[LAU] USB audio interfaces >= 8 channels

Robin Gareus robin at linuxaudio.org
Tue May 15 23:23:54 UTC 2012

On 05/15/2012 08:03 PM, Clemens Ladisch wrote:
> Robin Gareus wrote:
>> I'm about to get a ssh-login to a debian box with a 1818VSL connected.

All right. All systems go.
  `jackd S -d alsa -d hw:1 -p 64 -n2` works great!

that's jackdmp 1.9.9 -- git f82ec715
Linux 3.2.0-2-rt-686-pae #1 SMP PREEMPT RT i686 on an Atom CPU dev-kit
board: Genuine Intel(R) CPU @ 1.00GHz (!) running debian/wheezy
(alsa/libasound 1.0.25-2).

jack_lsp lists 18 inputs and 18 outputs (so SPDIF and analog I/O seem to
work simultaneously, but I have not tested SPDIF I/O -- Brian was kind
enough to patch analog output channels 1-8 to their respective inputs
for me to runs some tests.)

`mplayer | patch-cables | jack_capture -c 8` works fine and
`jack_capture -c 18` does too, but the additional 10 channels are of
course silent.

`jack_delay` measured round-trip latency:
        286.903 frames    5.977 ms
        286.540 frames    5.970 ms
        292.858 frames    6.101 ms
        292.902 frames    6.102 ms
        291.903 frames    6.081 ms
        291.903 frames    6.081 ms
        291.903 frames    6.081 ms
        286.898 frames    5.977 ms
        288.124 frames    6.003 ms

Despite the slow system there were no x-runs. CPU utilization was around

As for device configuration:

jackd starts with either -r 48000, -r 44100, -r 96000 and -r 88200. The
1818VSL switches the sample-rate automatically. very neat! See attached
`cat /proc/asound/VSL/stream0`.

The clock-sources can be queried and set using `amixer` or `alsamixer`.
The labels are somewhat misleading but that does not really matter: In
`amixer` all names start with "AudioBox 1818 VSL Clock Selector" - even
the Volume controls (but those end in "Playback V" and "Capture Vo").
`alsamixer` labels them "Front*2, Rear*2, Center, Woofer, Side*2, N/N*1,
and then repeats that for 9 more channels (while in fact it's 8 analog +
2 SPDIF + 8 ADAT -- not sure about SPDIF/ADAT order), but that's just
/usr/share/alsa/pcm/* trying to be smart.

With -r96000 the device only worked with -p256 -n2 or larger periods -
due to CPU limitation (-r 96000 -p128 or -p64 maxed out this weak CPU)
  `jackd -S -d alsa -d hw:1 -p 256 -n2 -r 96000`
measured round-trip latency: 887.173 frames ~ 9.241 ms -- not bad!
..but I'll happily stick with 48k.

FWIW. the device also runs fine with -p 32 !!
  `jackd -S -d alsa -d hw:1 -p 32 -n2`

jack_capture recorded merrily w/o xruns, but jack_delay maxed out the
CPU and caused xruns on this dev-board.

Many thanks to Brian Quandt for making these tests possible.

> Please show the output of "lsusb -v" for this device.

attached. since this ML limits emails to 30K, files are bziped:

#lsusb -v
#amixer -c 1 contents
#amixer -c 1 controls
#cat /proc/asound/VSL/stream0 while running at 44.1 and 48k

I'm going to order one now :)
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