How note frequency works #
In twelve-tone equal temperament, each semitone changes frequency by a factor of 2^(1 ÷ 12). The calculator treats A4 as MIDI note 69 and uses A4 frequency × 2^((MIDI note − 69) ÷ 12) to convert a note into hertz.
For the reverse calculation, it finds the nearest equal-tempered note and reports how far the entered frequency sits above or below it. The cents deviation is 1,200 × log2(entered frequency ÷ nearest-note frequency). Zero cents is exactly in tune; positive values are sharp and negative values are flat.
MIDI notes and octave names #
The calculator uses scientific pitch notation: middle C is C4 and MIDI note 60, while A4 is MIDI note 69. Each octave adds 12 MIDI notes and doubles the frequency. You can edit either the note name or its MIDI number; the inputs stay synchronized. The selector accepts the standard MIDI range from C-1 (MIDI 0) to G9 (MIDI 127).
Frequencies outside that range can still have a mathematically nearest note name. When that happens, the result identifies the extended note number rather than presenting it as a standard MIDI note.
Using adjustable A4 tuning #
The default reference is A4 = 440 Hz. Changing A4 shifts every calculated pitch by the same ratio, which is useful when matching instruments or recordings tuned to another reference such as 432, 442 or 444 Hz.
The tuning control accepts 400–480 Hz. It changes the reference system; it does not pitch-shift audio or decide whether a recorded note is musically in tune.
Period, octaves and wavelength #
Period is one complete waveform cycle, calculated as 1,000 ÷ frequency milliseconds. It can help relate oscillator pitch to short delay, comb-filter or modulation times, though phase and device behaviour still affect the sound.
The octave references show the same pitch class one octave below and above the result. Their frequencies are half and double the centre frequency.
Wavelength is calculated as 343 ÷ frequency metres, using 343 metres per second as an approximate speed of sound in dry air near 20 °C. Temperature and the transmission medium change the real value.
Sound-design uses and limits #
- Use the note-to-frequency result to set an oscillator, resonant filter or test tone to an equal-tempered pitch.
- Use frequency-to-note and cents deviation to inspect a sustained fundamental, then tune by ear when the sound has strong overtones, noise or a changing pitch envelope.
- Period can provide a starting point for very short resonant delays, but feedback, filtering and interpolation also determine the audible pitch.
- A frequency analyser may show a harmonic more strongly than the fundamental. Confirm that the detected peak represents the pitch you intend to tune.
- Wavelength is an acoustic reference, not a prediction of room modes or speaker response by itself.