Noise: Avoid It, Then Reduce It Carefully

Noise reduction is a subtraction. The software guesses which part of the sound is noise and takes it away. When the guess is good and you ask for a modest amount, it works. When you ask for too much, it starts taking bits of the voice along with the noise, and the result sounds worse than the noise did.

So the order is fixed. First avoid noise. Then identify what is left. Then reduce it, gently.

Know what you are hearing

Put on headphones and turn the playback up a bit higher than usual while you listen to a gap between sentences. Most noise you will meet is one of these. The SoundStudio theory page has a table of them at Noise: hiss, hum and rumble.

You can also see noise. In SoundStudio press V to switch the view to Wave + Spectrogram. Time runs left to right, frequency bottom to top. Hum shows as a thin steady horizontal line low down (with fainter copies above it). Hiss is a haze across the top. A click is a thin vertical line through everything. Rumble is a glow along the very bottom edge (the view starts at 50 Hz, so the deepest rumble sits just below it).

Avoid it at the source

Every fix here beats every plugin.

• Hum: move audio cables away from power cords and cross them at right angles if they must meet. Plug the interface and computer into the same outlet strip. Try a laptop on battery: if the hum vanishes, it was the charger.
• Hiss: get the mic closer so you need less gain. Hiss rises with the gain knob. Moving from 12 inches to 4 inches lets you drop the gain by a lot.
• Rumble: use a shock mount or put the mic stand on a folded towel. Don't tap the desk. Record when the trucks aren't running.
• Room tone: turn off the HVAC for the take, close the window, unplug the fridge if it is close (and stick a note on your car keys so you plug it back in).

Then record those 10 to 20 seconds of room tone from lesson 1. You need it for the next step.

Quick fixes for specific noise

The Noise tab in SoundStudio has a Quick Noise Removal group. Each button is a fixed filter, and like everything in SoundStudio it only happens when you click it. Each works on the selection if there is one, otherwise the whole file.

• Remove Hum notches out 50, 60, 100 and 120 Hz.
• Remove Rumble cuts below 80 Hz. Speech has almost nothing down there, so this one is nearly always safe on a voice.
• Remove Wind cuts below 200 Hz. Stronger. It will thin a deep voice, so use it only on outdoor recordings that need it.
• Remove Hiss rolls off above 7 kHz. That also dulls the crisp top of S and T sounds, so listen before and after.

If the hum sits at some other frequency (a buzzy 180 Hz, say), you can find it in the Spectrum tab and cut it with a Notch band in the EQ, which lesson 4 covers.

Spectral Noise Reduction, step by step

For steady broadband noise like hiss, fan noise or general room tone, use Spectral Noise Reduction in the Noise tab. It works from a noise profile: you show it what the noise sounds like alone, and it subtracts that much of each frequency from the whole file.

1. Find a stretch of noise only. Your room tone clip is ideal. Otherwise, a pause between sentences. Half a second or more works best. No breaths, no word endings.
2. Select it and press 1. Capture Noise Profile.
3. Click once on the waveform without dragging to clear the selection (so the next step covers the whole file), or select just the part you want to clean.
4. Set Reduction and Smoothing. Start moderate. The theory page suggests 50 to 70 percent as a starting point.
5. Press 2. Apply Noise Reduction.
6. Listen. Then press Ctrl+Z and Ctrl+Y a few times to flip between before and after on the same sentence.

What over-processing sounds like

Learn these by ear so you hear them before your listeners do.

• Musical noise. Little chirps, twinkles and a watery warble in the gaps and around words. The noise is random, so the subtraction misses in random places and leaves small bits sticking out. The theory page calls it out by name.
• Underwater or phone voice. The voice loses its top and its body, as if it went through a cheap speaker. The reducer is eating frequencies the voice shares with the noise.
• Swallowed endings. Soft consonants at the ends of words (the "s" in "rates," the "t" in "vote") vanish.
• Pumping. The background rises and falls with the voice, louder in gaps, quieter under words.

If you hear any of these, undo and try again with a lower Reduction. Two light passes with a fresh profile can be cleaner than one heavy pass, but the real fix for a very noisy file is a re-record.

Gates are not noise reduction

The Gate in the Dynamics tab turns down anything below a threshold, which hushes noise between phrases. It does nothing to noise under the words, so a gated noisy track can sound worse: hiss, then silence, then hiss again every time someone talks. SoundStudio's help says that when you press Fit to This Audio, the gate is left off if the room noise is within 18 dB of the voice, because it would chop words. If you use a gate on voice, set Range to -10 to -20 dB instead of Mute, so the gaps just get quieter. Clean the noise first; gate second, if at all.