[PD] OSX and multiple sound devices

derek holzer derek at x-i.net
Fri Apr 14 23:51:17 CEST 2006


Hi Tim,

it's quite difficult to get any application to use multiple soundcards 
at the same time for output. Or to use multiple input devices as well. 
You can even choose a different device for input and output, that 
usually isn't an issue. The reason being that, even though the output 
devices might all run at the same sample rate, they have different 
timing crystals and they will eventually drift out of synch just enough 
that the application won't know what to do anymore and will crash. 
That's why JACK and most every other sound driver only support one 
interface at a time.

The only way this could really work is if the audio devices are 
hard-synced somehow. That means one is the Master and gives the sample 
timing to all the others. Expensive soundcards can do this via digital 
connections, but not normal laptop/bluetooth/etc chipsets. If you Google 
up "ALSA + el cheapo", you'll find some hacker-types that wanted to do 
this with Linux ALSA drivers and a bunch of $25 Soundblasters to make a 
budget multitrack system. The only way they succeeded was by removing 
the clock crystal from all the cards except one, and soldering 
connections from that crystal to all the others. An "el cheapo" 
solution, but not one that would work in your case with Bluetooth 
devices. Maybe this gives you ideas, maybe not...

best,
d.

Ti Bo wrote:
> 
> Hi,
> 
>   has anyone had any (successful!) experience using multiple soundcards
> in PD under OSX? I am trying to use several devices (I can see them using
> pd -listdev from the command line) by adding the command -audiodev 2,3,5
> to the startup and I am only getting the first device.
> 
> Just to make things more complicated, the first two devices are Bluetooth
> headsets (both have been tested alone and work) and the third device is
> the virtual device Soundflower. I have tried to use Jack but the
> Jack manual explicitly says that Jack will only support one hardware
> device at a time!
> 
> Have I managed to corner myself into an impossible situation where the
> OSX version of Pd can only deal with one hardware device at a time, 
> regardless
> of what it seems to be saying on the command line help? Or is there a
> way forward?
> 
> I hope someone can help,
> 
> cheers,
> 
> tim
> 
> 
> -----    Tim Boykett  TIME'S UP::Research Department
>  \ /   Industriezeile 33b A-4020 Linz Austria
>   X    +43-732-787804(ph)   +43-732-7878043(fx)
>  / \  tim at timesup.org    http://www.timesup.org
> -----
> http://www.timesup.org/fieldresearch/setups/index.html
> 
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-- 
derek holzer ::: http://www.umatic.nl
---Oblique Strategy # 60:
"Don't be afraid of things because they're easy to do"




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