On 3/12/21 3:00 PM, David Runge wrote:
On 2021-03-12 00:08:53 (+0100), Thibaud Keller wrote:
Thanks Roger for the suggestion,
we are actually running at 48k.
These limitations seem to be built in as you can see on page 88 of the
manual
https://www.rme-audio.de/downloads/mface_pro_e.pdf
This might be due the fact, that the class compliant mode is not aimed
at Linux and/or general computing, but there to support iPads (that's at
least the case in the Fireface UFX series).
Ha, interesting... I was actually looking at the usb spec a couple of
days ago (due to this thread) and trying to find a reference to limits
on channel count - a quick browse/search did not find anything but I may
have missed it. Maybe this is in some other document.
I received this fun piece of information from an RME employee at
superbooth two years ago. The channel limitations in class compliant
mode in e.g. the RME Fireface UFX (II, +, etc.) are hardcoded and
matched to the capabilities of some iPad version that was supposed to be
supported back then (and is by now long EOL).
Motu's original firmware for the AVB interfaces was upgraded early on to
be able to do up to 64 channels on usb2 (which I have been using
extensively). It was latter downgraded to just 24. I started a ticket
and was told that they were having (unspecified) problems with it.
There is a hack that makes it possible to connect the linux usb driver
to the proprietary usb endpoints of the audio interface and thus run at
up to 64 channels (for 44.1/48KHz sampling rate, of course). This
involves kernel patches and also manually switching the interface to the
proprietary mode through an hhtp/json command (otherwise it just uses
the class compliant endpoints[*] after you plug it in). This very long
thread has information about this:
https://linuxmusicians.com/viewtopic.php?f=6&t=18046&sid=3deb30fa5d04d5240741640f329aa2ea
(many options explored but no real solution that works all the time)
While the hack makes it possible to use 64 channels on newer hardware
that cannot be downgraded to the older Motu firmware, its behavior is
not 100% reliable - it might be better behaved in 5.11+ but I have not
tried yet.
-- Fernando
[*] I imagine there is some initial handshake that tells the card that
the motu driver is accessing it, and that is obviously missing in linux
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