Re: C64 music player source

From: Levente Hársfalvi (
Date: 2000-02-03 12:35:57


> The 'scaling factors' I was referring to were for the pitch. NTSC machines
> play 3.8% higher than PAL machines, and a semitone is 5.9% increase in
> pitch, so they would sound *horrible* together if uncorrected. The ADSR
> values cannot be compensated of course, as the resolution of Bob Yannes's
> lookup table is far too coarse, but there's a reason for that - the ear is
> not nearly so sensitive to ADSR timing or even filter cutoff as it is to
> oscillator pitch. I'm willing to bet that the routines will sound fine
> with ADSR left as they are. I don't think the filter cutoff frequency is
> derived from a clocked source, but rather a voltage-controlled filter with
> an 11bit D/A convertor. Thus the cutoff frequency is not affected by bus
> clock.

I'd confirm on this. The SID card for the Plus/4 runs at the single
clock of the Plus/4 (885Khz), I think it is a quite heavier difference
than the diff between the PAL/NTSC C64. When unchanged, a C64 music
plays almost one note lower on the thing :-(. With a proper modified frq
table, it becomes correct. The filters are unaffected, that's for sure.
The ADSR difference becomes sometimes significant, but I'd doubt if the
same applied to the NTSC C64 (at least, because it's actually faster
than the PAL C64, whereas the Plus/4 SID is slower).

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