How sound works

Everything in this course comes down to air moving back and forth. A speaker cone pushes and pulls the air, and your eardrum follows. Three properties describe what you hear.

Frequency is pitch

Frequency is how many times per second the air vibrates, measured in hertz (Hz). The A above middle C vibrates 440 times a second. Double the frequency and you get the same note an octave higher (880 Hz); halve it and you drop an octave (220 Hz). People hear from roughly 20 Hz to 20,000 Hz. The bottom of that range matters more than anything for this course: a dub sound system is built to move air at 40 Hz, and a techno kick does most of its work between 45 and 100 Hz.

Amplitude is loudness

Amplitude is how far the air moves. We measure it in decibels (dB), which is a logarithmic scale: +6 dB is double the signal level, and about +10 dB sounds twice as loud. In your software, 0 dB is the ceiling. Push past it and the signal clips, which sounds harsh and broken.

Timbre is the harmonics

A piano and a synth playing the same A sound different because of what rides on top of the main pitch. Almost every musical sound contains a fundamental (the pitch you name) plus harmonics at whole-number multiples of it: for A at 110 Hz, harmonics sit at 220, 330, 440, 550 Hz and up. Which harmonics are present, and how loud they are, is the timbre, the color of the sound. Synthesis is mostly the craft of adding and removing harmonics.

The four basic waveforms

Synths start from simple repeating shapes. Each shape has a fixed recipe of harmonics:

• Sine: only the fundamental. Pure and round. This is the sub bass in dub and the body of an 808 kick.
• Triangle: odd-numbered harmonics (3rd, 5th, 7th) that fade quickly. Soft and flute-like.
• Square: odd harmonics, much stronger. Hollow, woody, reedy: organs, clarinets, the reed buzz of an accordion.
• Sawtooth: every harmonic. Bright and buzzy. The raw material for chords, strings, brass and acid lines.

Where things live in the spectrum

Mixing is mostly about giving each sound its own frequency range. Learn this map; you will use it every day.