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How Do Synthesizers Work?

A synthesizer is a machine -- frequently but not always paired with a keyboard -- that can change sounds to mimic different musical instruments. It can also change sounds so that they̵7;re different from any known noise. ̶0;Synthesize̶1; refers to creating something new, frequently out of old parts. A synthesizer creates new sounds and music from old, both by mixing sounds together and by manipulating the sound waves themselves.

The Frequency of Sound Waves
- Three basic characteristics affect the quality and type of a sound: its frequency, shape and ADSR envelop. How high or low a sound is, or its pitch or tone, is determined mostly by how quickly the sound wave vibrates. This is referred to as its frequency. The faster the vibrations, the higher the frequency and the pitch. The energy in those waves is referred to as the amplitude, and produces louder or quieter sounds.
The Shapes of Sound Waves
- The second characteristic that determines sound is the shape of the sound wave. Different instruments generate different shaped waves -- for instance, a trombone makes a zig-zag-shaped sound wave, while an organ makes a box-shaped wave. A pure note, such as would be generated by a tuning fork, has a smooth, undulating profile and is called a sine wave. Musical instruments don̵7;t just produce one primary wave; they also produce other small ones at higher pitches that combine together for a rich, complex sound.
The Profile of Sound Waves
- Each sound has what̵7;s called an ADSR envelop, which refers to variations in amplitude. The four parts are "attack," which is how quickly the sound builds to its maximum volume; "decay," which is when the volume falls slightly; "sustain," the volume it holds at; and "release," how long it hangs in the air once it̵7;s no longer being generated. Different sounds carry different ADSR envelope shapes, and that affects how they sound to our ears -- whether sharp or gentle, grating or mellow.
Mixing it Up
- Synthesizers have the ability to manipulate these three basic characteristics of sound -- frequency, shape and profile. In this way they can change notes from sounding like a flute to sounding like a violin, to a combination of both. Non-musical sounds like car horns or footsteps can be generated as well. The first synthesizers were analog and worked with the actual sound waves themselves with sound-creating modules that could be connected in various ways. Now synthesizers are digital, which means it̵7;s all done via computer chips, frequently on a computer.

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