(Booklet text of the CD "Portrait Erik Reischl, Volume 4")
The phenomenon of phase shifting was discovered by Steve Reich by mere chance. In 1965 he experimented with spliced audio-tape loops and their psycho-acoustic influence. He recorded a sidewalk evangelist in San Francisco, cut short pieces from this, and then joined them to make audio loops which were played simultaneously on 2 separate tape recorders. Due to minimal differences in the lengths of the loops there was a phase shift of the speech patterns which fascinated the composer. Its Gonna Rain and Come Out resulted as his first tape compositions.
A few months later at the end of 1966, Reich recorded a short piano piece (a pattern), created a loop and then he tried to play against the tape recorder and create a phasing:
"To my surprise, I found that while I lacked the perfection of the machine, I could give a good approximation of it..."
The interesting thing about phasing is the so-called resulting patterns that evolve from the crossing over of these two pieces of music. The human ear seems to unite the phased patterns both melodically and harmonically. This is how in 1967, the work Piano Phase was created and others of its sort followed (including Clapping Music, Violin Phase and Pendulum Music).
In the original composition Piano Phase is written for two pianos. The first piano begins with the pattern of twelve tones and the second piano moves in slowly. Shortly after the second piano speeds up, while the first piano holds strictly to the tempo until he is one note ahead, then he holds the tempo in order to assimilate the resulting pattern. This happens twelve times, until both pianists are back in phase. In a second section Reich introduces a new eight note pattern, to which the second piano plays a pattern which is not the same but similar in harmony and the phasing takes place once again. The four middle tones of this pattern are used for the third and last phase. Again the phasing process takes place and the pianists end together quite abruptly.
This recording is the first in which the composition has been produced by over-dubbing. To begin with I played and recorded the first piano in strict tempo. This recording was then played to me via headphones while I recorded the second piano increasing the tempo during the phasing. Here the recording process returns to the origins of the work.