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From: wallwey@snoopy.Colorado.EDU (WALLWEY DEAN WILLIAM)
Newsgroups: comp.sys.ibm.pc,rec.games.programmer
Subject: Re: Quality of PC sampled sound
Keywords: samples, sound, IBM-PC, Amiga
Message-ID: <22898@boulder.Colorado.EDU>
Date: 28 Jun 90 22:41:18 GMT
References: <1990Jun26.013548.246@eng.umd.edu> <1990Jun28.003451.1287@persoft.com> <1990Jun28.015758.19188@ux1.cso.uiuc.edu> <1990Jun28.164522.2987@persoft.com>
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Reply-To: wallwey@snoopy.Colorado.EDU (WALLWEY DEAN WILLIAM)
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In article <1990Jun28.164522.2987@persoft.com> eda@persoft.com (Ed Almasy) writes:
>If the PC had a "control everything" OS, then a program like the one in
>question could tell the operating system that it needed exclusive access
>to the resources, the operating system could tell the other apps/drivers
>to shut down for a moment, and we could have quality sound without
>crashing the whole machine.  As it is there is very little arbitration,
>and programs are constantly stepping all over each other when they try
>to optimize performance.

You are right all sound request should be handled through the OS, but to do
simple 8-bit sound, it should not take your whole computer (see below),
even if you decide to do the proper support through the OS. It would be
much easier for the PC world just to add (standardize on) a $5 D to A converter.

>What exactly is "digital-to-analog conversion by time multiplexing"?? I
>don't know if you know anything about the program under discussion (you
>don't seem to), but there are no analog operations involved.  It clicks
>the speaker at a rate determined by the data that you feed it - purely a
>digital operation.  There is no support for analog sound in the PC.
>

I don't think you know what you are talking about!  If I understand it
right, the program in question basically uses Pulse Length Modulation
(also goes by the name of Pulse Code Modulation or Pulse Duty
Modulation)
to simulate an analog channel on the 1 bit 'digital' channel.  It is too
complicated to explain how and why it works here(mail me if you really
must know or in a more specific news group--(I think you could talk
about this in sci.electronics), but basically the
microprocessor's complete attention is needed to do it. 
The reason this is, is because the microproccessor must change the duty
cycle of the clock chip every "sample".

-Dean Wallwey


******************************************************************************
*-Dean Wallwey   wallwey@snoopy.colorado.edu  or  wallwey@128.138.238.103    *
*"If people drove cars like they run computers, 5% of the driving populating *
*would die every business day in automobile accidents!"                      *
* #define DISCLAIMER \                                                       *
* The above comments are my own and not necessarly that of my employer or\   *
* school.    grammer, spelling errors, real heavy flames > NULL              *
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