Octave + fifth
Early partials overlap often. The ear readily groups them around a common fundamental.
Harmony · Exhibit
Hear a chord
as one note.
Stack two thirds and the ear hears one object with a mood. Build the chord, then retune until the mood shifts.
Build the chord
Major
Partials 4, 5 and 6 already sit inside one octave, and together they make the first major triad the series offers.Partials 4, 5 and 6 already sit inside one octave as the first major triad.
Choose a structure and tap its numbered voices before pressing Play chord to hear them together. Listen for a single chord to emerge from the pitches. Each voice is a ratio above the same root.Choose a structure and try its numbered voices before pressing Play chord, which combines them into one sound.
Why chords fuse
Consonance
comes by degree.
In voices rich in overtones, chords whose tones share many partials fold into one sound.
Two partials close together make the loudness fluctuate. Below about 20 fluctuations a second you hear beating, and above that the sound turns rough.
In the bass the rough zone runs about three semitones, a span musicians call a minor third. Up high it narrows to one, a minor second. Timbre and long listening habits move those limits too.
The voicings on this page use pure ratios, one historically important model. Equal steps and other systems are cultural choices about how to divide the octave.
Add a third
The fifth sets the frame. Lower the middle voice from 5:4 to 6:5 and the chord turns. Acoustics does not settle what that turn means. Both thirds count as consonances, and listeners in this tradition learned to hear the lower one as the darker.
Add dissonance
One tone rubs its neighbour and wants to step down. Let it, and the chord has changed under you. Musicians call that lean a suspension.
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