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

[rastus]

Hey, re HDMI issue.... could this be something to do with CEC via HDMI? Isn't the latest version of RuneAudio sending a signal to the TV? I know since installing the latest version of RuneAudio that when I turn my Pi on, with HDMI cable attached, because I also use it for watching movies (OpenELEC) that the TV comes on when the Pi is turned on. I will have to test this, run the Pi with no HDMI cable attached, see if it sounds any better.

[PeteB]

At least one of the two monitors I tried was definitely not CEC compatible, so this would not be the main cause. A TV can turn itself on when it detects a signal on the HDMI port, or switch its input to that port, without complete CEC compatibility.

My knowledge of HDMI is pretty limited. I am just a plain old EE, and to understand HDMI fully, I believe only a degree from Hogwarts will do...

I have now been told the HDMI implementation at the Pi end cut some corners in the interest of affordability, with the assumption that the Pi would not be connected to another ground, but float on its isolated wall wart supply (yes, we are back to the supply). When we connect the DAC+ RCA cables to a power amp, there is a potential problem. I can't find a schematic to confirm.

In my case, when I connect the output of the DAC+ to the USB sound card, and from there to the PC USB port, and to the charger, and a a wall socket, a ground loop is created. I will test for this by end of this weekend. (still looking at your links about network software, too).

[rastus]

...I believe only a degree from Hogwarts will do...
...yes, we are back to the supply...

LoL @ Hogwarts (damn you Harry Potter). I used a Behringer U-CONTROL UCA202 for a while... used USB from the Pi for sound signal to the Behringer (powered via the USB from the Pi), out from the Behringer's (RCA or optical) to my AVR. No need in that case for a wall-wart attached to the Behringer to power it. Anyway, sounded good, just was limited to 96kHz (or maybe 48kHz, can't think right now). Anyway, I may have already posted this (if so, then ignore it)...

Don't know if this is still relevant, I started reading this post from the beginning and....

The Pi has two LEDs, one red and one yellow/green.... my PiFi DAC has two LEDs, one red and one yellow/green. When connected and powered on (and enabled in RuneAudio) the DAC's LEDs both come on, both red and one yellow/green. If I use OpenELEC (with the DAC not enabled), the DAC's red LED comes on, but the yellow/green LEDs do not come on. Either way, with RuneAudio or OpenELEC, the Pi's yellow/green LED seems to only come on when the CPU is doing processing. Thus, when shutting down the Pi, I look for the yellow/green on the Pi itself... when the blinking yellow/green stops, then I turn the power supply off... and all LEDs go dark. I turn the power off to the Pi because I'm using a battery pack, every little bit hurts (uses up power, no matter how small the amount). Also, I have a USB cable with a switch installed in the length of the cable itself. Like so (http://www.geekroo.com.au/)....

[PeteB]

Well, it is not the power supply, at least not the stock Pi 2 supply or either one of the other two I tested with. At least not the supply for the Pi. The Pi p/s makes a very small contribution to the noise, almost not measurable (with what I have to work with).

I did a lot of testing over the weekend, and I am still looking over the results.

Tentatively I think I have a combination of a ground loop, and some additional noise, but I cannot sort it out because as potential noise sources are disconnected, this also breaks the ground loop (if any). If I feel there is a conclusive result, I will post more, in the meantime I have a lot of numbers to crunch (sigh).

[rastus]

Well, it is not the power supply, at least not the stock Pi 2 supply or either one of the other two I tested with. At least not the supply for the Pi. The Pi p/s makes a very small contribution to the noise, almost not measurable (with what I have to work with).

Tentatively I think I have a combination of a ground loop, and some additional noise, but I cannot sort it out because as potential noise sources are disconnected, this also breaks the ground loop (if any). If I feel there is a conclusive result, I will post more, in the meantime I have a lot of numbers to crunch (sigh).

Oh good, so it's a local problem with your setup PeteB? Thank goodness, for a moment there I thought.... well... not so good for you I guess, sorry about that brother. I didn't mean... well I'll just remove my foot from my mouth and move along.

PS: Your feedback and dedication to hard work is always appreciated (by me at least) as well you (should) know. I may banter with you... but it's a respectful banter.

PSS: Don't 'feed' me, LoL!

[PeteB]

...so it's a local problem with your setup PeteB? ...

Not quite. I have some kind of local problem, yes, BUT - the HDMI is like an open back door to let the dogs in...

Here is how:

Normally, the Pi is isolated at its power supply (floating). The only connection is from the DAC or DIGI to the stereo gear. This is the "good" configuration.

Once you plug in the HDMI cable (or ethernet) this stops being "good" and opens the possibility for noise, ground loops, and other issues, just like an open back door. With a small touchscreen powered by the same isolated supply as the Pi, it is not as noticable. As more people start using the local browser connected to a conventional TV set or HDMI monitor, it will be more common.

To put it in perspective, what I measured reduces the useful audio range to about 14~15 bits, and then it is cut down more if volume control is used in RuneAudio.

In the worst case, you start with 24-bits, and end up with FM-quality sound...

[PeteB]

I am calling this "solved" because it is not a RuneAudio problem, and because I think I am posting about issues with HDMI, noise, and audio that have been documented and well covered in other places.

Using a DIGI+ with transformer isolation fixes the problem. Carefully removing or isolating noise sources reduces the noise close to un-measurable.

[urchin.us]

Better late than never....As stated above the problem is likely related to something called a 'Ground Loop', simply use a ground lift adapter on your monitor power cable, or you can actually just pull the monitor ground cable pin on the power cable (Not recommended....but this how I fixed the problem on my end).


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