Noise from HDMI port, Pi2, HiFiBerry DAC+ [SOLVED]

[PeteB]

Edit (6-6-2016): Time to put this to rest...

*****

I've had some issues with noise on the outputs of the DAC+. I was finally able to trace it to noise conducted over the HDMI port when the cable is connected. I would be grateful for any information or links on how to keep this from happening.

With the HDMI cable, I get around 80db in actual use, equivalent to 14-bit useful resolution. Without the cable I get close to the expected 100~110 db dynamic range. I would like to do better.

See below for some screen grabs from RMAA. I also have similar results from another tool called "Daquarta" I can post later.

The DAC+ results are very good, when tested with the HDMI cable unplugged, so I do not suspect a hardware problem.

In the pics, the white trace is a test with HDMI unplugged. The green trace shows the effects of the noise with HDMI connected. The graphs are on a logarithmic scale, so the difference does not look like much, but it is significant.

[dunghnguyen]

I am not fully aware what you have done on the analysis but it looks meaningful for the improvement (if any). For me, I just don't plug the HDMI haha... I love Rune with DAC+ a lot...its sounds are really nice

[hondagx35]

Hi Pete,

is this with a regular monitor or TV plugged in the HDMI?
I'm asking, because with my small TFTs (waveshare, ODROID) i can't measure any noise.

Frank

[PeteB]

@dungnguyen: I have recorded amazingly good results with the DAC+, when under ideal conditions, and when testing at 44.1K, 48K, 96K (I have nothing that will reliably measure above that). Unfortunately, there is this noise susceptibility, which can sometimes make the test results much worse.

@Frank: I do not own any small TFTs. In this test I used an LCD TV. Other tests with a new-ish Viewsonic HDMI LED monitor were similar. I believe the HDMI is conducting noise from other sources (note the peak at 60Hz - well, 50Hz in your case). The TV/monitor is only a small contributor to the noise. This can be shown by leaving the TV connected to power and to the HDMI port, and disconnecting or turning off everything else.

[dunghnguyen]

@PeteB: thanks for your analysis as well as advice. For my ear, I cannot recognize any noise with or without hdmi port connected. Thanks God for that so that I can still listen DAC+ ...I luv it much ...play from Pi 2 signal out via USB to DAC SMSL M8 decoded perfectly.

[rikardo1979]

always use good quality cables All this is comming from your cable as its like an long aerial

[PeteB]

[PeteB]

Test with an external USB 24-bit soundcard, and software calibrated to the sound card inputs:



Test conditions:
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test signal: 984.350Hz, 48KHz-16 bit wav file, 50% FS, 1.01Vrms measured at the DAC+ output
source: RuneAudio, HW volume control (or disabled) at 100, HiFiBerry DAC+ I2S
input: SB X-Fi HD, ~12k-ohm impedance, 96K-24bit resolution
software: Daquarta for Windows v9.10, calibrated to sound card inputs at 1V rms

Disclaimer: Everything was adjusted to give the best results. Distortion and noise would be higher in normal use, with normal recorded music, and at normal listening volumes.

@Rikardo: Same interconnect cables used for this test, except HDMI cable NOT plugged, and a shorter better quality RCA cable (still under $10... )

@dunghnguyen: If you keep noise sources away from your Pi, and use your battery bank with no connections to the mains except your power amp, you should be able to come close to the same low noise and THD.

[rikardo1979]

[PeteB]