Electronics > Beginners

Unwanted digital noise (Not the standard noise floor) from studio monitors

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rsjsouza:
I used to have this issue as well, but it was with the built-in soundcard. Once I got one of those cheapie USB pendrive soundcards (Syba is the one I have) I could record dynamic microphones without problems.

The USB isolator will help with conducted noise but it will be less effective for RFI. If you have a metallic box, you can try to shield your soundcard. Also, check what are the effects of touching a metallic part of your system. Sometimes you get different behaviours by touching different components.

magic:
I won't say it sounds exactly like my PC's ground bounce but it sounds similar. Anyone (who owns a desktop PC, heh) can produce such noise by connecting headphones between the motherboard ground and chassis. Or insert a jack cable into the audio input, press the tip at the other end against the chassis and record.

You have 50Hz mains in Norway, right? So that 120Hz thing isn't from mains but some 7200RPM disk or whatever. Dunno, given that everything else is 900Hz and its harmonics I suspect it's ground bounce rather than RFI from the PSU. But ground noise really should be eliminated by balanced signaling :-//

Failure of safety ground is a rare occurrence, it has never happened to me yet. And if your mains wiring were faulty, there would be no ground loop ;) So it should be safe to try the ground lift at least temporarily to see if it makes a difference, even if I personally wouldn't make such installation permanent without adding some additional protection. You don't need to modify any equipment, only the cable. Use the lousiest and cheapest one you have ;)

Do you have a DMM?

Vildhjarta:

--- Quote from: magic on November 26, 2019, 06:15:24 pm ---You have 50Hz mains in Norway, right? So that 120Hz thing isn't from mains but some 7200RPM disk or whatever. Dunno, given that everything else is 900Hz and its harmonics I suspect it's ground bounce rather than RFI from the PSU. But ground noise really should be eliminated by balanced signaling :-//

--- End quote ---
I tried once more to disconnect my SHDD which is running at 7200rpm, but still the same. :/

--- Quote from: magic on November 26, 2019, 06:15:24 pm ---Failure of safety ground is a rare occurrence, it has never happened to me yet. And if your mains wiring were faulty, there would be no ground loop ;) So it should be safe to try the ground lift at least temporarily to see if it makes a difference, even if I personally wouldn't make such installation permanent without adding some additional protection. You don't need to modify any equipment, only the cable. Use the lousiest and cheapest one you have ;)

--- End quote ---
I'll buy an extra cable set that i can experiment with.

--- Quote from: magic on November 26, 2019, 06:15:24 pm ---Do you have a DMM?

--- End quote ---
No, definitely would come in handy now!

madires:
Another possible source of the buzzing is a SMPSU powering audio stuff. In that case proper filtering of the audio gear's DC power input helps (common and differential mode noise).

Bud:
USB power bus is full if crap. Connect an oscilloscope and see it for yourself. If you power your audio from USB you should change to a standalone power supply as the first step. Eliminate that noise source before doing anything else.

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