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From: mir@opera.chorus.fr (Adam Mirowski)
Newsgroups: comp.sys.ibm.pc.misc
Subject: Re: Digtized sound thru IBM speaker
Message-ID: <8365@chorus.fr>
Date: 13 Mar 91 14:37:45 GMT
References: <4912@czech.sw.mcc.com>
Sender: mir@chorus.fr
Reply-To: mir@opera.chorus.fr (Adam Mirowski)
Organization: Chorus systemes, Saint Quentin en Yvelines, France
Lines: 20

In article <4912@czech.sw.mcc.com>, daneman@czech.sw.mcc.com (Michael Daneman) writes:
%% I have recently gotten some program that play MAC digital sound
%% through the regular ibm speaker (such as remac, sounder).  I am very
%% impressed with kind of quality this produces.  Does anyone have the
%% format for the sound files and the algorithm used for playing them?

The format is a stream of unsigned bytes, ie. 00h is -amplitude and
FFh is +amplitude on the output. No header. You have to guess the
sampling frequency.

The method is described in some ftp-able docs/sources. Basically, you
change the mode of the timer which drives the speaker. The 8254 is in
mode 2 (rate generator) normally, and you put it in mode 1 (or maybe
mode 4 or 5) to make it issue variable length pulses. You arrange to
issue them regularly and can thus obtain a pulse width modulation. The
longer the pulses, the higher the mean output voltage will be. One
author spoke about achieving a 6 bit resolution this way.
-- 
Adam Mirowski,  mir@chorus.fr (FRANCE),  tel. +33 (1) 30-64-82-00 or 74
Chorus systemes, 6, av.Gustave Eiffel, 78182 Saint-Quentin-en-Yvelines CEDEX