Re: [LAD] USB2 audio?! (Re: Alesis AudioLink)

Hi Paul

> On Thu, Jul 9, 2009 at 8:03 PM, Jonathan
> Woithe<jwoithe@email-addr-hidden> wrote:
>
> > AFAIK FFADO got started through the cooperation of one or two vendors and as
> > momentum has built additional vendors have come on board to a greater or
> > lesser extent. I expect something similar will have to happen for
> > professional USB2 audio devices to be generally supported under Linux.
>
> This misses out on the most important step in the evolution of FFADO.
>
> Before FFADO was Freebob, an open source implementation of software to
> support the BeBob API. Freebob was a project that was started by
> someone who worked for the company that developed the Bebob chipsets
> (Bridge Co.) ...

Ok, I should have included a little more detail. By "FFADO" in the above
paragraph I was referring to the FFADO/FreeBoB combination. BridgeCo was
indeed one of the cooperative companies I was referring to. I gave the
brief three line version whereas Paul has filled in a few more details. :-)
It wasn't that I missed the most important step but rather glossed over the
details in the name of brevity. Perhaps I was too brief.

> TC Electronic ... the existence of Freebob convinced them to seek out the
> two people involved in that project and pursue drivers for their new
> chipsets. I was happy to play a tiny role in helping this meeting to take
> place (very tiny).

Ah - I didn't know that.

> The problem with USB2 is that it doesn't seem as though there is any
> similar embedded systems interest in linux support for audio over
> USB2, and nor is there a single company (or 2 companies) with a choke
> hold on the chipsets used for this. This makes the problem a lot
> harder to solve. Maybe the companies that were thinking about firewire
> audio are now thinking about USB2 audio, but if they are I don't have
> my ear close enough to the ground to hear.

For devices with higher channel counts USB2 hasn't really been the interface
of choice thus far. This is mainly due to the limitations of the USB bus
and the fact that it makes it hard to do low latency audio well. Things
like it being a half-duplex bus with a host-slave architecture, and the fact
that the real-world throughput is *much* less than the 480 Mbps *signalling*
rate. The picture is a little different with USB3 since this version adds
full duplex capability along with a number of other enhancements (beyond the
obvious speed increase). How well it will go with audio given the latency
requirements remains to be seen.

As a side note, it seems RME are posed to release a USB2 version of the
Fireface. I don't know much about it except that the device runs different
firmware based on the operating system it's being used with. This suggests
to me that RME work at a very low level both in the operating system driver
stack and at the bus hardware levels in an attempt to circumvent the biggest
audio-related USB showstopper issues.

Regards
  jonathan
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Received on Fri Jul 10 08:15:02 2009