[PD] Playing and recording simultaneously

[Mathieu Bouchard]

On Sun, 4 Jul 2010, Martin Peach wrote:

> As long as they are on the same card, they will be in perfect sync at 
> the clock level unless you have some really unusual hardware. This is 
> because the same clock is used for A/D and D/A. Usually they are on the 
> same chip and the data from the ADC is clocked out using the same clock 
> that loads the DAC.

Can you just explain to us why sync has to be done when you have two 
soundcards that are supposed to be sending you the same number of blocks 
per second ?

I mean, for example, suppose a soundcard that is nominally set at 44100 Hz 
is actually running at 44098 Hz ; then what happens to Pd objects that 
depend on the samplerate (such as [osc~], [lop~], etc) ? Do they use 
44098, or 44100 ? that would be the same as whatever [samplerate~] says, 
but somehow, it always says exactly 44100.000 ... why ? Is it because my 
soundcard's clock is that much accurate ? (it's a cheap on-board thing)

I recall seeing precisely "44098 Hz" when my soundcard was an ISA 
Ultrasound (Gravis) some 5-10 years ago, but I don't recall whether it was 
at Pd's startup, another programme's startup, or both.

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| Mathieu Bouchard, Montréal, Québec. téléphone: +1.514.383.3801