This is a small part of The Glossary I Wish I Had™ when I first started exploring sound and music. It’s also a way for me to collect my thoughts and have fun making a little noise.

Sound and Hearing

If a tree falls in the forest, but nobody was around, did it make a sound? This riddle relies on the colloquial ambiguity of the word "sound". Making a distinction between sound and hearing solves the riddle: when a tree falls in the forest, a person standing nearby experiences the objective, measurable sound made by falling lumber as the subjective phenomenon of hearing. It also offers an insight: one way to understand what was heard is to know what sound was made.

🔈 What is sound?

Sound is when vibrations propagate through a medium. These vibrations occur when objects bump or rub each other. The fundamental unit of sound is frequency. Any sample of sound can be represented as a sum of different frequencies.

👂 What is hearing?

Hearing is the phenomenon of consciousness that occurs when sound vibrations that propagate through your body get converted into signal in your brain. When we talk about what we hear, we usually use subjective descriptions - in this case, it’s a recording of someone saying “hello”

〰️ Fundamental Frequency

The fundamental unit of sound is frequency. Every sound is characterized by the frequencies it is composed of, and the phases of those frequencies. Something with a frequency occurs at regular time intervals. Hertz, or vibrations per second, is the common measure of frequency.

Frequency determines pitch.

🎵 Pure Tones

Most sounds that occur in life are composed of many overlapping frequencies. But in some cases, such as a tuning fork, or a synthetic signal, a sound consisting of a single sinusoid can be produced.

👯 Timbre (not to be confused with timber)

If we express the same pitch expressed as a pure tone, or on the piano, or sung out loud, what makes them sound different?

⬆️ Overtones

Timbre is sometimes also used to refer to overtones. Overtones are the higher frequencies that tend to co-occur with a fundamental frequency.

🧮 Harmonics

Harmonics are a special case of overtones where frequencies are a multiple of each other. Musically, these are known as octaves.

🔪 Perspective: hearing is a tiny slice of sound

If a tree falls in the forest and somebody is around to hear it, whatever they hear is merely 1 perspective observing the sound the tree makes; a tiny sample of the sound passing through 1 point in space. Nor can ears capture all frequencies: Humans range from roughly 20 to 20,000Hz with an uneven sensitivity across this spectrum

👽 Phenomena of Hearing

Visualizing Sound

With our biological mechanisms, we often describe sounds with natural language in very abstract ways. But there seems to be much more subtlety that can be teased apart: what kind of tools can help us learn more about the sounds we hear? This was my motivation for Simple Spectrogram App. I knew that a spectrogram could tell me about the sounds happening around me, but it didn’t feel easy to actually make one.

Encoding Information In Sound