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Thread: Problem with pulseaudio showing only 2 input channels

  1. #1
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    Oct 2020
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    Problem with pulseaudio showing only 2 input channels

    Hello everybody,

    i want to use a MixPre-10 II (from Sound Device) to capture multiple microphones (up to 5 or 6) at the same time and analyze the signals on a computer.
    The MixPre-10 II is connected via USB-C to a pc running Ubuntu OS and a python script including pyaudio to capture the multiple channels.

    The problem is that pavucontrol (and Audacity e.g.) only shows 2 input channels.

    The MixPre-10 II is configured correctly, because on a Mac OS every 12 input channels are shown.

    'pacmd list-sources' produces the following output:
    Code:
     * index: 11
        name: <alsa_input.usb-Sound_Devices__LLC_MixPre-10_II_TJ0120085001-00.iec958-stereo>
        driver: <module-alsa-card.c>
        flags: HARDWARE DECIBEL_VOLUME LATENCY DYNAMIC_LATENCY
        state: SUSPENDED
        suspend cause: IDLE 
        priority: 9048
        volume: front-left: 65536 / 100% / 0,00 dB,   front-right: 65536 / 100% / 0,00 dB
                balance 0,00
        base volume: 65536 / 100% / 0,00 dB
        volume steps: 65537
        muted: no
        current latency: 0,00 ms
        max rewind: 0 KiB
        sample spec: s16le 2ch 44100Hz
        channel map: front-left,front-right
                     Stereo
        used by: 0
        linked by: 0
        configured latency: 0,00 ms; range is 0,50 .. 2000,00 ms
        card: 6 <alsa_card.usb-Sound_Devices__LLC_MixPre-10_II_TJ0120085001-00>
        module: 33
        properties:
            alsa.resolution_bits = "16"
            device.api = "alsa"
            device.class = "sound"
            alsa.class = "generic"
            alsa.subclass = "generic-mix"
            alsa.name = "USB Audio"
            alsa.id = "USB Audio"
            alsa.subdevice = "0"
            alsa.subdevice_name = "subdevice #0"
            alsa.device = "0"
            alsa.card = "1"
            alsa.card_name = "MixPre-10 II"
            alsa.long_card_name = "Sound Devices, LLC MixPre-10 II at usb-0000:00:14.0-3, high speed"
            alsa.driver_name = "snd_usb_audio"
            device.bus_path = "pci-0000:00:14.0-usb-0:3:1.0"
            sysfs.path = "/devices/pci0000:00/0000:00:14.0/usb1/1-3/1-3:1.0/sound/card1"
            udev.id = "usb-Sound_Devices__LLC_MixPre-10_II_TJ0120085001-00"
            device.bus = "usb"
            device.vendor.id = "0926"
            device.vendor.name = "Sound Devices, LLC"
            device.product.id = "0210"
            device.product.name = "MixPre-10 II"
            device.serial = "Sound_Devices__LLC_MixPre-10_II_TJ0120085001"
            device.string = "iec958:1"
            device.buffering.buffer_size = "352800"
            device.buffering.fragment_size = "176400"
            device.access_mode = "mmap+timer"
            device.profile.name = "iec958-stereo"
            device.profile.description = "Digital Stereo (IEC958)"
            device.description = "MixPre-10 II Digital Stereo (IEC958)"
            alsa.mixer_name = "USB Mixer"
            alsa.components = "USB0926:0210"
            module-udev-detect.discovered = "1"
            device.icon_name = "audio-card-usb"
        ports:
            iec958-stereo-input: Digital Input (S/PDIF) (priority 0, latency offset 30000 usec, available: unknown)
                properties:
                    
        active port: <iec958-stereo-input>
    If i change the soundcard to MixPre-10 II in alsamixer, the message "This sound device does not have any controls" appears.

    I suspect it has something to do with PulseAudio, but as I have very little experience in this field, I wanted to ask if anyone had a similar problem or has any idea how to face the problem.

    Many thanks in advance!

  2. #2
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    Re: Problem with pulseaudio showing only 2 input channels

    I don't know anything about that unit, but does Audacity recognize it? You need to go to Edit -> Preferences -> Devices -> Recording. That's how I get to our 32 channel mixer.

  3. #3
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    Re: Problem with pulseaudio showing only 2 input channels

    Audacity recognize it, but only 2 channels.

    Does your 32 channel mixer appears as a 32 channel mixer in your system sound settings?

    Edit: Running Ubuntu 18.04.5 if it is important.
    Last edited by sevland2020; October 21st, 2020 at 12:03 PM.

  4. #4
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    Re: Problem with pulseaudio showing only 2 input channels

    Our mixer is an Allen & Heath QU32. In Audacity it comes up as "QU32". Also, while still in Audacity, either in Preferences (where you were previously) or on the main screen, there is a place for you to chose the number of channels. If I am only using the first 15 channels of the mixer, I can just set Audacity to only record 15 channels on the main screen.

  5. #5
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    Re: Problem with pulseaudio showing only 2 input channels

    The problem is that i can only choose between 1 and 2 channel in Audacity because the system itself recognize the device as 2 in / 2 out.

  6. #6
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    Re: Problem with pulseaudio showing only 2 input channels

    And Audacity does recognize the unit correctly?

  7. #7
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    Re: Problem with pulseaudio showing only 2 input channels

    No. Audacity recognize the unit as 2 in / 2 out like ALSA does.

  8. #8
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    Re: Problem with pulseaudio showing only 2 input channels

    But, does Audacity recognize it as a MixPre-10 II? File -> Preferences -> Devices -> Recording. In that box, you should be able to click on it and see all the possibilities. For instance on my 32 channel mixer, when I click on that box I get QU32 32 different ways: 1 channel, 2, channels, 3 channels, 4 channels, etc. all the way up to QU32 32 channels.
    Last edited by Autodave; 4 Weeks Ago at 10:09 PM.

  9. #9
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    Re: Problem with pulseaudio showing only 2 input channels

    Sorry for the late answer.

    Audacity recognize it as a MixPre-10 II, but under File -> Preferences -> Devices -> Recording only 2 channels are available.
    The problem does not lie with audacity, but with ALSA I think.

  10. #10
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    Re: Problem with pulseaudio showing only 2 input channels

    There's a comment at Ardour forums that may or may not be relevant:

    it is necessary to run the MixPre-D in “full-speed” USB mode. To do this, hold down the
    Headphone Controller while inserting the USB plug to the MixPre-D.

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