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From: cpenrose@sdcc13.ucsd.edu (Christopher Penrose)
Newsgroups: comp.sys.next
Subject: Re: Soundfiles
Message-ID: <17776@sdcc6.ucsd.edu>
Date: 25 Mar 91 21:56:58 GMT
References: <1991Mar24.195924.3238@cunixf.cc.columbia.edu>
Sender: news@sdcc6.ucsd.edu
Organization: University of California, San Diego
Lines: 29

In article <1991Mar24.195924.3238@cunixf.cc.columbia.edu> 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 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?

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