[pulseaudio-discuss] New user with questions on multiple USB sound devices

[Dewey Smolka]

Thanks for the reply, Tanu.

On Jan 29, 2008 5:02 AM, Tanu Kaskinen <tanuk at iki.fi> wrote:

> In this case I don't think you'll find much by using either
> method, though.

I had a look through the archives and you're right, I wasn't able to
find anything to answer the question.

>
> I tried to run jack on top of pulse, and it seems that it
> doesn't work at all because the pulse device doesn't support
> mmap access that jack needs. So we can forget about pulse -
> all I can do now is suggest you to take a look on Jack
> diplomat:
> http://mw-turing.culture.hu-berlin.de/mwiki/index.php/Jack_diplomat

I had a look at the link and it seems like this may be a possible
solution, but I wasn't able to get to the source code. I may try that
later if I can't figure out a better way.

But I'm a little confused as to why this wouldn't be possible. Maybe I
misunderstand how the pieces fit together, but it seems to me that it
should work.

Here's how I understand it: Pulse would sit on the bottom and address
the hardware directly -- in this case call it usb0 (the Omega) and
usb1 (the MX200). Usb0 would have 4 sources and 2 sinks while usb1
would have 2 sources and 2 sinks. Pulse would combine these into a
virtual device with 6 sources and 4 sinks that would be addressed as a
single device by Alsa.

Jack would then address the virtual device through Alsa. It seems to
me that Jack wouldn't even need to be aware of Pulse, since it would
be communicating only with Alsa, as it normally does.

Is this how Pulse works? Or conversely, is it possible to make Pulse
work like this?

I also understand that there's no way to sync the clocks between the
two devices but I don't think that's a significant problem. The two
units would never be operating in parallel. The Omega would always be
the primary audio interface, while the MX200 would only be a
send/return loop.

Any thoughts? Do I understand the architecture correctly or is this
really not possible?

Thanks in advance,

Dewey