I was trying to get a picture of how good/bad HDMI for audio is, compared to toslink and internal (UPnP) playback.
The test setup:
Test file (from Focal's tools CD) 1khz sine wave.
Playback from LMS on Raspberry Pi with:
1. Raspberry Pi (Squeezelite player) to Cambridge Audio CXU HDMI input
2. Squeezebox Classic player to Cambridge Audio CXU optical input
3. Internal CXU UPnP client
In each case, I fed the CXU's digital out (optical) into the direct optical in on a Foxconn mini pc (no USB soundcard in the chain), recorded in Audacity via Pulseaudio and then imported into REW. I also had a "Control" of the pcm test file imported directly into REW.
Apart from the very cheap measurement system, I think the biggest potential issue with this test is that the CXU unit might be too good at cleaning up its inputs. Unfortunately, I can't test using my AVR as it has no digital output.
That said, the results surprised me, in that toslink was the outlier: not terrible but noticeably worse than the other 3 which were all very similar. And at very high frequencies the directly imported wav file was slightly noisier.
But based on this evidence, the Pi's HDMI seems "good enough" for music playback.
Here's the graph (toslink is blue) and the REW files (separate due to forum size limitations):
The test setup:
Test file (from Focal's tools CD) 1khz sine wave.
Playback from LMS on Raspberry Pi with:
1. Raspberry Pi (Squeezelite player) to Cambridge Audio CXU HDMI input
2. Squeezebox Classic player to Cambridge Audio CXU optical input
3. Internal CXU UPnP client
In each case, I fed the CXU's digital out (optical) into the direct optical in on a Foxconn mini pc (no USB soundcard in the chain), recorded in Audacity via Pulseaudio and then imported into REW. I also had a "Control" of the pcm test file imported directly into REW.
Apart from the very cheap measurement system, I think the biggest potential issue with this test is that the CXU unit might be too good at cleaning up its inputs. Unfortunately, I can't test using my AVR as it has no digital output.
That said, the results surprised me, in that toslink was the outlier: not terrible but noticeably worse than the other 3 which were all very similar. And at very high frequencies the directly imported wav file was slightly noisier.
But based on this evidence, the Pi's HDMI seems "good enough" for music playback.
Here's the graph (toslink is blue) and the REW files (separate due to forum size limitations):