Hearing Intervals
A proof of concept. Every pitch is synthesised in your browser, so this book ships no audio files at all.
Music theory is usually taught to the eye. You are shown a diagram, told what it is called, and left to imagine what it sounds like. This page does it the other way round: every example here is an instrument, and nothing is explained before you have heard it.
Start by playing
Click any key. The black keys are not centred between the white ones — look closely and you will see the C sharp leaning toward C, the D sharp toward E. That asymmetry is not decoration; it is what lets a hand find its way without looking.
The interval that sounds stable
Two notes played one after another make an interval, and the distance between them is what you hear. Play the pair below. It sounds settled, almost like one sound rather than two — this is a perfect fifth, and it is the interval most human music is built on.
Count the keys between them, black and white together, and you will find seven. That number is the whole definition. Move both notes up by the same seven semitones and the character survives intact, which is why a fifth sounds like a fifth no matter where you begin.
Move one note, change everything
Now take the upper note down by a single semitone. The gap narrows from seven to six. That is one key's difference on the instrument, and the entire character collapses — where the fifth sat still, this refuses to. Medieval theorists called it the devil in music, and it is the sound almost every siren and alarm is built from.
Three notes at once
Stack a third interval on top and the two-note relationship becomes a chord. Played together rather than in sequence, the three pitches fuse into a single colour — the major triad, the most common chord in Western music. You have heard it several thousand times today already.