of the received sound signal, and wherein each broadband envelope signal is used to modulate the level of channel signals derived within its respective frequency region.

10. A machine readable medium storing instructions that, if executed by a computer system, causes the computer system to perform a set of operations to process a sound signal having a fundamental frequency, comprising:

processing the sound signal to produce channel signals in spaced frequency channels;

determining an envelope signal for each of a plurality of the channel signals; and

modulating the envelope signals with at least one broadband envelope signal containing modulation information related to the fundamental frequency of the sound signal such that the modulated envelope signals have synchronized phases and contain the modulation information related to the fundamental frequency of the sound signal.

11. The method of claim 10, where the received sound signal is a voiced signal, and further wherein the fundamental frequency of the input sound signal is a voicing frequency.

12. The method of claim 10, wherein the broadband envelope signal has a modulation depth, and wherein the method further comprises:

increasing the modulation depth of the broadband envelope signal prior to modulating the envelope signals.

13. The method of claim 10, further comprising:

modifying the channel signals to substantially remove amplitude modulation in the channel signals, prior to modulating the envelope signals with a broadband envelope signal.

14. The method of claim 10, wherein modulating the envelope signals with at least one broadband envelope signal comprises

modulating the envelope signals with a plurality of broadband envelope signals derived from the received sound signal, each broadband envelope signal corresponding to different frequency regions of the received sound signal, and wherein each broadband envelope signal is used to modulate the level of channel signals derived within its respective frequency region.

15. A speech processing unit for processing a sound signal, comprising:

a filter bank configured to process the sound signal to generate envelope signals in each of a plurality of spaced frequency channels;

a broadband envelope detector configured to measure the envelope of at least one broadband signal; and

a channel modulation module that uses the at least one broadband envelope signal to modulate the channel envelope signals to generate modulated envelope signals.

16. The speech processing unit of claim 15, wherein the filter bank comprises:

a plurality of band-pass filters each configured to channel the sound signal into one of the plurality of spaced frequency channels; and

a plurality of envelope detectors each corresponding to one of the plurality of band-pass filters and configured to estimate the envelope signal of the sound signal in each spaced frequency channel.

17. The speech processing unit of claim 16, wherein the plurality of band-pass filters comprise:

narrow bandwidth band-pass filters for low-frequency channels and wider bandwidth band-pass filters for higher frequency channels.

18. The speech processing unit of claim 15, wherein the filter bank provides an estimate of the envelope signals in each channel at regular time intervals.

19. The speech processing unit of claim 15, wherein the channel modulation module comprises:

a plurality of low-pass filters each configured to low-pass filter a corresponding envelope signal to remove any amplitude modulation corresponding to fundamental frequencies in voiced speech signals; and

a multiplier configured to multiply the low-pass filtered signals generated by the plurality of low-pass filters by the broadband envelope signal generated by the broadband envelope detector.

20. The speech processing unit of claim 15, wherein the broadband envelope detector comprises:

a full-wave rectifier that full-wave rectifies the sound signal;

a low-pass filter that receives the full-wave rectifies the sound signal and generates a low-pass filter envelope signal;

a high-pass filter that removes the direct current component from the low-pass envelope signal;

an adder configured to add a scaled version of the low-pass filter envelope signal to the signal generated by the high-pass filter;

a half-wave rectifier that half-wave rectifies the signal generated by the adder to remove negative excursions in the signal;

a multiplier configured to multiple the scaling factor an the low-pass filtered signal; and

a normalizer that scales the amplitude of the signal generated by the half-wave rectifier such that its peak level over a finite time interval is set to unity, to generate the broadband envelope signal.

21. The speech processing unit of claim 20, wherein the low-pass filter is configured to apply a 300 Hz, 6^th order Butterworth, infinite impulse response (IIR) to generate the LPF envelope.

22. The speech processing unit of claim 20, wherein the high-pass filter is an 80 Hz, 2^nd order Butterworth, IIR high-pass filter.

23. The speech processing unit of claim 20, wherein the low-pass filter is a 50 Hz, 2^nd order Butterworth, IIR LPF.

24. The speech processing unit of claim 20, further comprising:

a maxima selection module configured to select a subset of the channels on which modified envelope signals having the largest amplitude at a given instance in time occur; and

an encoder configured to use the selected channels to generate electrical stimuli corresponding in stimulus intensity and electrode number to the amplitude and frequency of the selected channels.

25. An auditory prosthesis for generating a therapeutic output representative of a received sound signal, comprising:

a speech processing unit configured to process the sound signal to produce channel signals in spaced frequency channels;

to determine an envelope signal for each of a plurality of the channel signals; and

to modulate the envelope signals with at least one broadband envelope signal containing modulation information related to the fundamental frequency of the sound signal such that the modulated envelope signals have synchronized phases and contain the modulation information related to the fundamental frequency of the sound signal.

26. The auditory prosthesis of claim 25, wherein the speech processor comprises:

a filter bank configured to process the sound signal to generate envelope signals in each of a plurality of spaced frequency channels;

a broadband envelope detector configured to measure the envelope of at least one broadband signal; and

a channel modulation module that uses the at least one broadband envelope signal to modulate the channel envelope signals to generate modulated envelope signals.

27. The auditory prosthesis of claim 25, wherein the auditory prosthesis comprises a cochlear implant system.

28. A speech processing unit for processing a sound signal, comprising:

means for processing the sound signal to produce channel signals in spaced frequency channels;

means for determining an envelope signal for each of a plurality of the channel signals; and

means for modulating the envelope signals with at least one broadband envelope signal containing modulation information related to the fundamental frequency of the sound signal such that the modulated envelope signals have synchronized phases and contain the modulation information.

29. The speech processing unit of claim 28, where the received sound signal is a voiced signal, and further wherein the fundamental frequency of the input sound signal is a voicing frequency.

30. The speech processing unit of claim 28, wherein the broadband envelope signal has a modulation depth, and wherein the method further comprises:

means for increasing the modulation depth of the broadband envelope signal prior to modulating the envelope signals.