White Noise Through SPDIF When No Audio Playing

Sylvester Ink · 11-21-2012, 12:05 PM

I have an Asus Xonar STX soundcard, outputting sound through an SPDIF connection to an external DAC. When I'm not playing back any audio, I get hissing, white noise. When I play back any sort of audio, everything is perfect.

From what I gather, the issue may be that the DAC isn't receiving any signal from the soundcard until something is played, in which case it works just fine. Is there any way to fix this issue?

unclejed613 · 11-21-2012, 08:29 PM

is this optical or coax for the connection. if it's coax, what type of cable is it? a cheap coax cable (with far too much capacitance) may be rounding off the pulse edges, which could show up as jitter at the input to the dac. a cable made for video will have better pulse characteristics.

Sylvester Ink · 11-21-2012, 11:09 PM

I tried it with both optical and coaxial. Both are excellent quality cables. The issue does not occur on Windows, only on Linux.

cheese1343 · 11-22-2012, 03:02 AM

If you have a microphone connected, try muting it.

Sylvester Ink · 11-22-2012, 01:19 PM

It's muted. (Used alsamixer to do so. In fact, I tested pretty much everything in alsamixer.)
After testing another DAC, I've confirmed that it's not receiving any sort of signal when not playing, which is likely what's causing the problem. From reading around, I've seen people mention that it may be caused by APCI settings for saving power, or incorrect PCM settings or something like that.