Can Filtered Noise Have a Pitch? What Happened When I Tried

Why I wanted it

The Space world gave me trouble for a long time. Whenever I built its notes from plain tones, it came out sounding like Forest: bells and bowls again.

I wanted something that could not sound like a bell. Noise can't, because it has no pitch. So I had an idea. What if the notes were made of noise, squeezed until they almost had a pitch?

How noise gets a pitch

A band-pass filter keeps one slice of a sound and removes what's above and below it. I went through the basics in carving sound out of noise.

A wide slice of noise sounds like air. Make the slice narrower and it begins to whistle, with a pitch you could hum along to. MDN describes the setting that does it: it "controls the width of the frequency band. The greater the Q value, the smaller the frequency band."

On paper I had my new instrument. Tune the slice to each note of the scale and play them together.

What went wrong

It was faint. Noise spreads its loudness over every pitch at once. A narrow slice keeps a sliver of that and throws the rest away. The more pitched I made it, the quieter it got. Turning it up mostly turned up the hiss around the note.

It was blurred. Even a narrow slice is a small crowd of neighbouring pitches jostling each other, so the note flutters and never settles. One on its own was pretty, in a ghostly way. Three together, meant as a chord, smeared into a hiss with a vague colour.

It had no depth. A slice only contains what's inside the slice. In Ocean the feeling of depth comes from a lower tone sitting under each note, which I wrote about in where "deep" comes from. I couldn't filter that weight in afterwards. The harmony floated, thin, with nothing under it.

The short sounds were the worst. For the brief ones I snapped a burst of noise into a narrow filter and hoped for a small ping. What came out was a sharp click at the front and almost nothing after it. Sharp and nasty were the words I used at the time.

What I did instead

I went back to plain tones and built Space's harmony the way Ocean's is built: a note, a lower tone under it for weight, and a near twin a hair away, so the two slowly pulse against each other.

I expected it to turn into Forest again. It didn't. What makes Forest sound like Forest turned out to live around the notes, not inside them: its scale, its steady pulse, its fifths. Space had a scale with no home note, no pulse, a long echo and no fifths anywhere. With all of that in place, tones built like Ocean's sounded like neither of the other two worlds.

Where pitched noise still earns its place

I didn't throw the idea out. It works when a hint of a note is all I want.

• The static and crackle in Space are noise through a band. They are pitchless on purpose, so they can never clash with the harmony.
• Forest has a hollow, hall-like texture made from noise through a narrower band. It is meant to sound like a big room quietly humming to itself, and a vague pitch suits that.

The rule I took away: filtered noise for a hint of a note, tones for a note.

Sources

• BiquadFilterNode, MDN