Xref: utzoo comp.sys.ibm.pc:53385 rec.games.programmer:1990
Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!uwm.edu!uwvax!persoft!eda
From: eda@persoft.com (Ed Almasy)
Newsgroups: comp.sys.ibm.pc,rec.games.programmer
Subject: Re: Quality of PC sampled sound
Keywords: samples, sound, IBM-PC, Amiga
Message-ID: <1990Jun29.185638.2623@persoft.com>
Date: 29 Jun 90 18:56:38 GMT
References: <1990Jun28.015758.19188@ux1.cso.uiuc.edu> <1990Jun28.164522.2987@persoft.com> <22898@boulder.Colorado.EDU>
Distribution: na
Organization: Persoft, Inc.
Lines: 25

In article <22898@boulder.Colorado.EDU> wallwey@snoopy.Colorado.EDU (WALLWEY DEAN WILLIAM) writes:
>In article <1990Jun28.164522.2987@persoft.com> eda@persoft.com (Ed Almasy) writes:
>>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".

I think we must be talking about two different pieces of software.  The
program I was refering to (and which I disassembled and traced through)
changes the clock rate, but only at the beginning of playback.  I would
be interested in seeing one that changes it continuously, if only to
examine the algorithm.  Does anyone know where a copy might be available?

(let's take this to e-mail)