HDMI To Optical Stereo

[Fitzcaraldo215]

Yup, that is also a possibility.

 

[Wombat]

Like you, I think the outlet grounds on different power circuits are at fault. Rather than spinning wheels trying some cheap device that may or not work, and which might compromise sound quality, I would simply run a room to room extension cord, plugging both systems into the same electrical circuit.

If it works, unplug and roll it up when not in use. Eventually, do the necessary adjustments at your main circuit box with your now proven concept.

This happened to me between my PC in the neighboring room to my USB DAC, which was on a different power circuit. The extension cord fixed it, and it now runs through a hole in the wall.

The two outlets are in different rooms but on the 'same' circuit. Running all equipment on one outlet would be part of the troubleshooting process and is likely to eliminate the hum but the earthing problem remains on one or both outlets.

 

[RayDunzl]

earthing problem

What's the problem?

 

[Wombat]

What's the problem?

Yet to be located.

https://en.wikipedia.org/wiki/Ground_loop_(electricity)

http://web.mit.edu/jhawk/tmp/p/EST016_Ground_Loops_handout.pdf

Also in my reference folder:

http://www.rane.com/note151.html

http://www.rane.com/note110.html

http://www.jensen-transformers.com/wp-content/uploads/2014/08/an003.pdf

http://www.rane.com/note166.html

https://www.google.com.au/search?so...4GGHP_enAU723AU724&q=jensen+an-004&gws_rd=ssl

 

[Blumlein 88]

Okay I have some results. They are interesting too. Which means they were unexpected. Oooooooooooh!

First this unit would correctly pass both 44 and 48 khz rates. Surprise. Nothing higher however.

Lenovo laptop fed test signals out via HDMI for the HDMI switcher and via USB to the V-link USB to SPDIF converter.

Toslink fed the input of a Tact RCS2 being used as a straight thru DAC.

That fed RCA outputs into an Antelope Audio Zen Tour ADC. Playback was using Foobar 2K set for WASAPI (push).

First a -60 db 1 khz tone 44.1 khz just to see how the noise floors look. HDMI Switcher in Red and V-link in Green.

Looks okay. The little pips at 14 and 16 khz are idle tones in the DAC and ADC respectively.

Now a near full scale 1 khz tone.

Hmmmm, not so good. The noise floor is raised with the HDMI device, and what looks like jitter maybe. The highest of these extra tones are about - 88db so not audibly obvious. But look at the Vlink we are getting THD+N of .00355%

The J test (11,025 hz tone) is not encouraging either.

Ouch! The HDMI Switcher raises the noise floor over the entire 24 khz bandwidth. The tallest spikes each side are -68 db. The V-link has a couple unwanted low level tones, but otherwise looks pretty clean.

The combined full scale 18+19 khz tone for IMD is not so great for the HDMI switcher either.

Notice the 1 khz difference tone for the HDMI switcher is only -74 db down in level while the Vlink is sporting -109 db.

These look very much like the results from the analog output I tested in the other review. I assumed the analog part of the device was substandard. It appears most of it may be coming from high jitter and other issues in the digital area.

Golden ear as I am, I have noticed no problems using it for movies streamed over a Fire TV stick or from a satellite TV box. I did note when listening to the analog outs it sounded smoothed over and lacking in fine detail. Not nasty or brittle. Maybe that modulated noise floor is the problem. I have not blind tested myself on that. I also did some investigating and found it calms down quite a bit as the signal level drops. It looks pretty clean at -12 db and lower. Which still puzzles me a bit on this being a digital connection.

I by now was hoping there was some poor sample rate conversion going on at 44 khz and maybe 48 khz would look better. The results were so much the same there is no point posting the graphs. The Lenovo is outputting HDMI thru a Display Port converter. It is possible the Lenovo is the source of the apparent high jitter in the HDMI signal. I have no way to test that right now.

Oh, forgot. With either connection 60 hz hum was about -109 to -110 db and a touch of 120 hz above the noise floor at -117 to -118 db. Which is from the DAC itself. Nothing added by the Toslink connection.

 

[amirm]

HDMI carries video with it even when you just use it for audio. The audio is slaved to video. So in all but the best implementations, HDMI adds significant amount of noise and jitter.