How do you remove amp hum from recording

Discussion in 'Recording/Live Sound' started by slackandsteel, Jan 3, 2006.


  1. slackandsteel

    slackandsteel Member

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    I've used a POD to record to in the past but recently have been experimenting with an SM57 close mic'd to my Deluxe Reverb amp. The amp isn't particularly noisy, but like most amps, there is an inherent hum that is always present. I'm recording at low volumes with a clean tone, and that hum is being recorded along with my guitar signal.

    Any advice for getting rid of the hum?

    Thanks in advance,
    Bill
     
  2. MichaelK

    MichaelK Member

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    I use the shortest cords I can (which is tough, since the amp is in a bathroom) and shift my position around till I'm facing a direction that minimizes the hum. If the amp is loud enough and miked well, the hum shouldn't be too intrusive in the mix while you're playing. Some of your favorite records have hum throughout, it's just covered by playing. If there's a quiet section, fade it out at that point or use a noise gate.

    There are plug-ins that can "hear" noise and filter it out, but usually at the expense of the sound. You sometimes get wierd comb filtering and phasey things. I sometimes use Digi's BNR plug if there's a section where hum is too audible, but I don't like to use it too often for the above reasons. You can try something like SoundSoap or Waves X-noise, but that's an expensive solution to a problem that IMO rarely needs fixing.
     
  3. Chiba

    Chiba Gold Supporting Member

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    In my experience, you have to remove the hum before you record, like MK suggests. Removing it after you've recorded is a pain.

    For me, I use more volume from the amp, which creates a higher signal to noise ratio in the recording, and in addition to what MK suggests, allows me to more easily edit the beginnings & endings of my tracks to eliminate the noise. My guitars are also shielded within an inch of their lives.

    --chiba
     
  4. MichaelK

    MichaelK Member

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    >> My guitars are also shielded within an inch of their lives.

    Definitely a big help. I have a LP with P90s that was impossible till I shielded the control cavity.
     
  5. Greggy

    Greggy Member

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    Experiment with the tubes, some are quieter than others. Also, I concur that recording at higher amp volumes increases the signal to noise ratio, which should help. Finally, often hum hurts my recordings when the guitar is fading out at the end of a piece (signal to noise ratio is decreasing). In that situation, just carefully trim your tracks in your track editor. Like you, I am currently recording clean guitar tracks for a song. I had a similar hum problem last night, and after confirming there were no ground loops in the chain I simply raised the master volumes and lowered the gains on the amps (recording a stereo amp rig with a stereo chorus out front). The increased signal to noise ratio and careful track trimming eliminated the problem.
     
  6. LHanson

    LHanson Member

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    How old is the DR? Vintage ones need to be recapped, if it hasn't been done already. I guess the reissues are getting old enough to need power supply caps as well?

    Does it hum with nothing plugged into the input?
     
  7. wooldl

    wooldl Member

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    I agree with MichaelK - The hum shouldn't be audible while you are playing and once added to a mix. You can also zero out the track in the 'no play' sections.
     
  8. andyc

    andyc Member

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    I'm probably not really adding anything to the other fine responses here, but my input would certainly be to locate the source of the hum. You have responses that talk about power supply hum inside the amp, and replacing the large electrolytic caps in the power supply is certainly the correct fix there in most cases. Also, improving the shielding on the guitar will reduce the noise picked up through the guitar itself.

    As one writer suggests - unplug the guitar and cable from the amp and see if the amp still produces the hum you are describing. If it does, the hum is likely from the amp power supply, and likely can be reduced by a qualified tech either replacing the caps or increasing the power supply filtering.

    If the hum goes away with the guitar cable unplugged - the problem is with the cabling, connectors or shielding and can be addressed differently.

    The hum is at 60 Hz (and multiples of 60 Hz), so is within the sonic range of the guitar and amp. There is no really great way to eliminate the 60 Hz hum in the recordings without eliminating the other desired audio at 60 Hz in the music.

    Too many words to say what the others have sad - solve the problem before recording.
     
  9. joseph

    joseph Member

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    You probably already know this, you'll get more hum if you're sitting with your guitar (or a cell phone) close to the screen monitor.
     
  10. slhguitar

    slhguitar Member

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    Another way to eliminate it (other than raising the signal-to-noise ratio) would be to take a parametric EQ, and notch out only the 60 HZ mark.....If it is the hum that is inherent to all electrical devices, it will be coming mainly from the fact that north american power is 117 V AC at 60 HZ. This should get rid of it right away, without actually affecting your tone.
     
  11. MichaelK

    MichaelK Member

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    Nice thought, but it doesn't work that way. "60 cycle hum" is not a neat 60 Hz. wave that you can just dial down. It's mainly that plus the 2nd and 3rd harmonics at 120 and 180 Hz., respectively. Try dialing down all three and see if that doesn't affect your tone.
     
  12. enharmonic

    enharmonic Old Growth Gold Supporting Member

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    Use a gate. If it's real bad, take a look at the lighting in your recording environment. Flourescent lights are evil. Lights on dimmers are evil. Neon lighting is evil. Power strips can be evil.
     
  13. mccreadyisgod

    mccreadyisgod Member

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    Another reply in the stupid-but-worth-mentioning vein: Play with the amp's Ground switch and see if that affects the hum level. Avoid playing with flourescent lighting or computer monitors around. Try a power conditioner for the amp (and if possible, any pedals; I use a Voodoo Labs Pedal Power II which killed an enormous amount of hum).
     

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