Perl itself, is too slow for good audio/visual processing, because of the extra context baggage it places on variables. Your best bet is to use PDL, which will handle the data in Fortran. See PDL::Audio and Manipulating Audio Data in Perl.

My first thought is to read the audio into a audio piddle, with PDL::Audio, then use something like PDL::IO::Pic; to write it to a graphic file, after you tranform the audio piddle to numbers suitable for graphic display. PDL also will do fast FFT for you.

The PDL maillist is very active, and I'm sure that is the best place to look for guidance.