Entrainment resistant feedback cancellation

Abstract

This invention concerns a method, and a device, for feedback cancellation. This invention also concerns a computer program product comprising computer program code means to make a computer execute a procedure for feedback cancellation. The method comprises providing an adaptive feedback cancellation filter which adapts under the control of a control module, and filtering at least one input of the control module to suppress correlated signals from the input prior to the control module operating upon the input. The device comprises an adaptive feedback cancellation filter, a control module and at least one filter. The control module controls adaptation of the adaptive feedback cancellation filter. The filter suppresses correlated signals from an input to the control module prior to the control module operating upon the input.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]The present application is a National Phase Patent Application and claims the priority of International Application Number PCT / AU2008 / 001807, filed on Dec. 8, 2008, which claims priority from Australian Provisional Patent Application No 2007906684 filed on 7 Dec. 2007, the content of which is incorporated herein by reference.TECHNICAL FIELD[0002]The present invention relates to sound processing devices in which an acoustic sound input is processed and converted to an acoustic sound output, and in particular relates to the cancellation of acoustic feedback in such a device when the sound input may include tonal and other periodic components.BACKGROUND OF THE INVENTION[0003]Typical sound processing devices, such as hearing aids, comprise a microphone or other input transducer to pick up acoustic sounds and convert them into an electrical signal, an electronic processor and / or amplifier to increase the power of the electrical signal, and a s...

AI Technical Summary

Benefits of technology

The present invention provides a method, device, and computer program product for feedback cancellation. The feedback cancellation filter adapts under the control of a control module and filters the input of the control module to suppress correlated signals. This helps to reduce the impact of auto-correlated signals on the control module's operation. The control module uses a NLMS or LMS algorithm to process the signals. The method and device can improve the signal-to-noise ratio and make the control of the system more effective. Additionally, the method and device can also involve partial notch suppression for systems where the NLMS algorithm is operating on whitened signals.

Problems solved by technology

At this equilibrium level the hearing aid device usually emits a continuous and unpleasant high pitched whistle or squeal.

Further, oscillation and instability in the processing path are undesirable because they can distort the signal processing performance.

This can lead to problems both for the hearing aid user and for those around.

However, this means that the desired high-frequency response of the instrument must be sacrificed in order to maintain stability, which is particularly undesirable given that human hearing loss often occurs to a greater extent in the higher audible frequencies than in the lower frequencies.

A further difficulty in feedback cancellation arises where an input sound signal comprises tonal and other periodic signals which ideally should not be cancelled, such as music, beeps, dial tones and the like.

Such tonal signals can be difficult for signal processing techniques to distinguish from oscillatory feedback which should be cancelled.

However, tonal signals of interest such as music also have a strong auto-correlation, with the result that feedback cancellation is inappropriately applied to the music signal in such techniques.

This can result in a decreased efficacy of cancellation of actual feedback signals occurring simultaneously with the tonal input, and / or the production of audible artefacts such as ‘warbling’ when the tonal signal of interest is present.

However, such filter training necessitates an extra step in hearing aid fitting or implementation.

Further, such fixed filters tend to have a limited range of situations in which feedback cancellation is adequately provided.

However, not all tones lead to corruption of filter taps, and such systems can thus detect a tone and reach a false positive determination that a filter has been corrupted, even when the filter has not been corrupted or has not been unacceptably corrupted.

Conversely, tonal signals which may not be detected by a tone detector can nevertheless cause filter corruption, leading to a false negative determination.

However a slowly adapting filter is susceptible to producing short bursts of feedback squeal if the feedback path changes faster than the FBC's adaptation rate.

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