Resonant pole > 20Khz in digitised audio - is my interface broken?

[abbey road d enfer]

no clue ! I cannot hear or even monitor it with my spectrum analyzers... but the sidechain clearly reacts to it.
Yes, I should try fine tuning the cutting point...

You could insert a sharp LPF in the side-chain without altering the main path. That would not be terribly difficult to implement.
If you want to experiment with my 5-stage filter, you're welcome. PM me if you're interested.

 

[abbey road d enfer]

which still strange as a deesser probably have a band pass in the sidechain ?!?

There are two rms detectors in the 902, one is after the High Pass filter, the other receives the buffered input. So both have to deal with HF crap.

 

[JohnRoberts]

which still strange as a deesser probably have a band pass in the sidechain ?!?

de-esser has at least a HPF in the side chain... I wouldn't automatically ASSume a bandpass.

JR

 

[rivermAn]

Hey mate. That's down in the noise, and it's not unusual to see harmonics at those levels high up in the spectrum that are due to interference from power supplies, internally or externally, for a connected device, nearby lighting, a connected device, even if that device isn't connected.

I used Lynx Auroras in a great commercial studio for years where I was also the tech, and they were great. I would often use analysers there and I never noticed any issue like that, that I can remember.

You probably don't have the tools you need to properly test and isolate this, but one thing you can do is get an analyser plugin that will show you more noise so you can see what's really down there. Pro Q isn't really the tool for the job. Voxengo Span is free and usable in this scenario. Get a good look at the whole noise floor, run the unit at 96kHz. Test it with nothing connected to the interface like the other dude said, and if you're using a laptop, try running off battery while you do it. With modern systems, you can get interference like that creeping in from so many different sources. Turn off or unplug as many nearby devices as you can do without, including lights. See if you can make that harmonic vanish.

BTW that's not a pole. A pole is a mathematical concept in filter design. What you have there is a harmonic. It may or may not be due to a resonance in some part of the system, but that kind of peak in the spectrum, with input that has no energy up there, it's not a resonance, unless it's an electrical one that is causing an oscillation, which it won't be.

thanks a lot for this, super helpful

 

[rivermAn]

Update - the aurora is fine. After suggestion from Lynx support I looped the mogami so there was an isolated loop between aurora in/out. In this config, noise spectrum is very small <-120db for all frequencies, and no more harmonics. those weird harmonics must be coming from somewhere else. v glad interface isn't broken.