Installation of a C-Media based soundcard on Debian GNU/Linux

Last year I bought a new Dolby Digtal/DTS A/V-receiver (Denon AVR-1802). The output power was incredible but I wasn't happy with the sound quality. So I've decided to replace the analog connection between my computer and the amplifier with an optical cable. The AVR-1802 provides a coaxial connector (gilt) and a S/PDIF (optical) port. So I was in need of a soundcard which has such connector. All my colleagues swear on Creative Labs cards but I wouldn't go with the mainstream. After a few days of search I encountered a very cheap card from the german distributor Pearl [0]:

Zoltrix [1] Nightingale Pro 6

• 6 channels (5.1/AC3)
• 16 Bit DAC
• C-Media 8738-6CH sound chip
• S/PDIF input/output
• digital coaxial input/ouput (gilt)
• General MIDI 128 Sounds
• Signal to Noise Ratio > 90dB
• Dolby Digital/DTS/Pro Logic II pass through
• linux drivers (shipped with standard linux kernel)
• very cheap: at the moment about €40

The first goal was to get some noise out of the speakers :) To achive this we need support for the C-Media chip in the kernel (module/build in):

<*>   C-Media PCI (CMI8338/8738)
[*]   Support CMI8738 based audio cards
(2)   Number of speakers 2, 4, 5, 6

Number of speakers should be 2 because we do not want to use the onboard AC3-decoder. If you say 6 here you'll not be able to use line-in, line-out and mic-in because they're used as connectors for active front/rear/center-speakers. After reboot it should be possible to play mp3 music via aRts or OSS. Also the S/PDIF port is expected to work.

The second goal was Dolby Digital and DTS support to enjoy DVD's. xine has a problem with ioctl's. This problem exposes by not activating the digital out while playing. You still can use xine's aRts plugin for sound support but aRts cannot pass through the AC3 signal and so you've only 2.0 stereo (PCM). A small tool called cmictl [2] depicts a kluge. With cmictl it's possible to manually switch on S/PDIF input, output and frequency:

cmictl -o ON -i ON -8 ON

This command activates S/PDIF input and output and collimated frequency to 48 kHz. A few tweaks in ~/.xine/config are needed to pass through the AC3 stream to the ampilifier:

audio.driver:oss
audio.a52_pass_through:1
audio.five_lfe_channel:1
codec.a52_level:100
codec.a52_dynrng:0
codec.a52_surround_downmix:0
audio.resample_mode:off
audio.force_rate:48000

Now it should be feasible to enjoy movies with Dolby Digital Surround Sound and DTS. I really recommend you an active subwoofer :) The next few pics show components of my sound system:

Sherwood SP-310W subwoofer (80 watt sinus)
Subwoofer (rear view)
Denon AVR-1802 A/V-Receiver (5x115 Watt sinus)
Infinity center speaker/DVD-player
Soundcard Zoltrix Nightingale Pro 6

References