Pitch perception in an auditory prosthesis
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.
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 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.
6. The method of claim 1 , further comprising:
performing additional sound processing operations on the modulated envelope signals and any remaining channel signals.
7. 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.
8. The method of claim 1 , further comprising:
normalizing the broadband envelope signal prior to modulating the envelope signals with a 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. 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.
11. The auditory prosthesis of claim 10 , 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.
12. The auditory prosthesis of claim 10 , wherein the auditory prosthesis comprises a cochlear implant system.
13. 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.
14. The speech processing unit of claim 13 , where the received sound signal is a voiced signal, and further wherein the fundamental frequency of the input sound signal is a voicing frequency.
15. The speech processing unit of claim 13 , 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.