[3-5] Ripping SID tunes
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Much information about ripping is provided at our Help page.
http://hvsc.c64.org/Help/index.html The calculation formula for the amount of cycles a C64 has is based
on the assumption that a processor cycle can be subdivided into fractions.
This is, on close inspection, not true.
One rasterline has exactly 63 cycles on a PAL machine, not 63.15, as
mentioned in that article. Hence, the total amount of cycles available
on a PAL C64 is 63 * 312 scanlines = $4CC8 (not $4CF8 as derived from
the algorithm using fractions).
Thus, the correct algorithm to get the CIA timer values for multispeed
tunes would be
( $4CC8 / n ) - 1
with n being the speed setting of the tune (n=2 if doublespeed, etc.)
Subtract one from the final result because the CIA timer is counting
backwards to zero. So if the CIA timer value is set to $2663 it actually
counts $2664 cycles until it reaches zero. Double that and you end up at
the original $4CC8.
Note, ripping SIDs requires some assembly language knowledge. Thus,
ripping SIDs is not always an easy task (but it isn't always hard,
either). The point we are trying to make is that if you do not plan
to rip the SID the correct way, then do not even bother ripping the
SID. In particular, do not cut off the end of the music data too early,
as this often means that the SID will fall out of synch either
in a portion of the tune, or on restart.
Pintaria traducir toda la info correctamente no ?.