Phase mod with PWM

[harry bissell]

Note that unless there is another Non-PWM waveform to compare with, it
doesn't matter if you have Triangle or Sawtooth based pulses... they will
sound exactly the same... With a single wave there is no phase reference
point so you can't hear it... You may get different results if you mix in
some fixed waveform though (like a sine, triangle, or ramp...)

:^) Harry

I like to put a simple LPF to decrease the amplitude automatically when the
mod wavform gets too fast... this changes a Triangle mod to a Sine
(eventually)

Tony Allgood wrote:

> Hi all,
>
> Is there a way of generating PWM without the phase modulation that seems
> to accompany it? I can understand that generating your PW from the saw
> output would generate a phase modulated signal. I believe, using a
> triangle wave, this should not be so. However my experiments have found
> that it does indeed produce a perceptible frequency shift as well.
>
> My poly's CEM3340 VCOs sound terrible if the PW modulation is deep and
> fast, just too much vibrato. I think the 3340s use the saw to generate
> the pulse out. My best workaround is to use a sine LFO, but you will
> still get a PM that is determined by the differential of the modulating
> waveform. Other than adding a differentiated sine (-cos) to the VCO's FM
> input, with approprate scaling, is there anyway to make deep fast PWM
> sound more pleasant?
>
> Regards,
>
> Tony Allgood  Penrith, Cumbria, UK
>
> Rack mounted moog filter and the TB3030 SuperBassline projects:
>
> http://www.techrepairs.freeserve.co.uk/