415 Hz
Baroque (period instruments)
-101.3 cents
Tuning Pitch
415, 435, 440, 442, 443 Hz
430 Hz
Classical era (estimate)
-39.8 cents
435 Hz
French standard pitch, 1859
-19.8 cents
440 Hz
London conference 1939, ISO 16 standard
reference
442 Hz
Common orchestral pitch
+7.9 cents
443 Hz
Some orchestras (Berlin, Vienna)
+11.8 cents
Beats
Two slightly different A's played together produce a pulsation: the number of beats per second equals the difference in hertz. Musicians and tuners use it to adjust their intonation.
Danhauser speaks of “870 vibrations”: a count of single vibrations (one way), that is 435 complete cycles, 435 Hz.
Used in: How the Clefs Relate, Music Notation Around the World