Phase Vocoder   

The phase vocoder is an effective tool for the manipulation of the duration or the pitch of a sound file. Each of these transformations may be made independent of one another meaning pitch may be changed without changing the duration, duration without changing pitch. 
The phase vocoder works by performing an FFT analysis of the sound and "reconstructing" the sound as a set of sine waves. These sine waves can then be manipulated to stretch or shift the sound in certain specified ways. 

The Phase Vocoder window in SoundHack provides a number of options aside from the basic degree of duration/pitch change. 

one to six 
by Philip Glass
  one to six 
using SoundHack phase vocoder. Using
"Pitch Scale" and the scaling function 
below produced this sound example.
  Bands allows the choice of the number of bands used in the analysis/resynthesis. The higher the number, the higher the fidelity. The compromise is, the higher the number, the longer the processing time. It is advisable to pick a number between 512-2048. 

Overlap allows the selection of frame overlap. Selecting a higher overlap (4) will result in a delay type sound resulting from the overlap of the bands. 

Window allows the selection of different window types. Each of these will alter the sound slightly and are worth trying out. 

Scaling allows for the illustration of a waveform to be used as a function for the process itself. This allows for "dynamic" time stretches or pitch changes. 

 Resynthesis gating allows for the input of amplitude parameters of the output sound so that amplitude may be controlled to some degree.