Edward Chau

Complexity reduction and regularization of a fast affine projection algorithm for oversampled subband adaptive filters

The affine projection algorithm (APA) has been shown to improve the performance of oversampled subband adaptive filters (OS-SAFs) compared to classical normalized least mean square (NLMS) algorithms. Because of the complexity of APA, however, only low-order APAs are practical for real-time implementation. Thus, we propose a reduced-complexity version of the Gauss-Seidel fast APA (GSFAPA) for adapting the subband filters in OS-SAF systems. We propose modifying the GSFAPA with a complexity reduction method based on partial filter update, and also with a low-cost method for combined regularization and step size control. We show the advantage of the new algorithm - termed low-cost Gauss-Seidel fast affine projection - compared to the APA in a subband echo canceller application.

Window Based Prototype Filter Design for Highly Oversampled Filter Banks in Audio Applications

This paper describes a window based method for designing near perfect-reconstruction prototype filters for highly oversampled, complex modulated filter banks. The design method extends some well-known simple methods for critically sampled filter banks to the over-sampled case and to the case of different length analysis and synthesis filters. This design method is simple and effective for designing a large range of filter bank configurations. The design method is particularly useful in developing audio applications using oversampled filter banks where the target systems requirements are highly variable. The simplicity and flexibility of the design method means that this one method can be used to generate multiple prototype filters as the application requirements change

A subband beamformer on an ultra low-power miniature DSP platform

This paper presents the design and implementation of a subband cardioid beamformer on an ultra low-power miniature DSP platform, using a 2-microphone endfire array. The subband beamformer extends the classical time-domain, narrow-band algorithm to a frequency-domain, broadband implementation, so it is suitable for general speech and audio applications. An oversampled, weighted overlap-add filterbank is used to allow wide gain and phase adjustments for low power, low group delay requirements. A subband IIR filter is proposed to overcome the non-zero bandwidth of the frequency bands, and to introduce a nearly linear phase adjustment across the bands. The subband implementation allows the flexibility of integrating the beamformer with additional algorithms at different frequency ranges. The beamformer has been implemented in real-time on Dspfactorys Toccata platform, which has been specifically designed for ultra low-power, miniature, head-mounted audio devices. At 1.25 Volts with a 5 MIPS DSP core, the Toccata consumes only about 800 micro Watts without microphones and receivers.

Joint filterbank structures for integrating audio coding into hearing aid applications

To help develop ultra-low power wireless hearing aid products, we investigate the integration of subband audio coding with hearing aid applications. Both the audio coding and the hearing aid application use subband processing, but their requirements for the filterbanks are totally different. The hearing aid application typically uses an oversampled filterbank to reduce the aliasing in each subband, whereas the audio codec needs a critically sampled filterbank for maximal coding efficiency. A joint filterbank structure is proposed in this paper to satisfy these contradictive filterbank requirements. With this structure, the two filterbanks are combined into a single stereo filterbank operation, which can be efficiently implemented on a filterbank coprocessor. This structure substantially reduces the computation complexity, power consumption and memory usage.

Oversampled filter bank evaluation for joint subband audio processing and coding

This paper presents an experimental evaluation of oversampled, modulated filter banks for joint subband audio processing and coding applications. Joint subband processing and coding may be useful in some wireless audio devices such as advanced wireless digital hearing aids. We examine the use of oversampled GDFT and cosine modulated filter banks and propose using single sideband (SSB) real-valued filter banks as a compromise which is ideal for this application. The SSB filter bank provides real-valued signals for audio coding which are free from any aliasing cancellation constraints and hence are also suitable for audio processing such as subband gain adjustment. We support this conclusion with an experimental analysis of various filter bank designs for subband gain adjustment and subband audio coding.