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From: riley@batcomputer.tn.cornell.edu (Daniel S. Riley)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Fibonacci Compression???
Message-ID: <10069@batcomputer.tn.cornell.edu>
Date: 8 Apr 90 15:15:49 GMT
References: <9004071643.AA01559@jade.berkeley.edu>
Reply-To: riley@tcgould.tn.cornell.edu (Daniel S. Riley)
Organization: Cornell Theory Center, Cornell University, Ithaca NY
Lines: 29

In article <9004071643.AA01559@jade.berkeley.edu> C503719@UMCVMB.BITNET ("Baird McIntosh") writes:
>Ok... from Perfect Sound 3.0 manual:
>"COMP saves the file in IFF format using Fibonacci Delta Compression, a
> technique that stores each sample as a four bit offset from the previous
> sample.  This will cut your file size in half, but may reduce the sound
> quality considerably."
>
>For any more technical information, like what value each bit of the 4-bit
>offset represents, you'll need to refer to the amiga.tech gurus...

Fibonacci delta compression uses the first few numbers of the Fibonacci
series (x(n) = x(n-1) + x(n-2), x(0) = x(1) = 1) as deltas.  The actual
nubmers used are

BYTE codeToDelta[16] = {-34,-21,-13,-8,-5,-3,-2,-1,0,1,2,3,5,8,13,21};

The individual bits don't represent anything--you just take 4 bits,
look that number up in the table, and that's your offset.

This represents small changes fairly accurately, but is miserable
representing large changes, so there is potential for a lot of 
distortion.  In practice, it's ok for sound effects and such, but
questionable for anything that will be listened to critically.

This is, btw, all documented in the IFF specs, available on disk
from CATS and on paper in the RKMs.

-Dan Riley (riley@tcgould.tn.cornell.edu, cornell!batcomputer!riley)
-Wilson Lab, Cornell University