What sonic artifacts are caused by phase vocoders? When using a phase vocoder to alter the spectral envelope of a signal, the input signal is split up into many (often hundreds of) bands. With many phase vocoders, the output levels these individual bands are often controllable by the user.


What artifacts are caused by filtering these individual bands in a phase vocoder?
If and why, phase vocoders are better suited (and cause less artifacts) than FIR filters (or other methods) for surgical changes to such narrow frequency bands.  For example, are phase vocoders going to cause the same, or less, pass band ´ringing´ than using an FIR filter for the same task?


I understand phase vocoders only up to the point that they use an inverse DFT to resynthesise the sound, though Im not sure exactly how the individual bands are resynthesized, so I dont know what the problems/artifacts will be.
The term "phase vocoder" may encompass more than one resynthesis method.  One method uses a pruned frequency reassignment of the DFT basis vectors, and thus resynthesizes sound using a sparser set of basis vectors with slightly different frequencies than were present in the original DFT analysis windows.

This sparse basis may not be able to recreate a full spectrum wide-band signal, such as produced by a transient, as well as the original non-reassigned full DFT basis.  

Phase vocoder analysis also makes the assumption that the spectrum is fairly stationary between FFT frames, an assumption that can also be violated by transients.  

One term for the artifacts produced by this type of analysis/resynthesis is transient smearing.