Method and apparatus for envelope detection and enhancement of pitch cue of audio signals

Abstract

A method and apparatus for detecting an envelope of an audio signal, and a method and apparatus for enhancing the pitch cue of an audio signal perceived by a cochlear implant patient where the audio signal is processed and input to an implant device of the recipient. The methods and apparatuses use techniques such as filtering, rectifying, detecting peak values, sampling, resetting, comparing and multiplying various signals to detect the envelope or enhance the pitch cue of the audio signal.

Description

FIELD OF THE INVENTION [0001] The present invention relates to hearing prosthesis and to sound processing devices and methods associated with hearing prosthesis. In particular, the present invention relates to an apparatus and method of envelope detection that is simple to implement in both analog circuitry or digital signal processing and assists cochlear implant recipients to better perceive changes in the amplitude of speech than is currently the case. Furthermore, the invention relates to an apparatus and method for enhancing the pitch cue of an audio signal perceived by a cochlear implant recipient. BACKGROUND OF THE INVENTION [0002] In many people who are profoundly deaf, the reason for deafness is absence of, or destruction of, the hair cells in the cochlea which transduce acoustic signals into nerve impulses. These people are unable to derive suitable benefit from conventional hearing aid systems, no matter how loud the acoustic stimulus is made, because there is damage to o...

AI Technical Summary

Benefits of technology

[0040] The present invention through processing the filtered signal in one or more frequency ranges of interest, provides an improved method of estimating the amount of energy present in a frequency band used by a cochlear implant.

[0045] This is in contrast with the prior art which aims to produce a smooth envelope signal which varies slowly compared to the centre frequency of the filter, thereby removing all of the fin timing structure of the filtered signal.

[0061] Thus at high frequencies, preferably more than four times the audio frequency, the method conveys fine timing content of the filter output signal giving an enhanced pitch cue to the implant recipient. Whilst at lower frequencies, preferably less than twice the audio frequency, the method implements envelope detection.

Problems solved by technology

These people are unable to derive suitable benefit from conventional hearing aid systems, no matter how loud the acoustic stimulus is made, because there is damage to or absence of the mechanism for nerve impulses to be generated from sound in the normal manner.

As the ability to perceive sound is of fundamental importance to cochlear implant recipients, the ability to reproduce sound and the percepts of speech via electrical stimulation using a cochlear prosthesis is one of the major challenges of this technology.

These strategies utilise envelope detection for processing the output of a series of filters, however a disadvantage of such systems is that the output of the envelope detector typically includes a large amount of ripple and / or the desired envelope becomes excessively smeared out.

This has the disadvantage of adversely affecting the temporal cues that are important in consonant perception.

Another prior system called quadrature envelope detection, although producing an envelope which substantially contains no ripple and is not smeared out, has the disadvantage that it is complex and requires twice as many band pass filters as there are frequency channels which results in additional cost and complexity.

Furthermore, the need to provide the function of squaring and square root operations is generally not practical in analogue circuitry.

At high stimulation rates, the fine timing content generally has not been taken into account and therefore implant recipients have not been able to adequately perceive pitch in an audio signal.

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