Bit Sliced Arithmetic Coding (BSAC)

Bit-Sliced Arithmetic Coding (BSAC) is an audio coding algorithm developed by Samsung [1] to offer fine-grain bitrate scalability. It is part of the MPEG-4 standard [2] and demonstration software can be compiled from the publicly-available MPEG-4 Reference Software (2001 Edition).

The following single-channel sound files compare coding efficiencies of BSAC and Scala codecs at two different bitrates. All files are approximately 6 seconds in length with 44.1 kHz sample rate; samples are presented both as compressed bitstreams and uncompressed (decoded) .wav files. For verification, the BSAC bitstreams can be decoded using an MPEG-4 reference software decoder, while Scala bitstreams can be decoded using the demonstration decoder software available from this site.

 

Signal	Original file (uncoded)		Mono Bitrate
			32 kbit/s		64 kbit/s
			BSAC	SCALA	BSAC	SCALA
harpsichord	harp.wav	bitstream	harp32.mp4	harp32.sab	harp64.mp4	harp64.sab
		decoded wav	harp32_bsac.wav	harp32_sac.wav	harp64_bsac.wav	harp64_sac.wav
female voice	voice.wav	bitstream	voice32.mp4	voice32.sab	voice64.mp4	voice64.sab
		decoded wav	voice32_bsac.wav	voice32_sac.wav	voice64_bsac.wav	voice64_sac.wav
castanets	cast.wav	bitstream	cast32.mp4	cast32.sab	cast64.mp4	cast64.sab
		decoded wav	cast32_bsac.wav	cast32_sac.wav	cast64_bsac.wav	cast64_sac.wav

 

For some signals such as harpsichord, BSAC performance at 64 kbit/s is similar to the Scala codec. However BSAC suffers from poor coding efficiency at lower bitrates, indicated by the 32 kbit/s samples where the Scala codec achieves significantly better coding quality for all three test signals. Error-resilient coding is a further advantage of the Scala codec.

References

[1] S. H. Park et al., "Multi-Layer Bit-Sliced Bit Rate Scalable Audio Coding," presented at the 103^rd Convention of the Audio Engineering Society, New York, paper 4520 (1997 Sep.).

[2] ISO/IEC JTC1/SC29/WG11 N2803, "MPEG-4 Audio Version 2 (Final Committee Draft 14496-3 AMD1)", Vancouver, Canada (1999 July).