SC 2014 Semilab: Electricity and Sound

by Alex Treyer

If you ever stood close to a big subwoofer while it was playing a tune, you may have realized that sound is some sort of a mechanical wave that makes the air vibrate as it passes through, and that you feel these vibrations with your ears, or chest, depending on how loud you like your music. In fact, most musical instruments are built in a way that allows them to generate and give off specific vibrations, controlled by a playing musician, to the surrounding air. The qualities of sound waves an instrument can produce are defined by its mechanical components (e.g. the strings, the wood, the brass, the drumheads, the list goes on). At the beginning of the twentieth century, scientists and engineers studying effects of electricity discovered that electric current could be used to control vibrations of certain mechanical components of machines, and that such electro-mechanical machines were capable of producing sound in a way much like a musical instrument, by tuned changes in their electric current. Later, in the 1950s, physicists and musicians together began making, or synthesizing, sound by designing custom waves of current. The key feature of their idea was that a sound wave could be given any shape you wanted it to have, so long as you could first make that shape as an electronic wave signal. To this day, their concept continues to make for a tremendous variety of sounds possible, to the great joy of electronic musicians worldwide. But what do we need to do if we want to shape electric current and transfer it into sound?

Our series of semilabs will focus on understanding and putting together the key components that make up an analog circuit-based sound synthesizer, much like the simplest synths of the 1950s. We will go over wave generation, amplification, and filtering, and will try to visualize various waveforms we can produce. We will look at the qualities that a sound can have to the ear, and how these qualities are carried in the wave shape. We will attempt to wire up some circuits first hand, of course, or use pre-wired examples for the more complicated engineering parts. This lab will will give you a basic appreciation for both the fun and the hard work of designing sound with electric circuits.

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