[sdiy] Pulse Width Modulation sampling??

[Mark Smith]

> Hello everyone,
> I read somewhere out there, about how people used to
> use pulse width modulation to create sort of
> samples/(audio redcordings?) for the commodore 64.
> 
	I think you are talking about mod files. These were something like a 4 channel sound source - probably done by the SID chip using PCM modulation (unless someone corrects me). Some of the best files I recall were public domain demos done on the amiga.

	I used to have a dos mod file player and the hardware interface was a homemade parallel port sound card. This was basically just an RC network from what I remember with a headphone socket on.

	The sounds were average as the sampling frequency was very low. I seem to remember also that only 4 voices/ notes at a time were used but the sound list could be huge.

> Does anyone know more about this?  Is it possible,
> using this technique to create audio samples that play
> via analog oscillators?  and what exactly is the
> difference between pulse width modulation and pulse
> code modulation (as seen written on old casio's and
> the like)
> 
	PCM is how modern DAC's work, streams of 1's and 0's are integrated to a DC level. PWM is generally a fixed frequency and the pulse width changes - you could integrate this to a dc level and by changing the mark space quickly generate audio, but then this is practically PCM.

	Try looking delta sigma modulators or class D audio amps. 
>  
> 
	mark