knillenhower wrote:recently i was looking for an USB audio interface for stereo output and mic input. the Motu M2 attracted my attention. on (non-linux) tests low latency and high quality preamps are reported and it possesses a LCD level meter (which is quite unique for this device class). a popular competitor in this class is the focusrite scarlett 2i2, but i heard on linux there are issues with the latest 2i2 generation (gen 3).
very quickly i tested the Motu M2 on an old debian machine (debian 9/stretch+linux 4.9+xfce) without success.
maybe i install jack in the future and take a deeper look on latency. if so i can give an update here.
Thank you for posting this. I also bought an M2 with intention to use it with Linux, mainly for playback from a Raspberry Pi streamer, but also for some recording projects, digitising old LPs and cassettes. As you say, there is little information anywhere on how to make this work, so perhaps this forum could be a place to share experiences.
My standard desktop is Linux Mint 19.3, so Debian-Buster/Sid based.
Kernel: 5.0.0-37-generic x86_64
alsa-base 1.0.25+dfsg-0ubuntu5
alsa-utils 1.1.3-1ubuntu1
Plugged in the M2 and a new card appears as expected.
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$ aplay -l
...
card 2: M2 [M2], device 0: USB Audio [USB Audio]
Subdevices: 1/1
Subdevice #0: subdevice #0
and lots of new PCMs:
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$ aplay -L
...
sysdefault:CARD=M2
M2, USB Audio
Default Audio Device
front:CARD=M2,DEV=0
M2, USB Audio
Front speakers
surround21:CARD=M2,DEV=0
M2, USB Audio
2.1 Surround output to Front and Subwoofer speakers
surround40:CARD=M2,DEV=0
M2, USB Audio
4.0 Surround output to Front and Rear speakers
surround41:CARD=M2,DEV=0
M2, USB Audio
4.1 Surround output to Front, Rear and Subwoofer speakers
surround50:CARD=M2,DEV=0
M2, USB Audio
5.0 Surround output to Front, Center and Rear speakers
surround51:CARD=M2,DEV=0
M2, USB Audio
5.1 Surround output to Front, Center, Rear and Subwoofer speakers
surround71:CARD=M2,DEV=0
M2, USB Audio
7.1 Surround output to Front, Center, Side, Rear and Woofer speakers
iec958:CARD=M2,DEV=0
M2, USB Audio
IEC958 (S/PDIF) Digital Audio Output
dmix:CARD=M2,DEV=0
M2, USB Audio
Direct sample mixing device
dsnoop:CARD=M2,DEV=0
M2, USB Audio
Direct sample snooping device
hw:CARD=M2,DEV=0
M2, USB Audio
Direct hardware device without any conversions
plughw:CARD=M2,DEV=0
M2, USB Audio
Hardware device with all software conversions
With VLC audio output module set to Pulseaudio, and Audio Device set to M2 Analogue Stereo I can see the volume meters waggling up and down in pavucontrol, but nothing can be heard. Seems like it's muted. I read that ALSA devices often come up muted, and I should use an amixer command to un-mute. Problem is, there isn't a mixer listed on the M2:
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jordan@ximinez /var/log $ amixer -c 2
jordan@ximinez /var/log $
This is perhaps a fundamental reason for the failure to playback. I'll spare you all the other fiddling around I did with alsa. I'm far from an expert, though willing to learn.
So I followed your lead and installed a fresh Arch Linux setup (no small feat, since I've never installed Arch!). Things are a lot more successful there, playback works right away. I haven't spent enough time to get to grips with sample rate and such, but it's a huge step forward. Not sure if it's to do with later versions (not looking at the box now, but it seems like it has kernel 5.4.6 and arch-utils 1.2.1, so well in advance of my Mint/Debian system). My plan is to learn enough about how it's working on Arch to understand what config might be needed to get it running on Debian. Grateful for any hints if anyone has insight.
Rob