Re: Lowest CPU utilization audio codec?

On Thu, 22 Jan 2004, Jim Leonard wrote:

> I thought IMA ADPCM would be the best approach, but it would only halve
> the size of the data (4-bit ADPCM vs. 8-bit PCM) and I was hoping to get

	There is really no reason that ADPCM has to be transmitted as a
series of 4-bit samples. I have seen (or at least heard about) 5-bit,
3-bit, and I think 2-bit ADPCM variants, of the IMA algorithm, no less.

> a bit more compression...  I also recall John Ratcliffe's "adaptive
> ADPCM" that achieved between 3:1 to 6:1 for speech and was essentially
> ADPCM with multiple tables, but I've lost my Dr. Dobb's article on that
> from a decade ago.

	"adaptive ADPCM" = "adaptive adaptive differential PCM"?...:)
Anyway, the 3:1 and 6:1 thing...sounds like it could be MACE compression--
Macintosh Audio Compression and Expansion. It came in 3:1 and 6:1 flavors,
which were denoted by fourccs 'MAC3' and 'MAC6', respectively. ffmpeg/lavc
has code to decode both, but not compress it. I'm not sure about quality
as I have never worked much with it.

--
	-Mike Melanson


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