I've found that some devices like Kaoss pads can be noisy. (in some of their effects) And here i'm no expert, obviously keep cables away from power cables, even if battery powered. Also some cables (cheap) appear to be noisy in themselves. I think also some pedal effects may be noisy, as I have two multieffects (mooer & korg pandora) which both have noise reduction sections, which if last in the chain will remove noise - hum. However for recording i've found that goldwave will get rid of all noise leaving the sound unchanged. (I sometimes push the recorded signal extremely high in volume which will make any inaudible noise audible)
You sample a chunk of just the noise (a hum) without any other sound and use it in the filter / noise reduction effect. Highlight just a section of just the hum, and copy to the clipboard, now select the whole recording, then go to effects, filter, noise, use clipboard.
I do this before re sampling at a very high volume. It works very well.
Audacity has similar, but haven't used this.
I've also noticed on ebay some very cheap noise reduction devices for car stereos but haven't tried these. I guess there is inherent noise in systems which when amplified become noticeable.
https://www.ebay.co.uk/itm/Car-and-Home-Stereo-Audio-Noise-Filter-Suppressor/274466630643?hash=item3fe77c6bf3:g:40EAAOSwwFZfP9B3 Passive in-line device.
Eliminate ground loop humming and buzzing noise between an audio source and an amplifier.
When used with car audio, this isolation circuit goes between the head unit and the amp or EQ.
£6.41
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