To analyse signals through time then in PureData applying a fourier series FFT or fast fourier transform opens up an array of options to gain access to the frequency content of the signal the time or pitch and the amplitude of the signal.
With this information it is then possible to apply synthesis to the signal and combine this with other aspects of a puredata patch such as MIDI to control and manipulate that content within the patch and externally as Ben Burtt achieves with his work.
Whilst thinking about the vocal content and synthesis options from a sound design perspective,, pausing for thought and putting ideas onto paper is like
thinking of the elements as a patchwork quilt or mind map that interlinks between the functionality. This is all very well thinking on paper, yet what are the fundamental elements or questions that pure data will be needing to consider?