Octaves & Pitch
An octave is the distance of 12 semitones — the point where a note repeats at a higher or lower pitch. The note C in any octave shares the same musical identity as C in every other octave, just higher or lower.
Pitch Class vs. Octave
Pitch class tells you which of the 12 notes something is (C, D, E, etc.). Octave tells you how high or low that note sounds. A note's full identity requires both: "C4" means the note C in the 4th octave (middle C on a piano). "C2" is the same note two octaves lower — deeper sounding, but still recognizably "C."
MIDI Note Numbers
The music technology world uses MIDI note numbers (integers from 0 to 127) to identify every playable pitch. MIDI 60 is middle C (C4). Each semitone adds 1, so C#4 is 61, D4 is 62, and so on. An octave is always 12 MIDI numbers apart: C3 is 48, C4 is 60, C5 is 72.
To extract the pitch class: pitchClass = midiNote % 12. This strips away the octave and gives you a number 0-11. To get the octave: octave = Math.floor(midiNote / 12) - 1. These operations bridge the gap between "which note" (used for colors and intervals) and "how high" (used for playback and instrument layouts).
A440 — Concert Pitch
The entire tuning system is anchored to one reference frequency: A4 = 440 Hz. Moving up one octave exactly doubles the frequency (A4 = 440 Hz, A5 = 880 Hz, A3 = 220 Hz). This 2:1 ratio is what makes octaves sound like "the same note, higher."
In ChordColor
For chord and interval visualization, ChordColor works with pitch classes (0-11) — whether you play a C3 or a C6, it is still the root and displays the same red color. MIDI numbers become important when the app produces sound, determines instrument range, or places notes on the Studio piano roll.