How musical instruments work

There are a lot of different musical instruments out there. Just about all of them share four basic components: a harmonic oscillator, a source of noise, a control surface for modulation, and a resonator.

A harmonic oscillator produces sine waves, or their mathematical cousins sawtooth and square waves. For most of technological history, our oscillators were mechanical systems of skins or reeds or metal. For the past hundred-ish years we’ve also been using electronic oscillators connected to speaker cones. Making a steady mechanical oscillator is expensive and challenging. Even making a reliable tuning fork or pendulum takes some crafty engineering. A side benefit of the computer revolution is that we’ve figured out how to mass-produce very cheap electronic oscillators out of quartz crystals and microchips, so now we’re surrounded by them in our cell phones and computers.

Sine wave oscillations are thermodynamically unlikely and hard to produce. Noise is everywhere and easy to produce. In mechanical systems the big challenge is to limit it. In electronic systems, pure sine waves are easy to make and sustain. Now that we’ve had a chance to listen to them, we’ve come to appreciate the musical value of noise better. Pure sine waves sound unearthly and fake. Part of what gives a cello its distinctive tone is the noise of the bow scraping against the strings. Percussion is mostly shaped noise.

Once you have your blend of sine waves and noise, you want to be able to control when they start and stop, how loud they are, and what pitch they’re at. Ideally you also want to be able to shape the overtones to give nuance to your tone. In mechanical instruments the control surface is the whole object. In electronic systems, the control surface and the sound generation system can be totally separate devices. Using computers it’s possible to produce any recorded or synthesized sound at all from a keyboard or even video game controllers and cell phones.

Finally, you probably need to boost your signal to make a loud enough sound that people can hear it. For that, you need a resonator, something that vibrates sympathetically with your signal. For electronic instruments the resonator is an electronic amplifier hooked to speakers, headphones or the business end of a recording device.

Here are some widely-used music tools in terms of the basic four components.

Your voice

• Oscillator: vocal folds
• Noise: plosives and fricatives
• Modulation: shape of mouth, position of tongue, lips and teeth
• Resonator: chest, sinus cavities

Beer bottle

• Oscillator: air at bottle mouth
• Noise: overblowing
• Modulation: blowing angle and intensity, amount of water inside
• Resonator: bottle interior

Clarinet

• Oscillator: reed
• Noise: overblowing
• Modulation: keys, embouchure
• Resonator: body

Piano

• Oscillator: strings
• Noise: none, unless you put ball bearings or something on the strings
• Modulation: timing and intensity of key presses and releases, sustain pedal
• Resonator: body

Acoustic guitar

• Oscillator: strings
• Noise: pick scraping, strings buzzing against fretboard
• Modulation: fingers on fretboard, pick angle and attack
• Resonator: body

Electric guitar

• Oscillator: strings, amp speaker driver
• Noise: pick scraping, string buzzing, amp distortion, electrical interference
• Modulation: fingers on fretboard, pick angle and attack, whammy bar, tone switches and knobs, effects units and expression pedals, amp settings…
• Resonator: amp speaker cone

Snare drum

• Oscillator: drum head
• Noise: snares
• Modulation: angle, location and intensity of whacking, makeup of striking implement (wood or rattan sticks, brushes, mallets, bare hands, etc)
• Resonator: body

Record player

• Oscillator: needle in the groove. The groove is shaped by the electromagnetic oscillations captured on the master tape, which follows the electrical signal from the microphones and mixing console in the original recording, and so on.
• Noise: dust on the needle and in the groove, electrical interference
• Modulation: speed knob, DJ scratching and crossfading
• Resonator: speaker cone

Drum machine

• Oscillator: Electromagnetic oscillators and crystal clocks
• Noise: Electromagnetic noisemakers
• Modulation: Buttons and knobs
• Resonator: speaker cone

Nintendo Entertainment System

• Oscillator: Electromagnetic oscillators and crystal clocks
• Noise: Electromagnetic noisemakers
• Modulation: Software on the game cartridge controlling voltages on the oscillators and noisemakers, as specified by the assembly language translation of Kōji Kondō’s score
• Resonator: TV speaker cones