#1887 6581 pulse + sawtooth - incorrect samples for oscillator MSB = 1

[Dag Lem]

The 6581 pulse + sawtooth samples were obtained around 25 years ago. At the time, it was not known that the oscillator MSB can be zeroed via combined waveforms. The following program takes this fact into consideration, and obtains correct samples for the complete waveform:
https://github.com/daglem/reDIP-SID/blob/master/research/pulse-saw.a65
https://github.com/daglem/reDIP-SID/blob/master/research/pulse-saw.d64

It would be helpful if others could run the .d64 to obtain samples from different 6581s. The 6581 samples in reSID are comparatively strong (more non-zero values than average), and it would be nice if we could get samples which more or less match the existing ones (for MSB = 0).

[Dag Lem]

Here are the samples I got from the machine I had set up, converted for inclusion in reSID:

https://github.com/daglem/reSID/blob/master/src/wave6581_PS_.dat
https://github.com/daglem/reSID/blob/master/src/wave6581_PS_.h

These are good enough, and can be replaced later if someone comes up with "better" (stronger) samples.

[gpz]

updated the sample in r43932

leaving the ticket open since we still need more/better samples :)

[Leandro Nini]

BTW, shouldn't this be done for ST and PST too? Every combination that include sawtooth, on 6581, is affected by the problem.

[gpz]

BTW, shouldn't this be done for ST and PST too? Every combination that include sawtooth, on 6581, is affected by the problem.

good question!

[Dag Lem]

Good point!

Here is an updated sampling program for all combined waveforms (takes forever to run, unfortunately).

https://github.com/daglem/reDIP-SID/blob/master/research/combsample.a65
https://github.com/daglem/reDIP-SID/blob/master/research/combsample.d64

[gpz]

Forwarding from Trurl

Here are the pulse+saw test results attached. I renamed the files to keep track
of testing progress, I suppose this won't hurt.
3 of the sids had broken filters, those are the "broken" files. Discard those if
their results are bad.

Some of these chips are the same which I used back when alankila made the
resid filter curves :) Would be nice to hear how these compare to other chips
tested!

[gpz]

@daglem have a look :)

[Dag Lem]

• 'broken r4ar 3789.dat.txt' and 'cbm 4383.dat.txt' are almost identical to the chip I tested.
• 'broken r4ar 3488.dat.txt' is closest to (slightly weaker than) Andreas Boose's 6581 0683.
• 'broken 0384.dat.txt' seems to have extremely strong samples.

I guess the r4ar 3488 would be the best replacement in reSID.

[ltx128]

Test results (combsample.d64) for the 6581 in my C64 attached. It has quite lame combined waveforms.

[Dag Lem]

Samples (combsample.d64) from lots of chips from Trurl:

Hi!

Here are the new results for my chips, organized in directories this time.

Trurl