400Hz
400 Hz is a frequency that corresponds to four hundred cycles per second. It is a common reference point in audio engineering, where the standard pitch A above middle C (A4) is tuned to 440 Hz. The frequency 400 Hz is slightly lower than this standard, falling in the mid‑range of the audible spectrum for humans.
In music, 400 Hz lies near the middle of the piano’s range, roughly between the notes G3 (196 Hz)
In electronics, 400 Hz is used as a test tone or as a reference in audio equipment calibration.
The frequency is well within the range of human hearing, which spans roughly 20 Hz to 20 kHz for