Lewin's first chapter is an attempt to devise a Generalized Interval System, which in effect, uses basic algebra to organize a given pitch space. Lewin treats each musical space (major key, minor key, ocatonic, 12-tone, etc..) as an individual, unique set of notes to which the same notation can be applied. Diatonic intervals are treated equally regardless of tone and semitone, so in the c-major scale the interval from c to c is O, c to d is 1, c to e is 2, c to f is 3 etc...
 Lewin's notation for intervals is int(s,t) where s and t are pitches in a given system. Therefore, using the above example of Diatonic C major: int(c,c)=0, int(c,d)=1, int(c,e)=2, int(c,f)=3 etc... Given that the pitch space has octave equivalence, this has the effect of working in numeric systems other than base 10. The major scale is base 7, the octatonic is base 8, the pentatonic is base 5 etc.
 The system's first obvious strong point is the ability to equate
spaces. Play or sing the following melodies:
At a glance there is an obvious similarity to the melodic contour, however, the
intervals don't make sense with each other. If we apply Lewin the discrepancies become
clear. Melody a is in C Major, b is in G Octatonic, and c is in D minor. Lewin's interval
formula int(s,t) gives us the following sets of interval class numbers:
One of the nicest things about this system is it eliminates the counterintuitive results that the current system of musical intervals creates. For example a third plus a third equals a fifth (3+3=5!!??). In Lewin's system this example becomes 2+2=4 where int(c,e)=2, int(e,g)=2, and int(c,g)=4.
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