Hz

Acoustic Pitch Standard & Microtuning Spectrum Analyzer

ISO A440 vs Verdi A432 & Historic Tuning Acoustics Workbench

Comparison Standard

Custom A4 Frequency (Hz) 432.00 Hz

Synthesizer & Harmonics

Oscillator Waveform

Fundamental Note A4 (440.00 Hz / 432.00 Hz)

Harmonic Overtones 3

Dual Pitch Play (Beat Interference)

Play ISO 440Hz & Comparison simultaneously

Acoustic Physics Environment

Air Temperature (°C) 20.0 °C

Speed of Sound: 343.42 m/s (v = 331.3 + 0.606·T)

Audio Synthesizer Ready

Click Play Synthesizer to unlock real-time Web Audio rendering

Volume

Real-Time FFT Spectrum Peak Analyzer

ISO A=440 Reference

Selected Standard

Oscilloscope Waveform & Beat Interference Envelope

Beat Acoustic Envelope

ISO A440 Baseline Freq

440.00 Hz

λ = 0.7805 m

Comparison Pitch Freq

432.00 Hz

λ = 0.7949 m

Microtone Cents Delta

-31.77 Cents

Δcents = 1200 · log2(f2 / f1)

Acoustic Beat Frequency

8.00 Hz

Modulation f_beat = |f1 - f2|

A440 vs A432: what really changes when you retune

A painted one-minute tour of the analyzer's physics: semitone ratios, cents, beats and wavelength, then the history and sources behind each number.

Read the narration

Why does a song tuned to four thirty-two hertz sound slightly different? This analyzer puts the modern standard, A four forty, side by side with lower historic tunings. Every other note is built from A. Each semitone multiplies the frequency by the twelfth root of two, so retuning A slides the whole keyboard by the same ratio. Musicians measure that slide in cents, a hundred to a semitone. Four thirty-two sits about thirty-two cents below four forty, a third of a semitone. Baroque pitch, four fifteen, is about one semitone lower. Play both A's together and you hear beats. The two waves drift in and out of step, so the loudness swells eight times a second: the difference between four forty and four thirty-two. Temperature changes the wave, not the note. Warm air carries sound faster, so one cycle of A four forty stretches from about seventy-five centimeters at freezing to about eighty-one on a forty degree day. Four forty is simply the shared reference, written into an international standard. Turn on dual play and listen for the beats yourself.

Go deeper

A440 is an agreement, not a law of nature

A 1939 international conference recommended A = 440 Hz. ISO adopted it in 1955 and reaffirmed it in 1975 as ISO 16, which asks for tuning within 0.5 Hz.

Pitch used to vary a lot

France fixed A at 435 Hz in 1859 (the diapason normal). Baroque ensembles today often play at A = 415 Hz, about a semitone below modern pitch. 'Scientific pitch' sets C = 256 Hz, which puts A near 430.54 Hz.

Why no number is 'natural'

Hertz counts cycles per second, and the second is a human-defined unit. A432 is a legitimate tuning choice, but nothing in acoustics makes it more natural than 440.

How big is 32 cents?

An octave is 1,200 cents and a semitone 100. Adults reliably hear a 25-cent difference side by side, and under good conditions people can detect about 5 to 6 cents, so A432 against A440 is clearly audible when compared directly.

Beats are how tuners work by ear

Two tones a few hertz apart swell and fade at a rate equal to their difference. Tuning removes the beats: when the swelling stops, the two pitches match.

Wavelength follows the air

Wavelength equals the speed of sound divided by frequency. The tool uses v = 331.3 + 0.606 × T (m/s, T in °C), so heat changes the wavelength while the pitch you hear stays the same.

Try it in the tool

Turn on Dual Pitch Play with the Verdi 432 Hz comparison and listen for the eight-per-second beating.
Switch the fundamental from A4 to A5: both notes double, and so does the beat rate, to 16 per second.
Choose Baroque 415 Hz: the 25 Hz difference is too fast to hear as separate beats and turns into roughness.
Drag the air temperature slider and watch the wavelengths change while the frequencies stay fixed.

Sources and further reading

ISO 16:1975, Acoustics: Standard tuning frequency (standard musical pitch) · International Organization for Standardization
Sets A = 440 Hz for the note A in the treble stave.
Concert pitch · Wikipedia
History of A440, the 1859 French diapason normal, Baroque pitch, scientific pitch and 'Verdi tuning'.
Cent (music) · Wikipedia
Definition of the cent and research on how small a pitch difference people can hear.
Interference and Beats · The Physics Classroom
Why the beat frequency equals the difference between the two frequencies.
Speed of Sound · NASA Glenn Research Center
How the speed of sound depends on the gas and its temperature.

All numbers in the video come from the analyzer's own formulas: equal temperament from A4, cents = 1200 × log2(f2/f1), beat rate = |f1 − f2|, and the tool's speed-of-sound approximation.

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