[PD] Re: [PD-announce] PWM in Pd

Martin Peach martinrp at alcor.concordia.ca
Thu May 25 23:18:04 CEST 2006

padawan12 wrote:
> Very true. The DC blockers in most s/c are going to be limiting.
> But there's no reason to assume people using Pd for more serious
> experimental applications won't use correct DAC hardware. I think
> its very exciting to see the emergence of Pd as an application 
> for wider research in engineering, rapid prototyping etc and I
> applaud HC for thoroughness and attention to detail in the code.
> The beauty of sw over hw is extensibility, on a 64 bit system
> you could use this to position a radio telescope or whatever, far
> beyond the grain you'd ever get with 7bit microcontrollers.

The grain depends on the clock speed, not the bus width.
MIDI is 7-bit, the micro is 8-bit, but nothing stops you from 
implementing a 64-bit register on a microcontroller, but you'd need 10 
MIDI messages to fill it. As you say, it's all in the software. A 64-bit 
system just calculates faster, it doesn't do anything an 8-bit system 
can't, given enough time. A lot of PICs have a 10-bit PWM module 
built-in but it's only one channel.
In software it's not too hard to make an 8-channel 16-bit PWM machine 
using an 8-bit microcontroller such as a PIC16F628 for less than the 
cost of a soundcard. The software method will have more jitter though 
unless you're careful to write code that executes in equal time for 
every possibility.


> On Thu, 25 May 2006 13:24:16 -0400
> Martin Peach <martinrp at alcor.concordia.ca> 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.
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