963 Hz is the highest tone in the extended set of Solfeggio frequencies, one of the three, with 174 and 285, added after the original six, and in the sound-healing literature it is associated with the crown centre and with "divine consciousness", unity and the highest spiritual connection, the summit of the ascending ladder of tones.
The Solfeggio frequencies are a modern phenomenon throughout: the core six were assembled by Joseph Puleo in the late twentieth century and popularised from 1999, the fuller nine-tone version later, and the whole set derives from a numerological procedure rather than from any ancient or medieval musical practice, the solfege name notwithstanding, since the medieval scale used no fixed hertz pitch. The arrangement of the tones as a rising series mapped onto the seven chakras joins two separate modern esoteric schemes. There is no scientific evidence for the claimed effects, and nothing in this description constitutes medical advice or a therapeutic claim; it reports the beliefs of a modern sound-healing tradition.
Sources Healing Codes for the Biological ApocalypseLeonard G. Horowitz and Joseph S. Puleo with Claiming Knowledge: Strategies of Epistemology from Theosophy to the New AgeOlav Hammer