[PD] Cheap multi-channel audio solution?

William Huston williamahuston at gmail.com
Sat Nov 28 03:51:39 CET 2015

Is it possible on Linux and/or Raspbian to take have
two USB audio cards and reference them like:

[dac~ 1 2 3 4]

Where 1,2 belong to soundcard A
and 3,4 belong to a soundcard B?

*The reason is that apparently there is massive*
*price gouging on multichannel USB interfaces.*

For example, a Griffin iMic costs $40/USD.
This is 2x2 of crystal clear audio.
So 4x @ 2x2 = 8x8.

So the price for an 8x8 should be $40x4=$160, right?
Or less. Generally you should get a price break
when buying more of the same.

Yet it seems that most 8x8 audio interfaces
are in the range of $600-$900!! (USD).
This seems like 4x to 6x more money than it should be.

So multiple $40 2x2s would be a very cheap alternative
to getting a single 8x8. If it works. (if PD supports it).

PS: in case you don't know, USB 2,0 supports lots of audio!
 I was worried about saturating USB bus, and having audio compete for live
data from MIDI controllers. But no worries!

I just did the calculation.
*Max practical from USB 2.0 is 35 MB/s*.
2 channels of 24 bit (3 bytes/sample) audio at 48khz
= 2x3x48k
=288kB/s for 2 channels.


* ~122 pairs of audio = 243 total channels possible on USB 2.0. Wow!
Streaming audio may have some overhead, but even if you knock off 1/3 of
that, still leaves a lot of room.*

*USB 1.1 would be 243/40 = 6 total channels. (e.g., 2 in, 4 out).*

*So you definitely want to be running USB 2.0 if you are running 2in x 2out
+ midi controllers. *
I know lots of people using USB audio on the Raspberry Pi report having
problems running at USB2.0 "High Speed" = 480 Mbit/s, and have to set their
interface to USB 1.1. (12 Mbits/s). But I am so-far able to run at full
USB2.0 speeds with my Pi-2 and the Griffin iMic.

The Pi-2 will DEFINITELY keep up audio-wise, as my latest patch (12-channel
flanger) has at least 12 discrete channels of audio simultaneously at one
point, but there are many more internal nets
running audio.

I think most complex patches could easily have 24-50 internal nets running
audio. Which means even on a Pi-2, PD can definitely do complex stuff and
still easily support e.g., 8in x 8out.

So the theory is all there--- has anyone done it?

(Cheap multi-channel audio with PD over USB 2.0
using multiple sound cards... or any other solutions???)


May you, and all beings
be happy and free from suffering :)
-- ancient Buddhist Prayer (Metta)
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