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Thread: Help understanding alsamixer

  1. #1
    Join Date
    Oct 2010

    Help understanding alsamixer

    I've just got ALSA working on a minimal Ubuntu 10.04 install, but I'm having trouble getting sound to the back speakers. I have an old quadrophonic stereo hooked up to XBMC, which is set for 4.0 output. When I first got the sound working, I had very very quiet sound out of the back, and in trying to boost the volume, I lost it entirely.

    I think the problem is I have no idea what half these channels are. My alsamixer lists:

    Master (obvious)
    Master Mono
    3D Control - Center <--
    3D Control - Depth <-- I have no idea what these are
    3D Control - Switch <--
    PCM <--
    Front (controls my front volume)
    Surround (No effect)
    Center (I don't have a center speaker)
    Center/LFE Exchange
    Mic Boost
    Mic Select
    S/PDIF Output
    S/PDIF Playback
    PC Speaker
    Mono Out
    Alternative Level to Surround Out
    Downmix LFE and Center to Front
    Downmix Surround to Front
    External Amplifier
    Input Source Select (2 of these)
    Smart 5.1 Select

    I can get by with just front audio, but I'd really like to get the rear speakers working before I take the keyboard off.

  2. #2
    Join Date
    Dec 2007

    Re: Help understanding alsamixer

    Got a similar setup (4.0 surround configuration, quad receiver/amp). My motherboard supports discrete outputs, and the rear speakers seem bundled to the 'surround' virtual fader. The motherboard soundcard's analog audio out is a bit noisy, as most are.

    It might be a good idea to get a surround test suite of some sort rolling...I used a Radio Shack optical drive brush/AV configuration disk.

    I typically use VLC for video playback, and with surround decoding enabled (not AUTO), it works out of the box. Without AC3 compression, the surround effects might be too quiet to be heard in your environment, depending on source.

    Keep in mind, a lot of older surround schemes (pro logic and whatnot) simply take corresponding front channels, invert the phase, and aim it back at the main speakers with delay. Unless you are sure you are feeding it a proper surround stream, and decoding it properly, results will vary per source.

  3. #3
    Join Date
    Nov 2007
    Austin, TX
    Ubuntu 8.10 Intrepid Ibex

    Re: Help understanding alsamixer

    How is the stereo hooked up? (ie. 3.5mm, spdif...) Someone correct me if I'm wrong, but PCM is a pretty important channel to have turned up. Also, have you swapped the speakers out for something else, say powered desktop speakers... That way you can rule out a config issue w/ the stereo (although you may know for sure that its the computer, just thought I'd suggest it)


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