Audio Frequency to Note Converter

Understanding Frequency & Musical Notes

Every musical note corresponds to a specific frequency -- the number of times a sound wave vibrates per second, measured in Hertz (Hz). Understanding this relationship is essential for tuning, sound design, and mixing.

Equal Temperament

Modern Western music uses 12-tone equal temperament (12-TET), which divides an octave into 12 equal semitones. Each semitone is separated by a frequency ratio of the 12th root of 2 (approximately 1.05946). This means each note's frequency is exactly 2^1/12 times the note below it.

The formula to find any note's frequency is: f = A4 × 2^((n - 69) / 12) where n is the MIDI note number and A4 is the concert pitch reference.

Concert Pitch (A440)

The international standard for concert pitch sets A4 (the A above middle C) to 440 Hz. This standard was adopted by the ISO in 1955. However, some orchestras and tuning systems use alternative references:

• A4 = 432 Hz -- sometimes called "Verdi's A," favored by some for its warmer quality
• A4 = 442 Hz -- commonly used by European orchestras
• A4 = 443 Hz -- used by some Berlin and Vienna orchestras
• A4 = 415 Hz -- Baroque pitch, roughly a semitone lower than modern pitch

Cents

A cent is a logarithmic unit of pitch interval. There are 100 cents per semitone and 1200 cents per octave. Cents are used to measure how far a frequency deviates from perfect tuning. A deviation of +50 cents means the note is halfway to the next semitone (sharp), while -50 cents means it's halfway to the previous semitone (flat).

The formula: cents = 1200 × log2(f / f_exact)

MIDI Note Numbers

The MIDI standard assigns a number from 0 to 127 to each note. Middle C (C4) is MIDI note 60, and A4 is MIDI note 69. Each semitone increments the MIDI number by 1.

Wavelength

Sound travels through air at approximately 343 m/s (at 20 degrees C). The wavelength of a note is: λ = 343 / f. Knowing wavelength helps with room acoustics, speaker placement, and understanding resonance.