There was never one ancient concert pitch. Surviving organs, forks, and written reports put the A above middle C anywhere from below 400 Hz to above 450 Hz depending on the city, the instrument, and the decade. France fixed A=435 by law in 1859, a London conference recommended A=440 in 1939, and ISO published it as ISO 16 in 1975. Nothing in that record shows a universal 432 standard that 440 replaced.

Somebody sends you a clip. Soft synth pad, slow zoom on a cathedral, a voice telling you music used to be tuned to 432 until someone changed it. You've probably seen a version of it. Before we argue with it, it's worth doing the more interesting thing, which is looking at what the instruments themselves say. They kept better records than the comment sections did.

The short version: pitch wandered for centuries, it wandered upward for most of the nineteenth, and 440 won mostly because it was measurable, broadcastable, and close to where a lot of people already were. That's a less cinematic story than a villain flipping a switch. It's also a lot more useful when you're deciding what to do with a master.

Pitch used to be a local fact

For most of musical history, "what is A?" had the same answer as "which organ are we playing with?" Organs were the fixed, expensive anchor in a town, and everything else bent around them. Lynn Cavanagh's short history of how A=440 was established, drawing on Alexander Ellis's nineteenth-century surveys, gives a startling spread for German organs before 1600: from around A=567 Hz on early medieval instruments down to about A=377 Hz around 1511. ISO's own magazine, in Tor Halmrast's "Tune in to ISO 16!" feature (ISO Focus+, Nov.-Dec. 2012), notes that organs in the same city could differ by up to five semitones.

That sounds like chaos, but musicians handled it the way session players handle a capo. They transposed at sight, or composers wrote parts in more than one key. Nobody needed a global number because nobody was trying to make an orchestra in one city sound identical to an orchestra in another on the same night. The need for a standard arrived with travel, printed scores that outlived their towns, and later, radio.

1711: the fork that made pitch portable

The tuning fork is younger than people assume. According to the Whipple Museum at Cambridge, in its brief chronicle of the tuning fork, it was invented in 1711 by John Shore, trumpeter to the English court and a favourite of Handel. Before that, a "standard" pitch usually came from a wooden pitch pipe, which drifted with temperature and humidity. A fork held its note and produced a nearly pure tone. ISO Focus+ puts Shore's fork at A=423.5 Hz.

Sit with that number for a second. The first portable pitch reference we can point to is about 34 cents below 432 and about 66 cents below 440. Around 1800, the article continues, the most common reference was a "Classical pitch" near A=422 Hz, the level often associated with Mozart. Cavanagh, again via Ellis, gives Handel about 423 and Mozart about 422 in modern terms. If you wanted to make a historical argument for a lower A, the documents point you nearer 422 than 432.

The nineteenth-century climb

Then pitch went up, and kept going. The explanation Cavanagh draws from Ellis feels very familiar to anyone who has watched the loudness war: bigger halls wanted more brilliance, wind-instrument makers sold horns pitched a little higher so they'd sound brighter than the competition, and improved strings could be tightened to match. Two forks from the Dresden opera house show the drift in a single building, A=423.2 in 1815 and A=435 by 1826.

London went further. ISO Focus+ describes Philharmonic Society forks stamped at A=433.2 still being sold around 1846, by which time the Society's actual performing pitch had reached a "High Pitch" of about 452.5 Hz. Military bands went higher again, with American military pitch sometimes landing near 457. Singers paid for it. Roles written for a voice at roughly 422 were being sung half a semitone or more higher, and the people with the most to lose started lobbying.

Stuttgart, 1834: where 440 actually starts

Here's the part that tends to get skipped. Johann Heinrich Scheibler, a German silk manufacturer with a serious amateur obsession with acoustics, built a tonometer: a calibrated set of precision forks used with beat counting to measure pitch far more accurately than anyone had managed before. The Whipple Museum credits him with showing that the average concert A of Viennese pianos in the 1830s was 440 Hz, and with having his pitch endorsed in 1834 as a German standard, the so-called Stuttgart pitch. The Concise Oxford Dictionary of Music entry on Scheibler records that he proposed 440 vibrations for A at 69°F.

So 440 is not a twentieth-century invention. It's a nineteenth-century measurement of where good pianos already sat, proposed more than a century before the conference that people like to argue about.

Paris, 1859: 435 by law, and a temperature argument

France moved first on a national rule. In 1859, a government commission fixed the diapason normal at A=435 Hz, defined at a temperature of 15 degrees, as a compromise between the strained high pitches and the older, lower ones. The Whipple chronicle notes that the physicist Jules Lissajous worked on the French standard fork and invented his famous optical calibration method along the way. Other countries gradually followed; ISO Focus+ says Queen Victoria sanctioned the French standard for her private band in 1885.

Britain then did something wonderfully British. Both Cavanagh and ISO Focus+ describe the Philharmonic Society's 1896 decision to adopt A=439 at 68°F, reasoning that the French 435 had been specified at a cooler temperature, so the same instrument in a warmer room would play higher. Cavanagh calls the derivation dubious, and the history of what "15 degrees" originally meant is genuinely tangled. The physics underneath it is real, though, and you can check it.

Broadcasting finishes the job

By the 1930s the problem had changed shape. Radio could put an orchestra in London and one in New York side by side in a listener's living room, and the broadcasting industry pushed hard for one reference. Cavanagh, citing Llewelyn Lloyd's 1949 account, describes an international conference in London in May 1939, with the British Standards Institution handling the arrangements, agreeing on A=440. She also flags a real disagreement in the literature: the New Grove dictionary dates the British endorsement to 1938, which she argues is the same conference with the wrong year.

There's a lovely engineering detail in Lloyd's account. The BBC's tuning note came from a crystal oscillator at one million hertz, divided down to 1,000 Hz, then multiplied by 11 and divided by 25. That gives exactly 440. Because 439 is a prime number, you can't get it that cleanly from a 1,000 Hz base. A practical reason, not a mystical one, nudged the world from 439 to 440.

Across the Atlantic, the U.S. National Institute of Standards and Technology notes in its time and frequency glossary that station WWV has broadcast an A440 tone since 1936. ISO followed with a recommendation in 1955 and then ISO 16:1975, a one-page standard that sets A at 440 Hz and asks that tuning instruments hold it within 0.5 Hz. ISO lists it as last reviewed and confirmed in 2022.

Put every reference on one ruler

Hertz values are hard to feel. Cents aren't. A semitone is 100 cents, and the 440-to-432 move is 1200 × log2(432/440) ≈ −31.77 cents, a ratio of 0.981818. So I wrote a small script that takes the documented references above, converts each one into cents against both 440 and 432, and shows what a 3:30 master would run if you resampled a 440 version to that reference. It also checks the temperature story behind London's 439, and then renders a synthetic tone ladder with ffmpeg and measures every step back out of the file, so you can trust the ruler itself.

#!/usr/bin/env python3
"""pitch_history.py: put historical A4 references on one musical ruler.
Usage: python3 pitch_history.py
Needs: numpy, ffmpeg on PATH.

Part 1 converts documented historical references into cents against
A=440 and A=432, plus what a 3:30 song would run if a 440 master were
resampled to that reference. Part 2 checks the temperature story behind
Britain's 1896 A=439. Part 3 renders a SYNTHETIC pitch ladder with
ffmpeg and measures every tone back out of the file."""
import math, subprocess
import numpy as np

REFS = [  # (label, A4 Hz, source note)
    ("Shore tuning fork, 1711",             423.5, "ISO Focus+ 2012"),
    ("'Classical pitch', c.1800",           422.0, "ISO Focus+ / Cavanagh"),
    ("Dresden opera fork, 1815",            423.2, "ISO Focus+ 2012"),
    ("Dresden opera fork, 1826",            435.0, "ISO Focus+ 2012"),
    ("Stuttgart pitch (Scheibler), 1834",   440.0, "Whipple Museum"),
    ("Philharmonic forks, to 1846",         433.2, "ISO Focus+ 2012"),
    ("London 'High Pitch', c.1846",         452.5, "ISO Focus+ 2012"),
    ("Diapason normal, France 1859",        435.0, "ISO Focus+ / Cavanagh"),
    ("New Philharmonic, London 1896",       439.0, "ISO Focus+ / Cavanagh"),
    ("US military high pitch",              457.0, "ISO Focus+ 2012"),
    ("London conference 1939 / ISO 16",     440.0, "Cavanagh / ISO"),
    ("NY orchestra habit, c.1950 (Mendel)", 444.0, "Cavanagh"),
    ("Cammer-ton grouping (Haynes)",        415.0, "ISO Focus+ 2012"),
    ("Modern 432 alternate",                432.0, "reference"),
]

cents = lambda f, ref: 1200 * math.log2(f / ref)
SONG = 210.0  # a 3:30 master at 440

def mmss(s):
    return f"{int(s // 60)}:{s % 60:05.2f}"

print("PART 1  Historical references on one ruler")
print(f"{'reference':38s} {'A4 Hz':>7s} {'vs 440':>9s} {'vs 432':>9s} {'3:30 resampled':>15s}")
for label, f, _ in sorted(REFS, key=lambda r: r[1]):
    dur = SONG * 440.0 / f
    print(f"{label:38s} {f:7.1f} {cents(f,440):+8.2f}c {cents(f,432):+8.2f}c {mmss(dur):>15s}")
lo, hi = min(r[1] for r in REFS), max(r[1] for r in REFS)
print(f"spread of this list: {lo} to {hi} Hz = {cents(hi,lo):.1f} cents = {cents(hi,lo)/100:.2f} semitones")
print(f"432/440 = {432/440:.6f}  ->  {cents(432,440):+.2f} cents, duration x{440/432:.5f} (+{(440/432-1)*100:.2f}%)")

print("\nPART 2  Temperature and the 1896 A=439")
# 1896 Philharmonic reasoning as reported by Cavanagh (linear 1/1000 per degree F)
lin = 435 + (68 - 59) / 1000 * 435
print(f"Philharmonic linear rule 435 + 9/1000*435      = {lin:.3f} Hz")
# Physics: a pipe's pitch tracks the speed of sound, c ~ sqrt(T in kelvin)
def pipe(f0, t0c, t1c):
    return f0 * math.sqrt((t1c + 273.15) / (t0c + 273.15))
print(f"pipe tuned 435 at 15.0 C, played at 20.0 C     = {pipe(435,15,20):.3f} Hz")
print(f"pipe tuned 435 at 15.0 C, played at 25.0 C     = {pipe(435,15,25):.3f} Hz")
print(f"if '15 degrees' meant Reaumur (18.75 C) -> 20 C = {pipe(435,18.75,20):.3f} Hz")
print(f"cents per degree C near room temp              = {cents(pipe(440,20,21),440):+.2f} c/C")

print("\nPART 3  SYNTHETIC pitch ladder, rendered then measured")
SR, SEG = 48000, 2.0
ladder = [415.0, 422.0, 432.0, 435.0, 440.0, 452.5]
parts = "".join(f"sine=f={f}:r={SR}:d={SEG}[s{i}];" for i, f in enumerate(ladder))
graph = parts + "".join(f"[s{i}]" for i in range(len(ladder))) + f"concat=n={len(ladder)}:v=0:a=1,volume=0.5[out]"
subprocess.run(["ffmpeg", "-v", "error", "-y", "-filter_complex", graph, "-map", "[out]",
                "-c:a", "pcm_s24le", "synthetic_pitch_ladder.wav"], check=True)
raw = subprocess.run(["ffmpeg", "-v", "error", "-i", "synthetic_pitch_ladder.wav", "-f", "f32le", "-ac", "1", "-"],
                     capture_output=True, check=True).stdout
x = np.frombuffer(raw, dtype=np.float32)
n = int(SR * SEG)
for i, f in enumerate(ladder):
    seg = x[i * n + n // 4: i * n + n // 4 + n // 2] * np.hanning(n // 2)
    spec = np.abs(np.fft.rfft(seg, 1 << 20))
    k = int(np.argmax(spec))
    a, b, c = np.log(spec[k - 1:k + 2])
    k_ref = k + 0.5 * (a - c) / (a - 2 * b + c)       # parabolic peak interpolation
    est = k_ref * SR / (1 << 20)
    print(f"rendered {f:6.1f} Hz -> measured {est:8.3f} Hz  (error {est-f:+.3f} Hz, ISO tolerance +/-0.5)")

import os
os.remove("synthetic_pitch_ladder.wav")  # keep the demo folder clean

Here's the real output from running it. The audio in part 3 is synthetic sine tones generated on the spot, not a recording of any instrument.

PART 1  Historical references on one ruler
reference                                A4 Hz    vs 440    vs 432  3:30 resampled
Cammer-ton grouping (Haynes)             415.0  -101.27c   -69.50c         3:42.65
'Classical pitch', c.1800                422.0   -72.31c   -40.55c         3:38.96
Dresden opera fork, 1815                 423.2   -67.40c   -35.63c         3:38.34
Shore tuning fork, 1711                  423.5   -66.17c   -34.40c         3:38.18
Modern 432 alternate                     432.0   -31.77c    +0.00c         3:33.89
Philharmonic forks, to 1846              433.2   -26.96c    +4.80c         3:33.30
Dresden opera fork, 1826                 435.0   -19.79c   +11.98c         3:32.41
Diapason normal, France 1859             435.0   -19.79c   +11.98c         3:32.41
New Philharmonic, London 1896            439.0    -3.94c   +27.83c         3:30.48
Stuttgart pitch (Scheibler), 1834        440.0    +0.00c   +31.77c         3:30.00
London conference 1939 / ISO 16          440.0    +0.00c   +31.77c         3:30.00
NY orchestra habit, c.1950 (Mendel)      444.0   +15.67c   +47.43c         3:28.11
London 'High Pitch', c.1846              452.5   +48.50c   +80.26c         3:24.20
US military high pitch                   457.0   +65.63c   +97.40c         3:22.19
spread of this list: 415.0 to 457.0 Hz = 166.9 cents = 1.67 semitones
432/440 = 0.981818  ->  -31.77 cents, duration x1.01852 (+1.85%)

PART 2  Temperature and the 1896 A=439
Philharmonic linear rule 435 + 9/1000*435      = 438.915 Hz
pipe tuned 435 at 15.0 C, played at 20.0 C     = 438.758 Hz
pipe tuned 435 at 15.0 C, played at 25.0 C     = 442.484 Hz
if '15 degrees' meant Reaumur (18.75 C) -> 20 C = 435.930 Hz
cents per degree C near room temp              = +2.95 c/C

PART 3  SYNTHETIC pitch ladder, rendered then measured
rendered  415.0 Hz -> measured  415.000 Hz  (error -0.000 Hz, ISO tolerance +/-0.5)
rendered  422.0 Hz -> measured  422.000 Hz  (error +0.000 Hz, ISO tolerance +/-0.5)
rendered  432.0 Hz -> measured  432.000 Hz  (error +0.000 Hz, ISO tolerance +/-0.5)
rendered  435.0 Hz -> measured  435.000 Hz  (error -0.000 Hz, ISO tolerance +/-0.5)
rendered  440.0 Hz -> measured  440.000 Hz  (error +0.000 Hz, ISO tolerance +/-0.5)
rendered  452.5 Hz -> measured  452.500 Hz  (error +0.000 Hz, ISO tolerance +/-0.5)

A few things jump out. The references in this short list alone span about 167 cents, more than a semitone and a half. The modern 432 alternate sits between the Classical-era forks and the Philharmonic's 433.2, but it isn't any of them. And the temperature check is the quiet star: a wind pipe tuned to 435 at 15°C plays about 438.8 at 20°C, close to the 439 the British settled on. That's roughly 3 cents per degree near room temperature, which is why organs and oboes were such unreliable anchors and why a steel fork, or a crystal, won.

What the evidence is, and what it isn't

That last column matters. A single fork tells you what one fork was. Forks can be altered, organs get re-pitched, and written reports use different conditions. Historians compare many objects and records and end up with ranges, not a sacred number. Even after 1939, Cavanagh quotes the musicologist Arthur Mendel tuning a continuo organ in New York around 1950 and finding he had to set it near 444 to stay in tune with orchestral players who drifted up from 440. Standards describe an agreement. Musicians are still people with ears and habits.

A standard is a handshake, not a law of music

This is the bit I'd want you to carry into a session. A=440 earned its place by solving coordination problems: instrument makers building compatible products, broadcasters sending a reproducible tone, touring players arriving without surprises, schools teaching from one starting point. None of that makes 440 artistically superior. It just makes it convenient and shared.

Which also means nothing stops you from choosing something else. Period ensembles play at 415 because it suits the instruments and repertoire. Plenty of orchestras sit a little above 440. Producers detune samples, synths, and whole masters for character all the time. A 432 alternate of a finished record is part of that same long habit of moving the reference, as long as you're honest that it's a creative choice and not a restoration of some lost universal pitch.

The working rules are simple. Keep the approved 440 master untouched. Render the alternate from it once, label it clearly, and write down the ratio and method. If you want to understand exactly what that conversion does to a mix, What 432 Hz actually changes in a finished master walks through it, and Resampling, pitch shifting, and tempo change are three different jobs covers why the method changes the runtime. Slowing a record is a close cousin of this, and When to slow the bounce deals with the delivery side of that.

Sources worth reading

• Lynn Cavanagh, "A brief history of the establishment of international standard pitch a=440 hertz" (PDF), drawing on Ellis, Lloyd, and New Grove.
• Tor Halmrast, "Tune in to ISO 16! The long and oscillating history of standard tuning frequency", ISO Focus+, Nov.-Dec. 2012 (PDF).
• Whipple Museum of the History of Science, University of Cambridge, "Historical notes: a brief chronicle of the tuning fork".
• ISO, ISO 16:1975 Acoustics, standard tuning frequency.
• NIST, Time and Frequency from A to Z, entry for A440.

When did A=440 become the standard?

Johann Scheibler proposed 440 in 1834 and it was endorsed at Stuttgart that year. An international conference in London recommended it in 1939, ISO issued a recommendation in 1955, and ISO 16 made it a published standard in 1975.

Was music tuned to 432 Hz before 440?

No single 432 standard appears in the historical record. Surviving forks and organs show references from below 400 to above 450 Hz. The common 'Classical pitch' of about 422 Hz sits roughly 40 cents below 432.

Why did France choose 435 Hz in 1859?

Pitch had been rising and singers were straining. A government commission fixed the diapason normal at 435 Hz as a lower, shared reference, and many institutions outside France later adopted it.

Why do some orchestras tune higher than 440?

A standard coordinates instruments and broadcasts; it does not forbid an ensemble from agreeing on another reference. Many orchestras choose a slightly higher A for brightness and projection, and period groups often use 415.

Does temperature change concert pitch?

Yes for wind instruments and organ pipes, whose pitch follows the speed of sound in the air inside them. Near room temperature that is roughly 3 cents per degree Celsius. A steel tuning fork barely moves.