[sdiy] Dumb PWM question

ASSI Stromeko at nexgo.de
Wed Feb 27 20:28:18 CET 2008


On Dienstag 26 Februar 2008, jbv wrote:
> well, the result might sound awfull, that's a possibility...
> but PWM on square waves sounds good, so may be it's worth a
> try with other waveforms and "natural" sounds as well...

"PWM" on a triangle/saw waveform is musically useful.  However the 
triangle wave is too sine-like, so the perceived loudness through 
modulation is changing quite a bit if the ampliztude is held
constant.  When I made a wavetable for the KOMPLEXER VST for Saw PWM I 
also added another one with spectral enhancement so that the triangle 
wave actually is a polynomial shaped waveform.

http://Synth.Stromeko.net/Tuning.html#Spectra

I've also written up some notes on how to control an integrator VCO to 
provide saw - triangle - reverse saw modulation, but it never made it 
to breadboard...

http://Synth.Stromeko.net/DIY.html#SawWM

This time compression/expansion thingy you mentioned should in principle 
work if you start with the expansion part (filling up a scannable delay 
line with the not-yet needed samples) and then compress until you again 
reach the beginning of the delay line.  To do this synchronized to the 
frequency however requires additional delays of minimum one period or a 
priory knowledge of the frequency of the input signal.  You should 
quite likely remove the DC component that is an almost inevitable 
result of doing it like this.


Achim.
-- 
+<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk]>+

SD adaptation for Waldorf rackAttack V1.04R1:
http://Synth.Stromeko.net/Downloads.html#WaldorfSDada



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