The process of composing the phase pieces of Stephen Reich were, according to the composer, discovered by accident while trying to create a spoken canon using dual tape players. What Reich found out was that slowly the two audio tracks would drift apart until it became a reverb, then an echo, then a canon and finally the two would merge again. When I first read about this technique in regards to human performances, my first thought was one of impossibility and I marveled at the musicians (sometimes as many as 18 or more) able to achieve this effect. It reminded me immediately of Cowell and the Rhythmicon and later the pieces which originally Cowell believed were unplayable by human musicians became possible. Today, I attempted this on my own by recording a simple bell loop into Cakewalk Sonar and then trying play with the sound slightly faster, this proved very difficult the first couple of tries, then I managed to achieve a phase shift by playing slightly slower.
The main thing that can be said about Reich’s music since the 1960s is that he has often increased the number of musicians he has used as he has gained more notoriety. The recent composition The Daniel Variations is for a sizeable ensemble with recognizable tonalities and triadic harmonies (as opposed to early tape compositions or percussion pieces that were melodically tonal but did not have any formal harmonic structure). The incorporation of Reich’s music into modern electronic music is notable and his commission of DJ’s to remix his pieces says something about Reich’s view of the viability of contemporary popular music.
To my knowledge, Philip Glass has not employed any phase techniques in his compositions and furthermore it appears as though the music of Glass has always employed a tonal melodic and harmonic foundation without the heavy emphasis on percussion (as is present in the music of Reich). Philip Glass has also contributed greatly to the theatre, film and especially Opera (Einstein on the Beach, Satyagraha and The Beauty and the Beast are three successful Glass operas). Both the music of Philip Glass and Stephen Reich weave long pieces out of very simple melodic or harmonic material but the approach seems to be a fairly different one. Philip Glass’s compositions seem to rely primarily on the chord progression, or chord alternation. In a Glass composition it is not uncommon for there to be two repeated chords and chord arpeggios built off the pattern that go on for an incredibly long time. The music of Reich, more than anything seems to be centered on the melody (especially during his phase pieces) and if harmony is able to come out of the melodic material than all the better, but the pieces are not lesser if no distinguishable harmony emerges.