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2007-07-09 18:05

McMeatLoaf

Registered: Jan 2005
Posts: 108

4-bit, 3-chan PWM

I already know about some music with PWM (e.g. "Ragga Run" by Danko). I know you can get up to 8-bit or something (although AFAIK you can't get much better than 16khz at 6-bit), but is there any examples of using just 4-bit PWM, but in 3 channels, which basically creates a 3-chan MOD?
And if it's possible, how high sample-rate can you get? (20khz?)

Yes, the post above may seem confusing...

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2007-07-11 13:33

Graham
Account closed

Registered: Dec 2002
Posts: 990

The oscillators max. base frequency is limited to 4 kHz, but this doesn't limit the samples in any way.

2007-07-11 16:07

Frantic

Registered: Mar 2003
Posts: 1648

FM stuff is surprisingly little explored on the C64. Perhaps because the "default SID usage" itself has been interesting enough for many people, while other platforms like Amiga are more likely to be used for FM stuff. Another reason for CPU hungry audio code like FM synthesis to be little explored on the C64 is of course that many C64 players are meant to be used together with game or demo code.

Also, as commonly pointed out by me and others, there has been surprisingly little attempts at doing SID stuff that requires lots of CPU in general, apart from playing samples. I mean, not only FM stuff have been under-explored, but CPU heavy audio hacking in general.

2007-07-11 21:21

MagerValp

Registered: Dec 2001
Posts: 1078

YES! We have lots of musicians/coders, I'm sure there's lots of untapped potential in the SID.

2007-07-12 00:56

Oswald

Registered: Apr 2002
Posts: 5095

well I wouldnt say that, there is mod player, polly tracker, reflex tracker, voodo people, each one pretty much maxxes out the digi possibilities of the c64 imho.

2007-07-12 06:53

Ninja

Registered: Jan 2002
Posts: 411

It's not the CPU making the limit this time. For a higher resolution, you need to produce a longer squarewave. Obviously then, you can produce less of those squarewaves per second. You could do something like 6.5 bit at ~10Khz, though. :)

2007-07-12 08:27

MagerValp

Registered: Dec 2001
Posts: 1078

Quote: well I wouldnt say that, there is mod player, polly tracker, reflex tracker, voodo people, each one pretty much maxxes out the digi possibilities of the c64 imho.

Yes, digis are maxed out. SID is not. Just look at the custom waveforms we got the other year, more stuff is bound to be hiding in there.

2007-07-12 09:11

Frantic

Registered: Mar 2003
Posts: 1648

@Oswald: Well, as Magervalp pointed out, I was referring to other CPU hungry SID hacking approaches APART FROM Sample playing (which is what the stuff you mention is all about).

On the other hand I wasn't necessarily referring to hardware intricacies of the kind SounDemon explored with his "new waveforms" a while ago (resetting the noise "oscillator" by tricky register settings), as referred to by Magervalp. Of course, there may still be some potential for such stuff, but it was not mainly what I was thinking about in this case.

Rather, I was talking about stuff like, for example, using timers in general for resetting the testbit periodically in order to change the shape of waveforms, combining waveforms in a controlled and timed way in order to produce controlled additive and subtractive results (which can in fact produce FM-like or sample playing like results) and whatever. Other stuff would be CPU hungry modification of the envelopes in order to gain complete control of them over time (Alih did some experiments similar to this I think, with "software oscillators", like sines, "controlling" some SID parameters other than just vibrato/frequency, which do not have direct hardware support for being controlled in such ways, but can be controlled in that way using CPU hungry code), and so on. However, the borders between different approaches are fuzzy of course. Multi speed music could be argued to be able to achieve much of the "CPU hungry" potential, but not all, if we think about the more exactly timed stuff I mentioned, which may require one or several CIA timers (or timed code) running at different speeds, changing dynamically over the time as the music plays different frequencies and so on.

etc etc..

Anyway, the topic was about sample playing, so I guess I am sliding off topic here. Sorry.

2007-07-12 13:28

McMeatLoaf

Registered: Jan 2005
Posts: 108

Quote: @Oswald: Well, as Magervalp pointed out, I was referring to other CPU hungry SID hacking approaches APART FROM Sample playing (which is what the stuff you mention is all about).

On the other hand I wasn't necessarily referring to hardware intricacies of the kind SounDemon explored with his "new waveforms" a while ago (resetting the noise "oscillator" by tricky register settings), as referred to by Magervalp. Of course, there may still be some potential for such stuff, but it was not mainly what I was thinking about in this case.

Rather, I was talking about stuff like, for example, using timers in general for resetting the testbit periodically in order to change the shape of waveforms, combining waveforms in a controlled and timed way in order to produce controlled additive and subtractive results (which can in fact produce FM-like or sample playing like results) and whatever. Other stuff would be CPU hungry modification of the envelopes in order to gain complete control of them over time (Alih did some experiments similar to this I think, with "software oscillators", like sines, "controlling" some SID parameters other than just vibrato/frequency, which do not have direct hardware support for being controlled in such ways, but can be controlled in that way using CPU hungry code), and so on. However, the borders between different approaches are fuzzy of course. Multi speed music could be argued to be able to achieve much of the "CPU hungry" potential, but not all, if we think about the more exactly timed stuff I mentioned, which may require one or several CIA timers (or timed code) running at different speeds, changing dynamically over the time as the music plays different frequencies and so on.

etc etc..

Anyway, the topic was about sample playing, so I guess I am sliding off topic here. Sorry.

If you're off topic? Hmm, it's OK to me, although a whole discussion about "new waveforms", CPU-intensive SID tricks and such would probably need its own topic. :)

2007-08-02 22:30

McMeatLoaf

Registered: Jan 2005
Posts: 108

OK, this may be bumping, but anyway:
Is it possible to change the CIA timers while a tune plays, so you can e.g. have one channel at 6x and another at maybe 8x, and then change the values to e.g. 9x and 12x?

If so, wouldn't it be possible to play some "notes" by using very tight loops (e.g. flipping from 400 to 0-16 hz)?

2007-08-03 06:50

Oswald

Registered: Apr 2002
Posts: 5095

you can have only one interrupt based on cia timers.

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