FAMbac Project

FAMlet Based Audio Codec Development

Applied Research and Developments

We started by studying the properties of the FAMlet transform, which is used to produce frequency warped (a-domain) signals. The quantization effects of the a-domain signals and the reconstruction problems were analyzed.

Two basic problems were found:

- Robust and quantization-tolerant inverse FAMlet transform?

- How to control the quantization noise?

(This part was active during 6/95 - 11/95)

In this step the Fourier transform was combined with the FAMlet transform in order to produce auditory filterbanks. The quantization effects were

analyzed.

Here the main problems are:

- Robust and quantization-tolerant inverse FAMlet transform?

- How to realize critical sampling in a nonuniform resolution filterbank?

- Effective implementation of an ERB-rate filterbank?

(This part was active during 10/95 - 1/96)

The third and up to now the most succesful line has been the WLP [ICASSP 94]. Promising results achieved with monophonic WLPAC 1.0 codec are published in [AES-97]. Presently the codec implementation is going on (see part 4.). The quantization noise of this codec has been compared with that of the MPEG-type of codecs. WLPAC produces automaticly, without any explicit auditory model, very similar noise pattern as that of MPEG.

The first monophonic codec has been extented for stereophonic signals. The novelty in this codec is to use analytic signals. The left and right channels are mapped by the Hilbert transform in the negative and in the positive frequencies correspondingly. This analytic signal is then processed with complex valued WLP. Now the WLP automaticly optimizes the use of the WLP coefficients between the channels.

Interesting results of this stereophonic codec is published in [ICASSP 97].

(This part has been active since 1/96)

The WLPAC 1.0 codec will be implemented with TI TMS320C30 processor (BW: 12 kHz, 48 kbps). One processor is able to do realtime encoding and decoding. The implementation is financed by VistaCom Inc.

(This part has been active since 2/97)

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• Published papers are available here.