Efika 5200B Project Reggae on Efika in category Multimedia proposed by Grzegorz Kraszewski on 21st February 2006 (accepted on 20th March 2006) [View Full Project]

Blog Entry

	IMA ADPCM - a hard nut to crack? posted by Grzegorz Kraszewski on 4th December 2006 I've been asked lately to implement WAVE IMA ADPCM decoder in Reggae. As I like to implement new decoders, I've started work on it. The algorithm seems to be well documented (the source is probably original MicroSoft document, of course I have read it), so I have been a bit surprised, when my decoder produced hearable distortions at block boundaries. I've played the same file with WinAMP, there were no distortions, so it is my fault obviously. I've compared my decoder with libsndfile implementation, but haven't found the bug yet. Now I'm analysing the algorithm step by step, either I've made some bug (documentation misinterpretation?), or the documentation is not precise. I hope I will solve the problem this week. Then I can optimize the decoder, the plan is to replace lookup step table with polynomial approximation, as lookup tables kill AltiVec performance (and fast scalar CPU performance, as PowerPC is, as well).