Posted By
Luca
on 2023-02-14
10:12:58
 |  Re: TED Music Collection
The best and better desirable case of multispeed playback is the classic rastertime-equidistant PAL one, in which the callbacks are symmetrically placed: 156 scanlines for 2x, 104 for 3x, 78 for 4x and so on.
The alternative case is the one in which the coder did not place a symmetrical time per frame.
A third case includes various sub-cases of variable time between the callbacks, mostly due to a not stable code: a 2x tune may have a 50/50 different callback scanline, or a much complex cycle of different values, as closer as they are to the original behavior of that code, and usually I build up a table of values to be read at every frame in order to make it sound similar.
Similar cases can be found in the single speed players too, some tunes are slowed down by a machine's IRQ not shut down, some play with an average speed between all the different values of $FF0B read by the code frame by frame... Anyway those are all exceptions, and even in the multispeed sounds there's a common good usage of the rastercounting. They exist btw, and a comprehensive format shoud keep them in count too. The worst of all are the ones from Misfit, who uses to code some resulting sound from different parts of some horrible spaghetti-code, often deviated by the effects at that moment on the screen 
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