Several tracks, including "Us and Them" and "Time", demonstrated Richard Wright's and David Gilmour's ability to harmonise their voices. In the 2003 Classic Albums documentary "The Making of The Dark Side of the Moon", Waters attributed this to the fact that their voices sounded extremely similar. To take advantage of this, Parsons used studio techniques such as the double tracking of vocals and guitars, which allowed Gilmour to harmonise with himself. The engineer also made prominent use of flanging and phase shifting effects on vocals and instruments, odd trickery with reverb, and the panning of sounds between channels (most notable in the quadraphonic mix of "On the Run", when the sound of the Hammond B3 organ played through a Leslie speaker rapidly swirls around the listener).