View Full Version : [ubuntu] No 5.1 with optical connection

May 29th, 2011, 10:14 AM
I have a Realtek HD audio chipset on my motherboard, which connects to my 5.1 speaker system through and optical connection to my AV Receiver/Amp!

I can only get stereo working in the audio options... selecting analogue 5.1 results in no sound (makes sense as the connection is digital)

Question is, how can i get full 5.1 working with an optical out??

May 29th, 2011, 11:40 AM
Optical audio output is the Toslink interconnection of S/PDIF.

S/PDIF supports stereo PCM commonly only up to 96KHz/20bit or AC3 (A52 dolby dig) or DTS.
It can possibly support 2 ch 192KHz/24bit but most consumer equip will not.

Multi-channel audio can only be sent over S/PDIF by AC3 or DTS.
AC3 is always matrix encoded, DTS can be non-matrix encoded but it almost always is not...
AC3 max 640Kbps DTS max 1.5 Mbps ?

If you want to output HD audio (digital) you need to use HDMI or special interconnect to external DACs (I2S).
The HDMI connection requires the video driver to provide/present the audio device to alsa driver.

Default system wide audio:
To output AC3 or DT3 5.1 over S/PDIF select the output device "Digital Stereo (IEC958)"
From cmdline:
vlc --aout alsa --alsa-audio-device iec958