On May 25, 2006, at 7:19 PM, Frank Barknecht wrote:
Hallo, Hans-Christoph Steiner hat gesagt: // Hans-Christoph Steiner wrote:
I should say, I forgot that PWM was used in synthesis some, so I was thinking about electronics and control when I was talking about PWM. That's why my PWM objects are tailored towards, but should work fine in the audio context too, unless you need the wandering DC offset.
The DC wanderer is not needed, but according to: http://www.soundonsound.com/sos/Mar03/articles/synthsecrets47.asp it generally is considered to be like this:
Note that Figure 3 shows a low-frequency amplitude modulation at the LFO speed (hence the downward and upward slope to the resulting PWM wave). Don't worry about this; the prominence of the modulation in the diagram is a consequence of the limited space available for the drawing. If the audio waves are pitched at a few hundred Hertz (somewhere in the middle of the piano keyboard) and modulated by an LFO running at a fraction of a Hertz, this modulation is of no significance, provided that you allow sufficient headroom to accommodate it. If you want, you can use a high-pass filter to remove it, but it's rarely worth the effort.
Aliasing/foldover is a much bigger concern with this naive kind of PWM/rectangle wave generation in Pd.
Aliasing is not so relevant for the quick and dirty PWM control
signal. But it would be nice to have a clean signal. I suppose I
should put a low pass to prevent that.
Or does someone have a better algorithm for a bandwidth limited PWM?
.hc
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