[PD] Re: [PD-announce] PWM in Pd
hans at eds.org
Fri May 26 13:01:25 CEST 2006
On May 25, 2006, at 7:24 PM, Martin Peach wrote:
> 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.
> For controlling things with PWM I think you'll need to modify your
> sound card if you want DC output. AFAIK they all have capacitors on
> the ouput to block DC. I find it easier to program a PIC to do the
> PWM and talk to it from PD using MIDI continuous controller
> messages for 14-bit resolution, or noteon with velocity meaning
> pulsewidth for 7-bits.
No, you don't need DC at all with PWM, unless you call the HIGH
section of the pulse DC. But since that section lasts in the range
of milliseconds to microseconds, I think its safe to call it AC. ;)
Actually the audio range of 20-20,000 is a good working range for
cheap PWM. High-quality PWM is much higher frequency. The Atmel
ATMEGA8 in the Arduino, for example, has three hardware PWMs which
operate at ~30kHz. That means in order to ensure its a real square
wave, it has to have a frequency response that covers much higher
The question I wonder about when using a sound card to output a PWM
control signal is whether you can reliably get a positive-only
voltage range, and not the usual -1 to 1 of audio.
¡El pueblo unido jamás será vencido!
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