Posted By
MMS
on 2014-08-04
17:19:31
 |  Re: Tracker instruments
I spoke with Copas on FB few months back. He was a friend or so of Pigmy, and they both lived in Zalaegerszeg. I recently worked there for 1 year too, and accidentally met with Copas.
He showed me the 3 channel digi player at the Univertsity (BME), we lived on the the same floor. At that time I made my "raytrace" gfx, and he programmed the digi player at the same time (full multimedia, yeah!)
EDIT: Pigmy and Copas discussed the details at Copas flat and both made parts in that.
Copas ripped a sample from Microdrums, defined it as "baseline" and wrote a BASIC program to resample the samples in advance. The sounds were not calculated "on the fly" , but stored in the memory. They made only channels and limited samples to fit into 16KB.
As Csabo highlighted below, it is that linked PRG. Time machine rulez! :-)
It run with a blank off screen, and played a Michael Jackson tune. The sound output was rather straighforward: added together the instruments current volume to each other then divied by 3, and transcoded to fit to the volume register.
So, it was a PWM, and a kind of tracker player without editor, even if very simple and very staighforward. As I remember it was pretty noisy (4 bit samples), and I think the 3 channel could produce worse result than the 4 due more complex maths. But it was a fantastic piece of code at it's time (1993) as multi track playback was as Amiga at that time, and my 286 16Mhz also badly performed later on tracker file playback on speaker(1bit) or Covox card (8bit) too. Not saying +4 is better 
As visible on Youtube (and discussed also ), the 3.5Mhz ZX Spectrum could also do this, even with 4-6 channel. 1bit rulez! But 8 bits can be better
https://www.youtube.com/watch?v=QZnOd_f9YjQ
So the theory: very short 8 bit samples, add 4 channel current volume to each other, divide by 4, push to User Port Covox. I dropped Ferranti, as my simple ZN728E8 costs a lot now, maybe I can sell my Covox for >100USD now
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