[mythtv-users] Is 5.1 surround sound possible with a Sound Blaster Extigy USB from Creative Labs ?

[Greg Tippitt]

Is it possible with ALSA to get 5.1 surround sound with the Extigy with
either analog or AC3 hardware decoding? I have been unable to get 5.1
surround sound to work with the system I have set up for MythTV. I can get
stereo music, DVD, and TV in quality ranging from excellent to barely
recognizable, but only in 2 channels. I've tried all of the versions of the
".asoundrc" file I can find and rechecked my ALSAMIXER settings. I know that
the Extigy hardware works great in standalone mode.

I've been using the Extigy for a few years in standalone mode to decode
digital output from a DVD player (spdif coax) and DirecTV-TIVO series II
(via TOSLINK). I have it connected to my old analog amplifier that has
discrete 5.1 analog inputs, but no digital inputs. While in standalone mode,
the Extigy will decode AC3 streams from either input and upmix stereo to 5.1
when needed. When the Extigy is connected to the MythBuntu system, I can
only get stereo. I get the same results from MPLAYER, MythTV, and VLC.

I have a fresh install of MythBuntu 11.04 that I'm trying to finish setting
up. I've had no problems configuring my 2 ASTC tuners, an OnAir Sasem USB
and a Hauppauge WinTV-HVR-1800 PCI-X that are working great. I've had no
problems configuring LIRC to work with a Creative SB0540 USB IR receiver and
Creative RM-900 remote control. I've got a NVIDIA 8500GT PCI-X16 to replace
the motherboard video, which provides S-Video-out for my SD-TV. I also have
a VGA-CRT display connected for administration on the system when using the
keyboard and mouse. This is all installed in an old eMachine t3418 (AMD
Sempron 3400+ / 2.0 GHz) with 1.5 GHz RAM. It is a very eclectic assortment
of hardware I've collected cheaply from yard sale parts and stuff people
have thrown away.

I can get poor quality surround sound from the Realtek (Intel A97
compatible) motherboard sound. I discovered an odd aspect of the motherboard
sound that might help some people. My motherboard has only 3 jacks for
headphone, mic, and line-in, but these will produce 6 channel sound output.
The microphone and line-input jacks are used for output rather than input
when 5.1 surround sound is chosen.

Since I'm not wanting to use both sound devices, I greatly simplified my
configuration of the Extigy by turning off the motherboard sound in CMOS
setup. The "/etc/modprobe.d/alsa-base.conf" file can then be modified to
comment out the "options snd-usb-audio index=-2" line that forces USB sound
devices into the second slot. If the USB sound device is the only sound
device in use, loading the USB sound device as the default simplifies many
configurations issues, so that many applications will work by simply
selecting ALSA as the sound output option.

The EXAUDIO driver for OSS supported compressed 5.1 for AC3. I've tried
compiling the EXAUDIO driver and replacing ALSA with OSS, but it is going to
require me to compile a new kernel, which I've never tried before. If there
is a way to get the Extigy to work with ALSA, I would prefer this to trying
to get the OSS driver working. If anyone can let me know if it possible to
get 5.1 surround sound from the Extigy under ALSA, I would greatly
appreciate the help.

Thanks,

Greg
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