Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!apple!uokmax!d.cs.okstate.edu!unx2.ucc.okstate.edu!minich
From: minich@unx2.ucc.okstate.edu (Robert Minich)
Newsgroups: comp.sys.next
Subject: Re: Soundfiles
Message-ID: <1991Mar26.004133.4930@unx2.ucc.okstate.edu>
Date: 26 Mar 91 00:41:33 GMT
References: <17776@sdcc6.ucsd.edu>
Organization: Oklahoma State University Computer Center
Lines: 39

kasdan@cunixa.cc.columbia.edu (John Kasdan) writes:
! What is a reference for the format of the Soundfiles?  From the
! on-line documentation, I get the impression that data is stored in the
! form of 1 byte which is interpretted [sic] by something called mulaw. How
! do I find out what all this means?  To be more specific, I would like
! to be able to get my hands on data in pure amplitude form, so as to be
! able to do FFT work on it.  Like, is there some form of conversion to
! 16 bit format, and would that do what I want?
 
by cpenrose@sdcc13.ucsd.edu (Christopher Penrose):
| look at the header files in /usr/include/sound.  Here is an excerpt from
| soundconvert.h:
| 
| unsigned char SNDMulaw(short n);
| short SNDiMulaw(unsigned char m);
| /*
|  * Routines to convert from 8 bit mulaw sound to/from 16 linear sound.
|  * SNDMulaw returns the mulaw value for the given 16 bit linear value,
|  * and SNDiMulaw returns the 16 bit linear value for the given mulaw value.
|  */
| 
| soundstruct.h will give you some info on the header that is prepended to 
| each NeXT soundfile.  Look at the on-line documentation again.  It is
| very helpful. 
| 
| Christopher Penrose
| jesus!penrose  

How about a reference that explains mulaw encoding for those of use
without these info sources. I don't have access to a NeXT (still too
expensive at this time...price is right, wallet is wrong...) but I want
to know how it works.

Thanks.
-- 
|_    /| | Robert Minich            |
|\'o.O'  | Oklahoma State University| "I'm not discouraging others from using
|=(___)= | minich@d.cs.okstate.edu  |  their power of the pen, but mine will
|   U    | - "Ackphtth"             |  continue to do the crossword."  M. Ho