www.pudn.com > speakfs72.zip > README, change:2002-01-05,size:3569b


This directory contains version 1.2 of a simple 16 bit PCM <-> 4 bit 
ADPCM coder and decoder. See the source and the manpage for comments 
on the algorithm. 
 
If you have previously used version 1.0: there was a bug in it. This 
version fixes the bug. (1.1 fixed that, but had another slight bug 
that caused loss of quality on SGI machines). 
 
The routines have been tested on an SGI Indigo running Irix 4.0.2 and 
4.0.5F and on a Sun Sparc SLC running SunOS 4.1.1. There are no real 
machine dependencies, though, so there should be no problems on other 
architectures.  
 
There is a timing program to test how fast the stuff runs on your 
machine. Here are some sample numbers: 
 
R4000 Indigo:	compress: 1.1Msample/sec, decompress: 1.7Msample/sec 
R3000 Indigo:	compress: 410Ksample/sec, decompress: 850Ksample/sec 
Sun SLC:	compress: 250Ksample/sec, decompress: 420Ksample/sec 
Mac-IIsi	compress   21Ksample/sec, decompress:  35Ksample/sec 
 
I'd be interested in numbers for PC class machines. 
 
Also included are some simple test programs that convert audio files 
to/from 4bit ADPCM samples. Rawcaudio/rawdaudio convert to/from raw 
16bit PCM files; sgicaudio/sgidaudio convert to/from SGI AIFF files 
and 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 to 
decide whether to compress or decompress). Oh yeah, the sun and sgi 
compressors will probably only compile on those machines. Also, for 
the 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, but 
unfortunately I have no way of testing the result (since it needs 
Solaris 1.somethingorother which I don't have). If the program does 
not work and someone fixes it I would like to get a copy. 
 
Finally, there is a uuencoded adpcm sound file of me saying "hello 
world" (with a cold) that you can use to test that everything works 
correctly. 
 
If you use this package I would like to hear from you. 
I am especially interested in people who can test interoperability 
with proven Intel/DVI ADPCM coders. I have tried to get the algorithm 
correct, 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) 263-0590 
 
They might be able to send back issues of their proceedings, I don't 
know. 
 
	Jack Jansen 
	Centre for Mathematics and Computer Science 
	Kruislaan 413 
	Amsterdam 
	the Netherlands 
 
	+31 20 592 4098 
	Jack.Jansen@cwi.nl