[PD] Recording question

Derek Holzer derek at umatic.nl
Tue Dec 18 12:06:39 CET 2007

Hi Tania,

are you able to record from two different soundcards simultaneously in 
any other application on your computer? I ask because this isn't usually 
the case in my experience. Many have dreamed of linking several "el 
cheapo" soundcards to get an inexpensive multichannel soundcard from 
them.  Two (or more) different soundcards have two different sample 
clocks and these won't be in sync, among the main problems. Google "el 
cheapo soundcard", or check here:


To see how this might be accomplished on Linux. There, it requires the 
hardware modification of removing the clock from one card and connecting 
it to the clock of one master card.

And I quote:

> The challenge in recording with more than one soundcard at once in any computer under any operating system is to make the cards syncronize. The actual sample rate of each card is depending on the crystal used in the card. To cut the component cost of consumer grade soundcards cheap crystals, with wider tolerances than those used in pro equipment, are often used. As a result, when using two cards at once one can have a real sample rate of 44.099 kHz in one card and a samplerate of 44.101 kHz in the other. This is no problem when recording with one card only, but the difference in the sample rates will cause phase shifts in the recording when using two cards. Phase shifts make the high frequencies of the recording e.g. cymbals sound bad. Further, not all audio drivers can drive cards that are not in exact samplerate sync.
> Some pro-cards come equipped with a link to connect multiple cards to run in sync. Consumer cards do not have this feature. This Howto describes a simple hardware modification to create such a synchronisation link between consumer grade cards. Without hardware modifications it is very difficult to ensure the cards are in sync. 

You haven't mentioned the operating system you are running, BTW...

Maybe other operating systems allow multiple (consumer) soundcard 
recording, I haven't tried. In PD, I don't think it's possible. If you 
had a way of getting your two IMics to be seen as one soundcard (the 
Linux el cheapo method), then you could try it.


tania habib wrote:
> Hi List,
> I have a question regarding a patch that I made for recording
> multi-channel audio.
> For the 16 channels, we are using Fireface 800 with an extension
> board. It works quite well!
> For a specific application, we are trying to use the two iMic's with a
> USB plug to record at least 4 channel audio.
> When I initialize PD and select the audio settings, it shows me two of
> these seperately in the option, the recording for one works but not
> for the other!
> The question is if I can use PD to record simultaneously from two
> different source from a single patch or somehow get the recording from
> both!
> regards,
> Tania
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derek holzer ::: http://www.umatic.nl ::: http://blog.myspace.com/macumbista
---Oblique Strategy # 94:
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