jack hiss at 1000 Hz

[gauthier]

I can hear a hiss in the applications using jackd: Jamulus, Audacity, Ardour. It's hearable but ok with a clean signal, but gets annoying when I e.g. add compression with jack-rack.

Audacity's frequency analysis tells me it's around 1000 Hz.
Where I was expecting white noise, this is what I got:

Screenshot from 2020-07-19 01-20-50.png (228.03 KiB) Viewed 678 times

Screenshot from 2020-07-19 01-22-45.png (37.6 KiB) Viewed 678 times

Less visible but still there without jack-rack:

Screenshot from 2020-07-19 01-25-19.png (22.41 KiB) Viewed 677 times

Jack settings:
Sample Rate 48000
Frames/Period 64
Periods/Buffer 4

Changing Audacity's Project rate from 44100 to 48000 Hz affects the frequency of the noise, but it's still there. Same for changing Frames/Period to 128.

Is this known behavior? Something I could do about it?

[bluebell]

I have that hissing on the output of my headphone amp. On my system it's due to a ground loop that happens when there are at least 2 devices grounded (power cable with earth connection) AND connected with non-symmetric cables (mono jack, cinch).

Sometimes it can be (partitially) cured with a 1:1 transformer, like https://www.amazon.de/gp/product/B017HBBOP4/

But the real thing is symmetric/balanced cableing.

[gauthier]

I didn't want to believe this. How arrogant of me. I've recorded a little with PulseAudio on that setup, and never noticed the 1 kHz. Now that I'm looking for it, I see it's there with PulseAudio too, although much quieter (I have a hard time hearing it in silence).

So then I looked at my mixer again, and yes, its output goes to my amplifier, with a stereo RCA cable pair.

Computer/soundcard ground, amplifier ground, both go to my mixer.

I disconnected the amplifier (I'm using headphones directly from the mixer) and the noise is gone. Thank you so much!

That might be a problem since I still want to connect my computer output to the amplifier most of the time, but not having to rewire for music work would be a luxury.