From MIDI notes to frequency
MIDI note 69 is A4. Each increase of 12 MIDI notes doubles frequency, and each semitone multiplies it by the twelfth root of two. This describes twelve-tone equal temperament, the default tuning used by most modern MIDI instruments and DAWs.
Changing the tuning reference
A4 = 440 Hz is common but not universal. Some ensembles use a slightly different reference, and historical or stylistic work may use other systems. Adjusting A4 shifts every calculated equal-tempered note together.
Using frequencies in production
The values help set oscillators, filters, test tones, and pitch-aware processing. An acoustic instrument contains harmonics and changes through time, so its identity cannot be reduced to the fundamental frequency alone.
Tuning limitations
Just intonation, meantone, stretched piano tuning, and non-Western tuning systems do not follow this formula exactly. MIDI note numbers can also trigger samples whose recorded pitch or mapping differs from the nominal note.
How the calculation works
Frequency = A4 × 2^((MIDI note − 69)/12) for twelve-tone equal temperament.
