[sdiy] DCO amplitude with filtered PWM
declareupdate at gmail.com
Sat Sep 1 16:17:43 CEST 2018
awesome answers from both of you, thanks
richie, that is exactly the info I was looking for. thank you sharing it in detail. the “phase of harmonics” is something I’ve never thought about outside of school.
On Sep 1, 2018, at 9:09 PM, Richie Burnett <rburnett at richieburnett.co.uk> wrote:
>> PWM is harmonically equivalent to detuned sawtooths.
> Yes, in the most general case.
>> Are they really equivalent? I’m aware of the saw+ramp=pulse trick, but to get the common animated pwm wave out of that, you shift the phase forward then backward, which would be more like shifting the pitch up and then down, or am I totally wrong here?
> No. That is totally correct. The forward and backward phase shifting (pitch up /down) is an implementation aspect due to the typical triangle LFO waveform used to generate PWM.
>> I do understand that the harmonic content of a saw is the same whether inverted or not...
> No, the phases of the harmonics are different for a ramp vs sawtooth.
>> detuned saws, without one inverted, would not result in nearly silent “phase-y” sounds, as one might describe them. wide pwm, where the pulse becomes fairly narrow, have this high pass sort of sound going on (unsurprisingly), but does this also happen with detuned saw? my intuition says not, but maybe I’m wrong here. am I misunderstanding something?
> See my other reply.
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