What a Sine Wave Sounds Like (And Why It's Unpleasant Alone)

You have heard one

The beep in a hearing test. The tone before an emergency broadcast. A tuning fork, nearly. These are used as references because they are so plain. There is one pitch and you can measure against it.

That plainness is the problem if you want to enjoy the sound. A cello, a voice or rain on a window is never one pitch. Each is a main note with a stack of quieter, higher ones on top, and that stack is what lets you tell a flute from a guitar playing the same note. Musicians call the stack overtones and the result timbre. A sine wave has no stack.

How I learned this the hard way

An early version of my Space world was made of bare sine waves, held for a long time, fairly high up. I thought pure tones would sound clean and airy. They sounded like a whistle that wouldn't stop. I couldn't say why until I understood that there was nothing in them except the pitch.

What gives a sound a body

You add to it. These are the things I ended up adding, and none of them is audible as a separate sound:

• A quiet copy an octave below. It gives weight. More in The Sub-Octave: Where "Deep" Comes From.
• A faint higher tone on top. A little air.
• A second note very slightly out of tune with the first. The two drift against each other slowly, like two singers who are almost together.
• A soft start. No click, no hard edge. More in Attack Time.

Together they read as one sound that has some life in it.

The surprising part

Every pitched sound in my project is still made of sine waves. I use none of the other wave shapes. The difference between the whistle and what is there now is only how many sines there are and how they are layered. Building a sound that way has a name, and I wrote about it in Additive Synthesis: Building a Bell Out of Plain Tones.

A sine wave is fine as an ingredient. It just can't be the whole sound.