440 Hz Tone Generator

440 Hz is the A above middle C, and it is the number almost every piece of recorded music since the middle of the twentieth century is built around. The generator below is set to it. This page covers how a single frequency became the reference for an entire industry, what the standard actually says, and why plenty of orchestras still ignore it.

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How A=440 became the standard

Before standardisation, pitch was local. A church organ in one German town could be a whole tone away from the one in the next, and concert pitch rose steadily through the nineteenth century as orchestras chased a brighter sound, which wore out singers. France legislated A=435 Hz in 1859. Britain and the United States drifted higher. Johann Scheibler had already proposed 440 in 1834, after measuring pitches with a set of tuning forks.

The modern figure was fixed at a conference in London in 1939, where the International Federation of the National Standardizing Associations recommended A=440 Hz. The Second World War delayed adoption. The International Organization for Standardization issued it as Recommendation R 16 in 1955 and reaffirmed it as ISO 16 in 1975, which is the document usually cited today.

What ISO 16 does and does not say

ISO 16 is one of the shortest standards in existence. It states that the note A in the treble clef shall have a frequency of 440 Hz, and that the measurement applies at 20 degrees Celsius once an instrument has settled. That is essentially the whole content. It says nothing about temperament, it names no permitted deviation, and nothing enforces it.

So 440 Hz is a reference, not a rule. Manufacturers build to it, tuning software starts there, and recorded music sits overwhelmingly at or very near it, which is why it is the useful number when you tune to a track. Historical performance ignores it deliberately: baroque ensembles commonly use A=415 Hz, almost exactly a semitone lower, and classical period groups often sit around 430.

Why orchestras still play sharp of 440

Concert pitch in Europe has crept up again. Many German and Austrian orchestras tune to 443 Hz, the Vienna Philharmonic among them, and 442 is common across the continent. British and American orchestras usually sit between 440 and 442. The reasoning is a brighter, more projecting string sound, and once one group moves up, the rest follow to stay with it.

The gap is small but audible. 443 Hz is about 12 cents above 440, roughly an eighth of a semitone, which is enough to beat noticeably against a fixed pitch instrument. That is why a visiting soloist asks what the orchestra tunes to, why an organ or a harp constrains the choice, and why an oboe rather than a machine still gives the A in most halls.

Using 440 Hz as a tuning reference

To tune by ear, play the tone and sound your A against it. Two pitches close together produce a beat, a slow pulsing in loudness; the beat slows as you approach the target and disappears when you arrive. Tuning by beats is more accurate than tuning by whether two notes sound the same, because the ear resolves rhythm more finely than it resolves small pitch differences.

For a whole instrument the microphone tuner is faster: it reads every string in cents instead of making you count beats, and the reference moves between 415 and 466 Hz if you are matching an orchestra at 442. Use this page when you want a fixed reference in the room instead, for a group of singers, for checking a tuning app against something known, or for tuning without a microphone.

Where to go next

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