LibreElec 10 - No USB Audio from Mbox2 Device on RPI4

1st Official Post

    Hi

    After installing LibreElec 10 my Mbox2 audio device wasn't listed in the available audio output devices. So I edited /etc/modprobe.d/alsa-base.conf and modified

    options snd-usb-audio index=0

    to

    options snd-usb-audio index=4

    The device is now listed but sound only outputs via HDMI. The device works flawlessly on my other Raspberry Pi 4 with no configuration necessary.

    Has anyone got any advice?

    Thanks in advance

    Kev

    • Official Post

    Do you use RPi OS on the working device?

    Can you name the used audio driver(s) of the working device?

    LE provides the default ASIO driver, but it seems like your audio interface is using a custom ASIO driver from Digidesign.

    Hi, thanks for the reply

    I just checked. When the Mbox2 is under RPI OS I get sound output but is only configurable by the controls on the box itself. The desktop volume control is greyed out.

    alsamixer states "This sound device does not have any controls"

    I get the same under LibreElec but without any sound. I find audio on Linux to be a bit of a black art. How do I find which audio driver is in use?

    LibreELEC:~ # aplay --list-devices

    **** List of PLAYBACK Hardware Devices ****

    card 0: vc4hdmi0 [vc4-hdmi-0], device 0: MAI PCM i2s-hifi-0 [MAI PCM i2s-hifi-0]

    Subdevices: 1/1

    Subdevice #0: subdevice #0

    card 1: vc4hdmi1 [vc4-hdmi-1], device 0: MAI PCM i2s-hifi-0 [MAI PCM i2s-hifi-0]

    Subdevices: 0/1

    Subdevice #0: subdevice #0

    card 2: Headphones [bcm2835 Headphones], device 0: bcm2835 Headphones [bcm2835 Headphones]

    Subdevices: 8/8

    Subdevice #0: subdevice #0

    Subdevice #1: subdevice #1

    Subdevice #2: subdevice #2

    Subdevice #3: subdevice #3

    Subdevice #4: subdevice #4

    Subdevice #5: subdevice #5

    Subdevice #6: subdevice #6

    Subdevice #7: subdevice #7

    card 4: M2 [Mbox 2], device 0: USB Audio [USB Audio]

    Subdevices: 1/1

    Subdevice #0: subdevice #0

    Edited once, last by evilcraftknife: More Information (September 11, 2021 at 4:46 PM).

    • Official Post

    Then it's a driver issue on both devices. Linux driver support is incomplete. It seems like both systems have trouble to create a virtual mixer device, which controls the volume. Probably LE loads the same drivers, but doesn't accept main audio without such mixer.

    Because drivers are part of the Linux kernel, we can't do anything. If you have another audio interface (default ASIO), try it. Or buy a HiFiBerry DAC. They are supported by LE.

    Oddly I have an x86 based notebook, when I hook the device up to that I get the same output from alsamixer but can still control the audio from the desktop.

    Thanks for the help but I think I'll give up with the Mbox2. Can you recommend an external audio device for LibreElec? Is there a HCL?