[sdiy] My New Project - PCSYNTH

[Gorka Garcia]

Not sure about the details of the display control done by the ZX81 (resolution, framerate)

Basically, the problem with audio is that you need to be feeding the DAC all the time at a fixed sample rate while you do the processing, whereas in video you normally can do by only updating the screen once you have finished processing (and waited for the time the next frame has to be displayed). In that sense, in audio you are restricted to do all the processing in a certain number of cycles so that you have samples available to feed the DAC, while in video you have more flexibility since it does not really matter if you keep the last frame on the screen for another frametime.

Basically, my conclusion is that the fact that the z80 can do video display does not imply it can do audio processing perfectly (not saying it can either, you just need to look at http://www.nullsleep.com/treasure/zynth80/ ). Audio seems to require a more clever programming than video. Hope my point is clear.

Gorka

--- Rainer Buchty <rainer at buchty.net> wrote:

From: Rainer Buchty <rainer at buchty.net>
Date: Tue, 7 Jun 2005 11:09:21 +0200 (CEST)
To: Gabriel Lindeborg <gabriel at lindeborg.org>
Cc: torpedo at demadrid.com, synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] My New Project - PCSYNTH

>That is all true. But consider a standard VGA display w. 640 by 480 
>pixels and a refresh rate of 25 pictures per second. The DAC frequency 
>of the signal would be 640*480*25=7680000 ie. 7,68MHz, right?

I wasn't even thinking of VGA timing but of good old ZX81.

Rainer


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