This directory contains version 1.2 of a simple 16 bit PCM <-> 4 bitADPCM coder and decoder. See the source and the manpage for commentson the algorithm.If you have previously used version 1.0: there was a bug in it. Thisversion fixes the bug. (1.1 fixed that, but had another slight bugthat caused loss of quality on SGI machines).The routines have been tested on an SGI Indigo running Irix 4.0.2 and4.0.5F and on a Sun Sparc SLC running SunOS 4.1.1. There are no realmachine dependencies, though, so there should be no problems on otherarchitectures. There is a timing program to test how fast the stuff runs on yourmachine. Here are some sample numbers:R4000 Indigo:	compress: 1.1Msample/sec, decompress: 1.7Msample/secR3000 Indigo:	compress: 410Ksample/sec, decompress: 850Ksample/secSun SLC:	compress: 250Ksample/sec, decompress: 420Ksample/secMac-IIsi	compress   21Ksample/sec, decompress:  35Ksample/secI'd be interested in numbers for PC class machines.Also included are some simple test programs that convert audio filesto/from 4bit ADPCM samples. Rawcaudio/rawdaudio convert to/from raw16bit PCM files; sgicaudio/sgidaudio convert to/from SGI AIFF filesand suncaudio/sundaudio convert to/from SUN/NeXT format audio files.The Sun program was donated by Hughes Doug, hughes@sde.mdso.vf.ge.com(it is actually only one program and looks at the program name todecide whether to compress or decompress). Oh yeah, the sun and sgicompressors will probably only compile on those machines. Also, forthe sgi compressor you need the Digital Media Developers Option, which(I think) is available with Irix 4.0.5.Note: I have had to make a few changes to the sun audio converter, butunfortunately I have no way of testing the result (since it needsSolaris 1.somethingorother which I don't have). If the program doesnot work and someone fixes it I would like to get a copy.Finally, there is a uuencoded adpcm sound file of me saying "helloworld" (with a cold) that you can use to test that everything workscorrectly.  (rawdaudio <hello.adpcm >hello.pcm)If you use this package I would like to hear from you.I am especially interested in people who can test interoperabilitywith proven Intel/DVI ADPCM coders. I have tried to get the algorithmcorrect, but you never know....Answers to often-asked questions:- No, this is *not* a G.721 coder/decoder. The algorithm used by G.721  is very complicated, requiring oodles of floating-point ops per  sample (resulting in very poor performance). I have not done any  tests myself but various people have assured my that 721 quality is  actually lower than DVI quality.- No, it is not a CDROM-XA coder either, as far as I know. I haven't  come across a good description of XA yet.- No, testc and testd are not full-blown audio-file converters, only  simple test programs. If you write a file-converter (like caudio.c,  which compresses Sun audio files) and you're willing to donate it  I'd be very happy to include it in the distribution.- Also, I know next-to-nothing about who IMA are. Their address, though,  from their May 1992 proceedings (where I got the algorithm from):	IMA Compatability Project Headquarters	9 Randall Court	Annapolis MD 21401	USA	Phone: (410) 626-1380	Fax:   (410) 263-0590They might be able to send back issues of their proceedings, I don'tknow.	Jack Jansen	Centre for Mathematics and Computer Science	Kruislaan 413	Amsterdam	the Netherlands	+31 20 592 4098	Jack.Jansen@cwi.nl