Question: I've got an input (or recorded track) that is "noisy". How can I eliminate that "noise"?
(N.b.: I'm being a bit loose with terms here. "Noise" here means any unwanted portion of a signal -- whether it's hum, buzz, or just the background "noise" recorded from a live drumkit.)
There are two basic tools in your kit for getting rid of noise.
- Gate
- Expander
Expanders are generally much more natural noise removers. They don't have the same effect on "air" that gates do. If you're not looking for a "natural" sound, this is not a problem -- in fact, lots of people deliberately use gates to give drums more "punch" in a mix. But for certain applications -- especially cymbals and anything that rings out (guitars, pianos, etc) -- an expander is sometimes preferable, so that the sound doesn't suddenly disappear on you.
An expander (basically the opposite of a compressor) "stretches out" the signal beneath a certain threshold, at a ratio you specify. Loud signals are output at the same level, but soft signals are output even softer.
If you were to use a gate set to threshold of, say, -30 dB, then you would "hear" absolute silence between drum beats or notes.
If you use an expander set with a threshold of -30 dB and a ratio of, say, 2 x, then you won't completely eliminate noise. But you won't completely eliminate the "air" either, or the weaker parts of the sample's output.
If a signal comes in at -31 dB, then the expander sends it out at -32 dB. -32 dB -> -34 dB, -33 -> -36, and so on. When you get to about -45 dB inputs you won't really hear anything at all (-60 dB output). But meanwhile the dropoff from the sample input to the dead air is more gradual, more natural sounding.
Incidentally a gate is essentially just an expander with the ratio set to infinity.
Depending on the feel you want to achieve, a drum mix might use the following to eliminate "noise":
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kick -> gate
snare -> gate
tom -> gate
hi hat 'tick' -> gate
hi hat 'ring' -> expander
cymbal -> expander
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mix bus -> expander
For close-mic'ed acoustic drums, I only ever use a gate on the kick drum -- not the snare or toms. My setup for mixing acoustic drums is usually something like:
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kick -> gate at about -15dB
snare -> expander 1:2 at about -40dB
toms -> expanders 1:2 at about -20dB
(sometimes ratio up to 1:4)
hi hat -> expander 1:2 at about -30dB
cymbals -> nothing
- Kick: all that comes out is a big loud "woomf"! No other drums can be heard, except for an occasional hard snare hit.
- Snare: because the snare is such a loud drum (and also when I'm recording it I have 2 mics, one for top and one for the chain), I never raise the snare level very high -- so noise never gets raised high either. I also like to let it ring out as much as possible. So minimizing the amount of expansion really leaves you with a lot of "pyang!", but not much cymbal or toms or kick get into the mix.
- Toms: I hate these drums. I have never figured out a good way of eliminating unwanted signal in the toms -- particularly from neighbouring toms and from the snare. I don't like "boomy" or "ringy" toms so I hit the signal with expansion pretty quick (~ -20 dB) and everything fades quickly. Still not happy with this setup though.
- Hi hat: another loud signal source. Hitting it at -30dB gets rid of light snare hits as well as other cymbals.
- Cymbals: I hate putting even expanders on these unless I have to. The "ring" of a cymbal makes a mix sound very full. So I really don't like eliminating even the weaker parts of the ring. I do, however, put a ton of EQ on cymbals to cut out drum frequencies (especially kick and toms).
Astroman also pointed out Celmo's DeNoiser, which raises another approach to noise reduction. EQ is a very handy tool in getting rid of specific frequency ranges. A notch filter at the right frequency, with the output fed to a gate or an expander, can do wonders for getting rid of hum and buzz.
Hope this is useful. Cheers,
Johann
Will have to try this out in the next few days.
If you put some device *between* the compressor and the expander, that's probably where you'll see some neat-o effects.