Om tuning fork — 136.10 Hz

Of all the forks in the set, this is the one used most often: sessions open and close with it, and almost every interval in Acutonics is Om plus something else. The practical reason is simple: the tone is low and calm, and it does not grate on the ear even after a long time.

This, by the way, is where the famous “432 Hz” comes from. If you work out the tuning in which 136.10 Hz would be an exact C sharp, you get A = 432.1 Hz. There is nothing mystical about it: it simply follows from the fact that the Earth year does not divide evenly into twelve semitones. Historically, though, the “432 tuning” and the “Earth tone” are connected precisely through this number.

Oddly enough, there are three kinds of year, and they give slightly different frequencies. Cousto uses the tropical year, the year of the changing seasons; the sidereal year, measured against the stars, would give 136.0969 Hz, and the Julian year, the conventional 365.25 days astronomers use to measure long periods, 136.0993 Hz. The gaps are thousandths of a hertz and cannot be heard, and even in tables rounded to the hundredth all three years give the same 136.10.

This is a system of correspondences, not the result of a measurement: controlled studies of planetary frequencies do not exist. We present the tradition because it exists and the practice is built on it — but we call it tradition.