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No. 2588:
Synthetic Sound Waves

by Andrew Boyd

Today, the sound of music. The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.

When someone speaks their vocal chords vibrate. That sends sound waves through the air. It's just like dropping a rock in the water and watching the waves move out in a circle.

For every different sound, there's a different wave. A microphone is really just a sound wave recording device. When I record an episode of the Engines of Our Ingenuity, I get to watch the wave drawn in real time on a computer screen. There it is — my voice, captured as a picture of a wave. With a little practice, you can pick out words just by looking at the wave on the screen.

sound waves
"The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them," as spoken by the author.

sound waves
A close up of the word "Houston's."

sound waves
A close up of the letter "O" in "HoustOn's." Notice the regular, complex wave pattern

Just as microphones are recording devices, speakers are playback devices. Send a wave to a speaker, and it will vibrate according to the shape of the wave. It's actually remarkable that this record/playback system works so well. With just a twenty dollar microphone and a similarly inexpensive clock radio, we recognize music, words, inflections. And at the center of it all is a sound wave stored in a computer.

Which leads us to ask: rather than record a sound wave and play it back, can't we just create one on the computer and skip the recording? In fact, we can. We call this process sound synthesisSynthesizers are machines or computer programs that create sound waves from scratch, so to speak. They have a multitude of knobs for shaping sound waves — for taking one wave and twisting it into another. Music synthesis can produce almost limitless sounds, including many that we can't find in nature. 

Music synthesis and synthesizers are often associated with strange sounds.

(Audio of strange sounds)

Musicians that work with synthesizers often choose unfamiliar sounds for just that reason: they're unfamiliar. Why try to imitate what's already been done? But synthesizers don't have to make strange sounds. 

(Audio of not-strange sounds)

In theory, synthesizers can replicate the sound of traditional instruments — for example, a violin. But the timbre of a violin and the nuance of the musician yield an incredibly complex sound wave — a wave so complicated it's far easier to record a violinist than attempt to synthesize the sound of a violin.

With the palate of sounds that can be produced, synthesis is a catalyst for musical creativity. Where will it lead? We'll have to wait and see. But the technology for making and shaping sounds marches steadily forward.

I'm Andy Boyd at the University of Houston, where we're interested in the way inventive minds work.

(Theme music)

Notes and references:

For related episodes, see 557, MUSIC: REAL OR FAKE?; 1929, SWITCHED ON BACH; and 2296, ROBERT MOOG.

Digital audio, which is now the dominant way in which music is recorded and transferred, stores sound waves as binary files on a computer. This is not true of analog audio, where sound waves are stored on a medium such as magnetic tape without conversion to digital form. Technically, sound synthesis doesn't rely on a "sound wave stored in a computer." It simply consists of a "sound wave on a storage device" that is manipulated and/or generated through mechanical means, not by recording. In the interest of simplicity, I have loosely used "computer" instead of "sound wave storage device."