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Laxity
Account closed
Registered: Aug 2005
Posts: 459 |
Noise generator shutdown
As far as I remember the noise generator of the sid shuts down completely if a value of $9x (where x>=$00 & x<$08, not sure about $08 to $0f) is put into the waveform selection byte of any channel on the SID. Now the noise generator restarts when the SID recieves an osc. reset (bit 3 of the waveform selection byte) in any channel. I was wondering if this bug persists on the 8580 (where waveform mixing should be a lot better), or if this is only an issue on the 6581, never had hands on a 8580 myself. This bug is not emulated in reSid (or at least the versions I've tested), and is therefore not a reference in this question. Anyone knows this? The bug (if it is such!) might even occur when other waveforms are mixed with noise.. dunno about this, as my 64 is dead so I can't really investigate! |
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Frantic
Registered: Mar 2003
Posts: 1661 |
I think it's the same. At least SounDemoNs tune (which uses this "feature" to make some weird waveforms) in the Dekadence demo called Pico works on the 8580 too, so.. |
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Radiant
Registered: Sep 2004
Posts: 640 |
This topic is covered at length in SounDemoN's article in VN45. |
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Laxity
Account closed
Registered: Aug 2005
Posts: 459 |
A link would be cool |
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Oswald
Registered: Apr 2002
Posts: 5126 |
Vandalism News #45 |
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Laxity
Account closed
Registered: Aug 2005
Posts: 459 |
Oh.. That's what VN means... |
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zdzisek
Account closed
Registered: Apr 2002
Posts: 33 |
The noise waveform lockup is mentioned in reSID in wave.h:
// Combined waveforms including noise:
// All waveform combinations including noise output zero after a few cycles.
// NB! The effects of such combinations are not fully explored. It is claimed
// that the shift register may be filled with zeroes and locked up, which
// seems to be true.
// We have not attempted to model this behavior, suffice to say that
// there is very little audible output from waveform combinations including
// noise. We hope that nobody is actually using it.
It's likely that the effect is exactly the same on 8580, since combining waveforms seems to shortcut the waveform outputs on this chip as well. |
