AlenK Posted July 21, 2013 Share Posted July 21, 2013 I came down pretty hard on the XW's pulse-width modulation implementation in a couple of posts a while back. I'm sure at least a few readers were thinking "What's his beef?" To clarify what I meant I have attached here a zip archive containing two files that demonstrate what PWM sounds like on the XW and what it is supposed to sound like. These are solo synth sounds.The first, "PWM Broken.ZSY", implements full-range PWM using oscillator 1. The second, "True PWM.ZSY" is a technique that simulates full-range PWM using two oscillators, one playing a sawtooth waveform and the other a ramp waveform. To compare them drop them in adjacent memory locations in the XW (they were created on an P1 but I believe they will also work on a G1) and alternate between them while playing note C4. (The patches only match on that one specific note).What you will hear from "PWM Broken.ZSY" is a distinct "graininess" as the pulse width is swept from minimum to maximum. In contrast "True PWM.ZSY" sounds very smooth. It also actually drops out briefly as both waveforms completely cancel at one point. That is unavoidable with this simulation and is arguably not ideal for a PWM sound. Note that I don't believe the "True PWM.ZSY" patch is of any real use primarily because the modulation rate of the pulse width varies linearly with pitch (it doubles every octave). The modulation rate of PWM is supposed to be the same for every note.Does the graininess make the XW's PWM unusable? Not if you keep the amplitude of PWM low (the examples were full range). But another problem becomes audibly apparent above about C5: aliasing. In my opinion the two artifacts combined render PWM useful only for making bass notes fatter. Maybe that's all Casio had in mind for it.PS. if you can find something I did wrong in the "PWM Broken" patch please let me know. I would be very happy to find out that PWM does work properly after all.PWM comparison.zip 3 Quote Link to comment Share on other sites More sharing options...
BrettM Posted February 12, 2014 Share Posted February 12, 2014 Can't the LPF be used to reduce the "graininess" and other artifacts? I agree that PWM-L and PWM-B sound better than PWM. Quote Link to comment Share on other sites More sharing options...
AlenK Posted February 13, 2014 Author Share Posted February 13, 2014 I gave your suggestion a try. What I got was just a duller sound with the same grainess and aliasing. The artifacts didn't go away. Like I said, PWM on the XW is suitable only for fattening up bass sounds IMHO. But for that one application it does work well. Maybe Casio will get it right in the XW's next incarnation. Despite my yapping about this problem it's really only a minor disappointment. I have moved on to bitch about other things. Quote Link to comment Share on other sites More sharing options...
BrettM Posted February 17, 2014 Share Posted February 17, 2014 Easing up on the depth of the LFO controlling the pulse width will reduce the nasties. Quote Link to comment Share on other sites More sharing options...
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