813Hz

813Hz is a frequency that refers to 813 cycles per second in a sound wave. As a unit of frequency, it is measured in hertz (Hz) and lies within the audible range for humans, which typically spans from about 20Hz to 20,000Hz. In physics, a sound of 813Hz has a wavelength of approximately 0.42 metres in air at standard temperature and pressure, assuming the speed of sound is 343 metres per second. The frequency determines the pitch perceived by listeners: 813Hz is higher than many common musical notes but lower than the pitches used for higher soprano voices and instrumental treble parts.

In music, 813Hz corresponds roughly to the interval of a perfect fourth above the A4 standard tuning pitch of 440Hz, but it is not a tuned pitch in the equal‑temperament system. Musicians sometimes use reference signals or tuning devices set at 813Hz as calibration points in recording studios, especially for headphones and loudspeaker testing, because the frequency is close to the centre of the human hearing spectrum and away from the lower boundary where distortion is often greatest. Audio engineers may use 813Hz in acoustic treatments as a dummy signal to test microphones, preamplifiers, and speaker responses, as it lies in the sweet spot where many transducers operate most efficiently.

There are also alternative medicine and music therapy circles that ascribe specific healing properties to 813Hz. These claims typically lack rigorous scientific validation. The frequency is sometimes listed among a series of “therapeutic” tones such as 432Hz or 528Hz, but mainstream acoustic science recognizes 813Hz simply as a measurable component of audible sound.

Because the human ear is most sensitive around 2,000 to 5,000Hz, 813Hz is less prominent in natural speech and ambient noise, yet it remains an important reference point in a variety of measurement, calibration, and audio production procedures.