[Flac-dev] Re: Lossless AMI ADPCM

[Juhana Sadeharju]

>From:	Josh Coalson <j_coalson at yahoo.com>
>
>I'm copying the flac-dev list to see if anyone has any
>feedback also...

I'm supposed to be there myself since yesterday but have not got
the first digest yet.

>First, the results they show are for compression of data
>that has already been lossily quantized to fewer bits per
>sample, e.g. u-Law and A-Law are logarithmic quantizations
>of 16-bit data to 8-bit.

I thought the author has two models, A-law and AMI ADPCM, which
both he extends. AMI ADPCM starts with 16-bit samples, but I'm not
sure if A-law is involved in that process.

>Second, the average ratio (assuming the table describes
>ratios, since the omitted the units) for 44.1kHz audio
>is 3:1.

I though they are bits/sample. The text says "from the table one
can see that the software works better for audio": average for audio
is 2.75, and average for audio/speech is 3.17. So, 2.75 is better
only if it is the number of bits (or such).

>They only vaguely mention the sources for the
>material.  I can choose material that gives those ratios
>even for linear PCM.

Yeah, and it is supposed to be a scientific paper. Considering
that the author has e-mail address, I would have expected him
to check against Shorten which he even references.

>expensive.  Standard autocorrelation->Levinson-Durbin
>will be too slow.  So they use RLS, which has stability
>problems.

His RLS seems to be stable enough, up to 5000 samples, and fast.
Would the RLS make FLAC run faster?

>I have done some tests with long kernels and it does
>not buy very much extra compression.  Most of the slack
>can be taken up with better entropy coding.

OK.
But if anyone understands the further details of the algorithm,
I would like to code and test it out. I have written down as much
details as I could --- they are available via e-mail for those who
didn't got the entire first mail on this topic. Perhaps it would be
a waste of time, but the author of that paper should have mentioned
the audio sources in the first place. Bad science.

Regards,

Juhana