[mythtv-users] MythMusic and only 2 audio channels - no surround?

Thu Mar 31 16:14:48 UTC 2005

David myth-at-dgreaves.com |Lists| wrote:
> Check to see if alsamixer has got a '3D' or 'duplicate front' switch set
> 
> I doubt it's mythmusic - it'll (probably) just send the stereo signal to 
> the pcm channel.
> 
> Also, another option, on my setup it all goes from the pc (via spdif) to 
> an external hi-fi surround processor and I have to turn the pro-logic 
> setting off on the processor to prevent it from trying to decode the 
> stereo into 'surround sound'.
> 
> what hardware setup do you have (ie soundcard -> amplifiers)

I'm using a Sound Blaster Audigy2 and Alsa on a Creative Labs Gigaworks 
750 7.1 speaker system.

I've tried configuring Xine and mplayer to just send out 2.0 stereo (an 
mp3 music file), and yes, the sound comes out of all speakers, not just 
the front ones. Now I don't know where the upmixing is done.

If I set the ALSA 'Center' and 'Surround' settings to 0 with:
amixer set Center 0
amixer set Surround 0
, the sound only comes from the two front speakers. But then that is 
true regardless of whether the source is 2.0 or 5.1. :-(

So it seems 2.0 stereo is upmixed to 5.1 in or before ALSA.. But where?

Isn't this a good diagram:

MPlayer \    --------   ---------------   --------------   --------
          +---| Alsa |---| snd-emu10k1 |---| Audigy2 HW |---|GW 750|
Xine    /    --------   ---------------   --------------   --------

Since I can adjust the center and rear speaker volumes in alsamixer, and 
it then works/applies for both xine and mplayer, then my guess is that 
the upmixing is taking place in ALSA, right? Or is that done in both 
MPlayer and Xine? If its taking place in ALSA, how do I disable it?

<minor_question>
Where do I find any documentation for what the different controls 
actually precisely mean? Such as 'LFE', 'PCM' etc? Anyway, the '3D 
Control - Switch' is off. And what all the alsa.conf settings mean?
</minor_question>

Here is the modules.conf section from alsaconf and the output from `amixer`:

# --- BEGIN: Generated by ALSACONF, do not edit. ---
# --- ALSACONF verion 1.0.0rc2 ---
alias char-major-116 snd
alias char-major-14 soundcore
alias sound-service-0-0 snd-mixer-oss
alias sound-service-0-1 snd-seq-oss
alias sound-service-0-3 snd-pcm-oss
alias sound-service-0-8 snd-seq-oss
alias sound-service-0-12 snd-pcm-oss
alias snd-card-0 snd-emu10k1
alias sound-slot-0 snd-emu10k1
# --- END: Generated by ALSACONF, do not edit. ---

amixer output:

Simple mixer control 'Master',0
   Capabilities: pvolume
   Playback channels: Front Left - Front Right
   Limits: Playback 0 - 100
   Front Left: Playback 60 [60%]
   Front Right: Playback 60 [60%]
Simple mixer control 'Tone',0
   Capabilities: pswitch
   Playback channels: Front Left - Front Right
   Mono:
   Front Left: Playback [off]
   Front Right: Playback [off]
Simple mixer control 'Bass',0
   Capabilities: volume
   Playback channels: Front Left - Front Right
   Limits: 0 - 40
   Mono: 20 [50%]
   Front Left:
   Front Right:
Simple mixer control 'Treble',0
   Capabilities: volume
   Playback channels: Front Left - Front Right
   Limits: 0 - 40
   Mono: 20 [50%]
   Front Left:
   Front Right:
Simple mixer control '3D Control - Switch',0
   Capabilities: pswitch pswitch-joined
   Playback channels: Mono
   Mono: Playback [off]
Simple mixer control '3D Control Sigmatel - Depth',0
   Capabilities: volume volume-joined
   Playback channels: Mono
   Limits: 0 - 3
   Mono: 0 [0%]
Simple mixer control 'PCM',0
   Capabilities: pvolume cvolume
   Playback channels: Front Left - Front Right
   Capture channels: Front Left - Front Right
   Limits: Playback 0 - 100 Capture 0 - 100
   Front Left: Playback 48 [48%] Capture 48 [48%]
   Front Right: Playback 48 [48%] Capture 48 [48%]
Simple mixer control 'PCM Center',0
   Capabilities: pvolume pvolume-joined
   Playback channels: Mono
   Limits: Playback 0 - 100
   Mono: Playback 100 [100%]
Simple mixer control 'PCM Front',0
   Capabilities: pvolume
   Playback channels: Front Left - Front Right
   Limits: Playback 0 - 100
   Front Left: Playback 100 [100%]
   Front Right: Playback 100 [100%]
Simple mixer control 'PCM LFE',0
   Capabilities: pvolume pvolume-joined
   Playback channels: Mono
   Limits: Playback 0 - 100
   Mono: Playback 100 [100%]
Simple mixer control 'PCM Surround',0
   Capabilities: pvolume
   Playback channels: Front Left - Front Right
   Limits: Playback 0 - 100
   Front Left: Playback 100 [100%]
   Front Right: Playback 100 [100%]
Simple mixer control 'Surround',0
   Capabilities: pvolume
   Playback channels: Front Left - Front Right
   Limits: Playback 0 - 100
   Front Left: Playback 100 [100%]
   Front Right: Playback 100 [100%]
Simple mixer control 'Center',0
   Capabilities: pvolume pvolume-joined
   Playback channels: Mono
   Limits: Playback 0 - 100
   Mono: Playback 100 [100%]
Simple mixer control 'LFE',0
   Capabilities: pvolume pvolume-joined
   Playback channels: Mono
   Limits: Playback 0 - 100
   Mono: Playback 100 [100%]
Simple mixer control 'Music',0
   Capabilities: pvolume cvolume
   Playback channels: Front Left - Front Right
   Capture channels: Front Left - Front Right
   Limits: Playback 0 - 100 Capture 0 - 100
   Front Left: Playback 100 [100%] Capture 100 [100%]
   Front Right: Playback 100 [100%] Capture 100 [100%]
Simple mixer control 'Line',0
   Capabilities: pvolume pswitch pswitch-joined
   Playback channels: Front Left - Front Right
   Limits: Playback 0 - 31
   Front Left: Playback 0 [0%] [off]
   Front Right: Playback 0 [0%] [off]
Simple mixer control 'Line2',0
   Capabilities: pvolume cvolume
   Playback channels: Front Left - Front Right
   Capture channels: Front Left - Front Right
   Limits: Playback 0 - 100 Capture 0 - 100
   Front Left: Playback 0 [0%] Capture 0 [0%]
   Front Right: Playback 0 [0%] Capture 0 [0%]
Simple mixer control 'CD',0
   Capabilities: pvolume pswitch pswitch-joined
   Playback channels: Front Left - Front Right
   Limits: Playback 0 - 31
   Front Left: Playback 0 [0%] [off]
   Front Right: Playback 0 [0%] [off]
Simple mixer control 'Mic',0
   Capabilities: pvolume cvolume
   Playback channels: Front Left - Front Right
   Capture channels: Front Left - Front Right
   Limits: Playback 0 - 100 Capture 0 - 100
   Front Left: Playback 0 [0%] Capture 0 [0%]
   Front Right: Playback 0 [0%] Capture 0 [0%]
Simple mixer control 'Mic Boost (+20dB)',0
   Capabilities: pswitch pswitch-joined
   Playback channels: Mono
   Mono: Playback [off]
Simple mixer control 'Phone',0
   Capabilities: pvolume pvolume-joined pswitch pswitch-joined
   Playback channels: Mono
   Limits: Playback 0 - 31
   Mono: Playback 0 [0%] [off]
Simple mixer control 'IEC958 Optical',0
   Capabilities: pvolume cvolume
   Playback channels: Front Left - Front Right
   Capture channels: Front Left - Front Right
   Limits: Playback 0 - 100 Capture 0 - 100
   Front Left: Playback 0 [0%] Capture 0 [0%]
   Front Right: Playback 0 [0%] Capture 0 [0%]
Simple mixer control 'IEC958 Optical Raw',0
   Capabilities: pswitch
   Playback channels: Front Left - Front Right
   Front Left: Playback [off]
   Front Right: Playback [off]
Simple mixer control 'PC Speaker',0
   Capabilities: pvolume pvolume-joined pswitch pswitch-joined
   Playback channels: Mono
   Limits: Playback 0 - 15
   Mono: Playback 0 [0%] [off]
Simple mixer control 'Aux',0
   Capabilities: pvolume pswitch pswitch-joined
   Playback channels: Front Left - Front Right
   Limits: Playback 0 - 31
   Front Left: Playback 0 [0%] [off]
   Front Right: Playback 0 [0%] [off]
Simple mixer control 'Aux2',0
   Capabilities: pvolume cvolume
   Playback channels: Front Left - Front Right
   Capture channels: Front Left - Front Right
   Limits: Playback 0 - 100 Capture 0 - 100
   Front Left: Playback 0 [0%] Capture 0 [0%]
   Front Right: Playback 0 [0%] Capture 0 [0%]
Simple mixer control 'Analog Mix',0
   Capabilities: pvolume cvolume
   Playback channels: Front Left - Front Right
   Capture channels: Front Left - Front Right
   Limits: Playback 0 - 100 Capture 0 - 100
   Front Left: Playback 0 [0%] Capture 0 [0%]
   Front Right: Playback 0 [0%] Capture 0 [0%]
Simple mixer control 'Audigy Analog/Digital Output Jack',0
   Capabilities: pswitch pswitch-joined
   Playback channels: Mono
   Mono: Playback [on]
Simple mixer control 'Audigy CD',0
   Capabilities: pvolume cvolume
   Playback channels: Front Left - Front Right
   Capture channels: Front Left - Front Right
   Limits: Playback 0 - 100 Capture 0 - 100
   Front Left: Playback 0 [0%] Capture 0 [0%]
   Front Right: Playback 0 [0%] Capture 0 [0%]
Simple mixer control 'External Amplifier Power Down',0
   Capabilities: pswitch pswitch-joined
   Playback channels: Mono
   Mono: Playback [off]
Simple mixer control 'Front',0
   Capabilities: pvolume
   Playback channels: Front Left - Front Right
   Limits: Playback 0 - 100
   Front Left: Playback 100 [100%]
   Front Right: Playback 100 [100%]
Simple mixer control 'Sigmatel 4-Speaker Stereo',0
   Capabilities: pswitch pswitch-joined
   Playback channels: Mono
   Mono: Playback [off]
Simple mixer control 'Sigmatel Surround Phase Inversion Playback ',0
   Capabilities: pswitch pswitch-joined
   Playback channels: Mono
   Mono: Playback [off]

-- 
Peter Valdemar Mørch
http://www..........