While there are many ways to link the zodiac to sound, Birth-Tone uses a system called
“The Astronomical Scale” created by Roel Hollander. The Astrological Zodiac divides the calendar year into 12 parts. Each part correlates with the 12-Tone Equal Temperament. However, because the zodiacal constellations (i.e. signs) vary in size and shape, each of the 12 intervals vary in size/length. The data used for the length of each of these intervals was calculated by Juan Anthony Revilla and Pierre Bacchus in “L’Astronomie” (1979). With that data, you can assign a tone-span (1200 cents) to each interval. For example, the date span for the constellation “Aries” is 25.48 days which converts to 83.710317225 cents. Birth-Tone begins at 256Hz (Scientific Pitch) and then increases in frequency based on the tone-span value between each interval.