[sdiy] DCO amplitude with filtered PWM

Declare Update declareupdate at gmail.com
Sat Sep 1 07:55:06 CEST 2018

> PWM is harmonically equivalent to detuned sawtooths.

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? I do understand that the harmonic content of a saw is the same whether inverted or not, so it makes sense that their sums would be equivalent, but visualizing what they’d look like on a scope is yielding ... dissonance (hehe)

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? 

I realize I could just wait a week til I’m back with my computer and synths, but these long train rides really got me chewin’... thanks for bearing with me here! 


> On Aug 31, 2018, at 9:56 PM, Tom Wiltshire <tom at electricdruid.net> wrote:
> PWM is harmonically equivalent to detuned sawtooths. That this is true is demonstrated by the fact that one way to generate a PWM waveform is to mix a sawtooth and a ramp wave (e.g. inverted saw) and then tweak the relationship of the phases.
> What you describe with the heavy uP control of the waveform generation sounds like where the later CEM chips like the 3396 finished up, although perhaps you’ve got even further in that direction.
> Tom
> ==================
>       Electric Druid
> Synth & Stompbox DIY
> ==================
>> On 31 Aug 2018, at 07:40, Declare Update <declareupdate at gmail.com> wrote:
>> I built this because I had a thought a while
>> back that I could simulate detuned sawtooths with one integrator if I could control slope, reset rate, and reset level of a DCO with an MCU. I whipped it up in max to confirm it works, but haven’t gotten around to trying that specifically in the hardware, heh. I’ve found that this much flexibility is not necessary in most cases, though it does let me generate just about any waveform I’m patient enough to work out. 
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