Hola Richard, Robin, On Sat, 29 Jul 2000, Richard Atkinson wrote: > On Fri, 28 Jul 2000, Robin Harbron wrote: > > > Both the PRG and Mapping claim that pulse width=(register value/40.95)%, > > so that setting the pulse width to 4095 would get a duty cycle of 100%. > > It wouldn't be the first time they were wrong, of course... > > That is wrong; I've checked this with an oscilloscope. Either set the PW > registers to 0 and rely on the envelope generator at full volume for DC > offset, or use the zero frequency method as already described. Yeah. Presumably the pwidth value is just added to a running counter, with the high bits determining high/low. Robin, one thing to keep in mind with pulse waves is that they are "symmetric" about zero -- that is, a 20% duty cycle is identical (to the ear) to an 80% duty cycle. Except for a minus sign, they have the same Fourier transform (1 - h(x) versus h(x)). You can verify this with your ear, using a pulse width of, say, 256, and one of 4096-256. I think that pwidth=4095 is the same as pwidth=1. (Maybe you already knew this; professor Judd will now step down). I was just fiddling around with the tunesmith instrument editor, and I was suprised to see that with a zero frequency, a pwidth setting of 0 on voice three puts the oscillator output immediately at $FF; a setting of 4095 puts the output to zero. Are the outputs inverted wrt the register value? If not, then why does pwidth=4095 and freq=0 work for digis? Finally, I just observe that any waveform can be used to set the output value -- for example, using a sawtooth and a frequency of 1, I can set the freq to zero and halt the oscillator output at arbitrary values. Speaking of which... has anyone ever sampled some of the combination SID waveforms using a low frequency, like 1? Is it the same as at higher frequencies? It always seemed to me that a little Fourier analysis ought to be able to clear up the mystery of the combination waveforms. -Steve - This message was sent through the cbm-hackers mailing list. To unsubscribe: echo unsubscribe | mail cbm-hackers-request@dot.tcm.hut.fi.
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