Pseg defines a function of time as a breakpoint envelope using the same parameters as Env. These patterns can be used to describe tempo or dynamic variations independent of the rhythmic patterns that express them.
levels 
A Pattern that returns the levels. The first level is the initial value of the envelope, all subsequent values are interpolated.  
durs 
A Pattern that returns segments durations in beats.  
curves 
a Symbol, Float, or an Array of those. Determines the shape of the segments.  
repeats 
a number. The possible values are:

// change a parameter ( Pbind( \note, Pseg( Pseq([1, 5],inf), Pseq([4, 1],inf), \linear), \dur, 0.1 ).play; ) ( Pbind( \freq, Pseg( Pseq([400, 1500], inf), Pseq([4, 4],inf), Pseq([\linear, \exp],inf)), \dur, 0.1 ).play; )