White noise

White noise is every frequency sounding at once, at random, with none louder than the rest. You hear it as a steady hiss, close to a radio tuned between stations. The name borrows from light: white light holds every color, and white noise holds every frequency in equal amounts per hertz. The top octave of hearing, 10 to 20 kHz, is 10,000 Hz wide, while the octave from 100 to 200 Hz is only 100 Hz wide. So the high end carries far more of the energy, and white noise sounds bright and fizzy.

Pink noise evens out that tilt. Its power falls 3 dB per octave, so every octave carries the same energy, and it sounds deeper and softer, closer to steady rain. Brown noise is named after Brownian motion, not the color. It falls 6 dB per octave and sounds like a low rumble.

How synths use noise

On a synth, noise is a sound source beside the oscillators, with its own level. It has no pitch, so a higher key does not make it higher (unless the filter is set to follow the keyboard). The filter and the amp envelope do the shaping:

• Hi-hat: noise through a high-pass filter set around 7 kHz, with an amp decay of 30 to 80 ms for a closed hat and 300 ms or more for an open one.
• Snare: a short burst of noise, about 150 ms, layered over a pitched thump near 200 Hz.
• Wind and surf: noise through a low-pass filter, with a slow LFO sweeping the cutoff up and down.
• Pick and mallet attacks: 5 to 10 ms of noise at the start of a note, mixed low. A little noise held under a flute sound adds breath.

Synth filters explained covers the cutoff and resonance moves behind these, and how to make a pluck synth uses a noise burst for the attack.

In Gelato Synth, the Noise page has three sliders: Level, Tone (dark to bright) and Burst, a short burst of noise for pick and mallet attacks.