Analog Filters -> Digital

[Brian Patrick Towles]

sorry, if this is a little off topic.

for a class design project, i've tricked my group into programming a
software vocoder :)  we're going to implement the filterbanks as discrete
bandpass filters - the same way analog vocoders work.  however, none of
the group members knows a good approach to designing these digital
filters.  optimally, we would have a procedure for turning s-domain (
continuous ) filters into z-domain ( discrete ) filters - just because i'm
fairly confident i could design the filterbank using analog filters.

i've read a little about the bilinear-transform, which seems to do
continuous to discrete transformation, but i don't know if that's what we
are looking for ... does anyone have any ideas or algorithms for
converting analog filters into their digital counterparts?

also, before anyone yells "just use fft's", we're aiming for real-time.
i'm fairly convinced that fft's have too much associated delay to work in
this application.  we want real fast, smooth spectral analysis of the
input signal for the optimal vocoding effect.

thanks,

brian

aside: we did an initial presentation of the vocoder, but only mentioned
it's voice compression applications ... hopefully, we'll shock the class
and professor with our final presenation and a chorus of robot voices :)