(07-11-2022, 07:42 PM)Reddo84 Wrote: So I've disconnected the USBridge Sig from my system completely and pieced it back in - bit by bit - checking for distortions after each step (after rebooting). For a DAC, I used a Dragonfly Red instead of my regular miniDSP 2x4 HD. Everything went fine, no distortions.
It's a fact of life that digital computers generate prodigious amounts of digital noise.[1] Circuit designers try to minimize the impact of this noise (in order to meet regulatory requirements if nothing else) but it can leak across various parts of the system (aka EMI or, crudely, "cross talk"). The Allo claim is that the USB port on its USBridge is especially "quiet" in this regard. It certainly seems there's not enough leakage to affect the Dragonfly, but then I haven't had this problem with any regular RPi and several different USB DACs either.
Quote:The last thing I changed back to normal was the DAC ... et voilá: With the miniDSP 2x4 HD, the distortions are back full force when not in CoverView. When in CoverView, everything is fine.
OK, so this suggests there is leakage to the miniDSP which is causing havoc. The input circuitry to the Dragonfly and the miniDSP differs and the internal processing of the reconstructed digital signals differs so I can't comment on why this is occurring.
The hard bit is knowing how the leakage is occurring so it can be mitigated. Could be through poor electrical grounding, poor power supply filtering, poor cable shielding, yada yada yada. One could write a book about this. Indeed, many such books have already been written. There are all sorts of tricks to EMI mitigation but I have no idea which trick(s) will apply in your case.
Quote:Another observation: When I boot up the USBridge Sig and only then connect the screens HDMI cable to the device, the resolution is off (too low), but there's less distortions.
This reinforces in my mind that the interference is being generated by the Javascript being processed in the CPU and the results then processed in the GPU-related subsystem since lower resolution means fewer pixels are being flipped per interval which means lower bitrate which means lower frequency.
Quote:...
Is there more load on the RaspberryPi when:
Do you see more things changing on the screen in one view? That implies more processing (in Javascript).
Quote:
- running a miniDSP 2x4 HD instead of a Dragonfly Red DAC?
See above discussion.
Quote:
- the resolution of the screen is higher?
Yup. See above. More bits implies more processing
Quote:Is the RasPi 3+ inside the USBridge Sig underpowered for the task? I contacted Allo some days ago, still no reaction. I'm trying to get my hands on a regular Raspberry 4 to test this hypothesis.
I can't wait to hear if the miniDSP is susceptible to this noise when coupled to a stock RPi.
Regards,
Kent
[1] Ca 1972 I was using the Maniac III computer at the University of Chicago to cross-compile programs for the PDP-11 I used to control experiments and collect data in my lab.We wizards who stayed up late would put a transistor radio (remember those?) next to the console and try to compose Maniac programs which would cause recognizable if noisy tunes to play on the radio when the programs ran. The chain printer could be used to add a raspy counterpoint.
