The solfeggio frequencies are used in sound and meditation practice, each assigned a purpose and often a chakra: 528 Hz, for instance, is widely marketed as a frequency of "transformation" or "love". They are played, toned or used in music by those who hold that particular pitches carry particular healing or spiritual effects.
Joseph Puleo and Leonard Horowitz introduced the set in the late 1990s as six core tones (396, 417, 528, 639, 741 and 852 Hz), which they derived from a numerological reading of a Latin hymn to John the Baptist, from whose lines the medieval solfege syllables (ut, re, mi...) were originally taken. Three more, 174, 285 and 963 Hz, were added later, making the nine the atlas lists.