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From: ldo@waikato.ac.nz (Lawrence D'Oliveiro, Waikato University)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Mixing Sounds
Message-ID: <1991Jan31.182519.2871@waikato.ac.nz>
Date: 31 Jan 91 05:25:18 GMT
References: <15980@reed.UUCP>
Distribution: na
Organization: University of Waikato, Hamilton, New Zealand
Lines: 20

Just a note that if you're feeding sound samples direct to the standard
Mac sound output hardware, it expects the numbers to be in what I would
call "excess-128" form, rather than twos-complement form. To convert
one to the other is quite simple: just flip the top bit of the byte
(exclusive-or with 128).

So if you want to do your own mixing on sound data, you have to convert
the data to twos-complement form, do the addition and shifting, and
then convert it back.

As for dynamic mixing in 6.0.7, that only works on machines with
the Apple Sound Chip. Based on my initial *tentative* experiments,
I'd say that members of the Mac II family (including the LC) can
manage 4 channels max. The Portable, even though it has the ASC,
can only manage one.

Lawrence D'Oliveiro                       fone: +64-71-562-889
Computer Services Dept                     fax: +64-71-384-066
University of Waikato            electric mail: ldo@waikato.ac.nz
Hamilton, New Zealand    37^ 47' 26" S, 175^ 19' 7" E, GMT+13:00