The Sound Glyph shrine was located underneath the Silenced Catherdral. It required 4 points of eldritch energy to use. When cast, Raziel slammed his hands together and an ultrasonic wave would stun all nearby vampires. This glyph merely stunned vampires, humans remained unaffected.
The Sound Glyph was originally intended to be much more powerful, as seen in the Soul Reaver beta versions. Its shockwave actually killed the stunned vampires. This feature is described in the manual but was cut from the retail version of the game.