FAQ049
From the ALSA wiki
| The FAQs have been reorganized. The new location of this question is Sound Blaster Extigy (Howto) |
How do I get AC3 surround sound with my Sound Blaster Extigy?
In order to play a DVD with surround sound using your Extigy, you need to access the third device on the card. So if you usually access your Extigy as hw:1 then the third device on the card is hw:1,2, or if you want to use names hw:Extigy,2. This device accepts an SPDIF formatted AC3 stream which your video player passes to the card. Both xine and mplayer can do this.
Xine:
You need to set the passthrough device (device.alsa_passthrough_device) to this device (hw:Extigy,2) and set the speaker arrangement (output.speaker_arrangement) to "Pass Through". N.B. in kaffeine device.alsa_passthrough_device and device.alsa_surround51_device share the same description "device used for 5.1-channel output" so make sure you get the right one.
Mplayer:
The flag -ac hwac3 instructs mplayer to send the encoded stream directly to your soundcard. Ensure that mplayer uses the third device either through a configuration file or at the command line (e.g. playing a dvd: mplayer dvd://1 -ac hwac3 -ao alsa:device=hw=Extigy.2).
Now, whenever you play a video with an AC3 audio track (such as a dvd), the Digital LED will light up and you get surround sound.
Finally you need to adjust the output of the Extigy to your surround sound setup. In alsamixer you can do this by adjusting the "channel routing mode" control to the appropriate setting for your surround configuration. The exaudio driver for OSS mentioned this by the following:
The extigy has seven speaker modes when decoding AC3 audio: mode Rs Ls LFE C R L --------------------- 1 0 0 0 0 1 1 2 0 0 0 0 1 1 3 0 0 1 0 1 1 4 1 1 0 0 1 1 5 1 1 1 0 1 1 6 1 1 0 1 1 1 7 1 1 1 1 1 1 Channel names: Rs = Right surround, Ls = Left surround, LFE = Low frequency enhancement, C = Center front, R = Right front, L = Left front
In alsamixer, 1 corresponds to 00 and 7 to 100 with the rest spaced evenly in between. For a configuration of 2 front and 2 rear speakers, use mode 4. However, a further peculiarity is that the names of the channels as reported by amixer are incorrect, at least in one case. Amixer reports the following:
Simple mixer control 'Master',0 Capabilities: pvolume pswitch pswitch-joined Playback channels: Front Left - Front Right - Rear Left - Rear Right - Front Center - Woofer Limits: Playback 0 - 200 Mono: Front Left: Playback 180 [90%] [on] Front Right: Playback 180 [90%] [on] Rear Left: Playback 0 [0%] [on] Rear Right: Playback 0 [0%] [on] Front Center: Playback 200 [100%] [on] Woofer: Playback 200 [100%] [on]
However, the reported channels do not match the ones that they control (this has been reported as a bug). The mapping is like this:
control: speaker: front left front left front right front right rear left front center rear right woofer front center rear left woofer rear right
In alsamixer you control front and rear with the first two stereo mixers which then gives you front left + right on the first mixer and center and woofer on the second stereo mixer. The other two mono mixers intended for center and woofer give you rear left and rear right.
Additionally there is another mono mixer in alsamixer called Master 1. This mixer controls all channels. Unfortunately it does not increase or decrease them relative to each other but sets them to one fixed value.
