Sound Ledger¹ (Quindar Edition)

Audio culture by the numbers

“Quindar-tones” are the twinned beeps best known from the Apollo and Space Shuttle missions. They’re named for Quindar Electronics, Inc., which produced the related equipment.

50: The difference in Hz between the two tones

2,525 Hz: The higher of the two pitches, in hertz

250ms: The length, in milliseconds, of each of the two tones, individually

I thought to do this entry because someone at some point searched for the word “Quindar” on There was no entry, so I figured I’d make a brief one, and the Sound Ledger seemed like a good format in which to do so.


Quindar-tones resources:,,

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