For a prop I'm building, I'd like to include a little easter egg which will play back one or two short audio samples via the included DAC.
Now, the circuit doesn't contain any additional flash ram for storing the samples, so I need to fit them into the built in flash or progmem. I don't know exactly how much progmem I have left, but let's just assume it's less than 4K and I've got 1K of flash. That isn't much for one audio sample let alone two, so I've been looking for a simple way to compress and decompress the audio. If I could get even a 2:1 compression ratio, that would be fantastic.
I know about delta coding, but delta coding isn't a compression algorithm, it just converts the audio into a form which is easier to compress. So I've been trying to finding the best method by which to compress the delta coded audio sample, which I can then deompress in realtime on playback, but so far I haven't had much luck.
At this point I'm looking at the wikipedia article on entropy encoding... I think I want to use one of these schemes, but I'm not sure which one is best suited for audio. One which does not require a table of symbols would probably be best.