Path: utzoo!attcan!uunet!samsung!dali.cs.montana.edu!uakari.primate.wisc.edu!aplcen!haven!wam!dmb
From: dmb@wam.umd.edu (David M. Baggett)
Newsgroups: comp.sys.atari.st.tech
Subject: Re: spl or snd file format
Keywords: sound sample file format
Message-ID: <1990Oct16.213405.23309@wam.umd.edu>
Date: 16 Oct 90 21:34:05 GMT
References: <8928@cognos.UUCP>
Sender: usenet@wam.umd.edu (USENET Posting)
Reply-To: dmb%wam.umd.edu@uunet.uu.net (David M. Baggett)
Organization: University of Maryland at College Park
Lines: 33

In article <8928@cognos.UUCP> rossj@cognos.UUCP (Ross Judson) writes:
>Does anyone know the format of .spl or .snd files?  I am attempting to
>create samples in files, which I can play back with David Bagget's
>play.ttp.  

An excellent choice of software!  :-)

>My first guess was that the files are simply 8 bit data.  The sounds I
>get out aren't very good though, so I'm wondering if there's more to
>the format than I know.

The samples are 8-bit data, with no header and no tailer information.
The crucial point is that the samples are "8-bit unsigned" samples,
which means that the values correspond to voltages from 0 to +5  (so
I'm told).  A value of 0 means 0V, while a value of 255 theoretically
corresponds to +5V.

This is _quite_ different from the "competing" format, 8-bit signed,
wherein each sample is taken to be a signed voltage from -2.5V to
+2.5V.  To convert from unsigned to signed format you simply have to
subtract 128 from each sample.  To go the other way, you add.  (Sounds
simple, but try to figure it out by looking at the data files!)

Incidentally, the Hippo digitizer uses signed samples.  The "standard"
ST format is 8-bit unsigned.

To convert between them, get a copy of "convert.arc" from
atari.archive.umich.edu:/atari/newitems/  
The program hippo2st.ttp will convert 8bit signed to 8bit unsigned.
(Guess what st2hippo.ttp does....)

Dave Baggett
dmb%wam.umd.edu@uunet.uu.net