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
that 30kHz.
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.
.hc
¡El pueblo unido jamás será vencido!