Got a noisy mic or a lot of background noise in your recordings? Never fear! Noise Gate (and his sidekick wonderboy Compressor) are here!
Noise is a hissing or hum in your recordings that can be very distracting or cause serious problems when editing together clips. A noise gate is a device that automatically reduces the volume on a recording when it drops below a certain volume. It’s kind of like if you turn the volume knob on a radio. You turn it up when someone is speaking, and turn it down when it goes to commercial. A compressor is a device that squishes (or compresses) the volume of a recording, making the quiet parts louder and the loud parts quieter. Going back to the volume knob analogy, this is like when the radio gets too loud and you turn it down, or it’s too quiet and you turn it up. Using these two devices (and some EQ), you can make a noisy recording sound much better.
I will be using screenshots from my own audio editor, Apple Logic Express, but the basic ideas and methods are the same in any audio editing software.
First you need to make sure your recording is normalized. This means that the audio is turned up as loud as it can go without clipping. Clipping is when a recording is so loud, that it pops or crackles. If you’ve ever turned up a song way too loud on a stereo, you’ve heard clipping. Audio equipment has a certain limit of how loud something can be. When it can’t play a sound because it’s too loud, it clips it, which causes the pop or crackle.
Some audio editors (like Logic) have a Normalize function which will do this automatically.
If your audio editor doesn’t have this feature, you’ll have to manually set the volume (also sometimes called the gain) of the recording while watching your volume levels meter. Clipping occurs whenever the recording goes above 0.0 dB.
Next we’ll add the noise gate to the recording.
The threshold is how loud the recording must reach to disable the noise gate. Anything below the threshold will be blocked by the noise gate. The reduction is how much the noise gate will decrease the volume. The attack, hold, and release pertain to how the noise gate behaves. Attack is how quickly the noise gate is disabled. A shorter attack means the volume will jump up quicker. Hold is how long the noise gate should stay disabled after the recording drops below the threshold. Release is how long it takes the noise gate to reduce the volume back down to the reduction level. It takes a bit of experimentation, trial and error to find the correct settings. Make sure the noise gate works for the entire recording, or split the recording into several sections with different noise gates.
Now that the noise gate is set, all of the noise in between is gone, but when the volume crosses the threshold, we can still hear the noise.
This is where we need an equalizer (EQ). The equalizer lets us alter the volume level of specific frequencies, which in turn alters the sound of the recording. Again, there’s a lot of experimentation with this. You’ll have to fiddle with the EQ to isolate and reduce the specific frequencies that are causing noise in your recording. Be careful not to do too much EQ. You want to reduce the noise without heavily harming the sound of the recording.
The last step is the compressor.
The compressor will squish the sound of the recording, and with the right tweaking of all three devices (noise, EQ, compressor), the compressor can squish the last bits of noise out of the recording. Similar to the noise gate, the threshold is the volume level the recording must reach to activate the compressor. The attack and release dictate how the compressor will behave. The other important control here is the ratio. The ratio determines how much the sound will be squished. A ratio like the one above (2.2 : 1) means that every 2.2 dB of volume gets compressed to 1 dB. Meaning a recording with a volume of 6.6 dB becomes 3 dB. A high ratio ensures a more constant volume throughout the recording. If the ratio is too high, you’ll hear every little noise that makes it through the noise gate, which sounds unnatural and kind of gross 😛
Like all audio editing, it takes a lot of fiddling around, experimentation, and hard work to get it to sound good. Using these three tools together can clean up a noisy recording pretty well with minimal effort.