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Removing mains hum from guitar samples

Quarkstar
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permalink   Wed, May 15, 2013 @ 11:41 AM
A quick and dirty look at reducing mains hum on samples.

Mains hum is generally caused by poor earthing or electromagnetic pickup. If its poor earthing then try plugging all your effects, computer and amps into one mains extension. The hum can also be caused by an earth loop which is beyond the scope of this.

If it Is pickup, try and keep your signal leads (guitar lead, microphone lead) away from the mains leads. Adding clip-on ferrite cores to the mains lead of the amplifier may help, these are pretty cheap and worth trying.

Assuming the sample contains mains hum, it will be at 50/60Hz (Europe / USA) and at multiples of that (120, 240, etc). For lead guitar simply add a high pass filter at 200/240Hz.

If the guitar is lower pitched then use two notch filters at 50/60Hz or 100/120Hz.

You can’t use notch filters on bass guitars as it will affect the sound of the bass. You may be able to use a Gate.

There will also be a high frequency component to the hum, if the guitar isn’t too high pitched, roll off the high frequencies with a low pass filter with a setting that it doesn’t affect the guitar sound too much.

If the hum falls into the frequencies used by the guitar your can use a Gate in your DAW. Set the gate to cut off the quiet parts of the notes along with the noise.

If you have a sustain effect on your guitar and the noise gets louder as the notes fade, you can’t do much. This type of hum should really be removed at source.

If you can plug your guitar directly into a USB converter there shouldn’t be any hum. Then you can use a Guitar Amp simulator to get the sounds.

(Edited with minor corections as the original was typed at 1am)
annabloom
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permalink   Sat, Nov 2, 2013 @ 7:10 PM
another way -although it requires more trial&error- is to change the phase:
(tested in Reaper)
- load the file into two tracks
- reverse the phase in one of them
- the result should be silence
- now apply an effect such as compressor or reverb to one track
- you now hear the signal generated by the effect
- the trick is to choose an effect that does not affect the hum frequencies
As I said, requires a bit of tinkering but works in principle
stellarartwars
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permalink   Sat, Feb 22, 2014 @ 11:44 AM
On this issue I’m interested in a problem relating to some of my outboard gear. Two rackmounts use US rather than UK power supply, and if I have them and their step-down transformer powered up earth hum becomes very noticeable. Even if I mute them on the desk, without physically disconnecting them, I get the problem.
 
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permalink   Quarkstar Sat, Feb 22, 2014 @ 3:38 PM
Check you have an isolated step down transformer. I think this explains http://sound.westhost.com/a...
 
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permalink   stellarartwars Sun, Feb 23, 2014 @ 10:08 AM
Seems only these are legal in the UK and I got mine from a reputable dealer. What’s interesting (and something I didn’t know) is the AC frequency of mains is 10Hz less in the UK, this may have something, though I will have to check the details, not au fait with transformers. One suggestion in your excellent link is rewiring two pin cables and connectors with three pin earthed ones. I’ve known this to work. Some get rather too casual in music when it comes to proper earthing in an attempt to remove hum, unfortunately a friend of mine was left paralysed through a guitar amp electrocution.
 
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permalink   Quarkstar Sun, Feb 23, 2014 @ 10:16 AM
Hum is an indication that something is wrong and your mention of two pin cables scares me. I would get an electrician in to check it.

At work we had mixtures of 240V ac, 110V ac, 24V dc. We always had qualified electricians set it up.