AUM is the unstruck sound; there is no instrument. When you become absolutely silent, suddenly it is there. Zen people have the right expression for it; they call it’the sound of one hand clapping’. If two hands are there, of course, the clapping is easy, but one hand clapping and the sound of one hand clapping seems to be absurd — but they are truly expressing the reality. When you go inside and you are absolutely silent you hear for the first time the inner music.