[Fpga-synth] music-dsp list thread about Filterbanks

[Eric Brombaugh]

Magnus Danielson wrote:
> Scott Gravenhorst skrev:
>> Is anyone here watching this? 
>> I'd like to try my hand at this in an FPGA.  Possible?  What would be the
>> minimum size device to try this?
> 
> Depends on what detailed variant of filter you want to use and how many 
> bands. Doable? Probably.
> 
> What topology is it? Give me a pointer!
> 
> IIRs in some smart combination is probably what I would do.

I'm watching that thread too. Coming from a background in wireless 
communications, the first thing I'd try for a filter bank would be some 
sort of transmultiplexer structure:

http://www.google.com/url?sa=t&source=web&ct=res&cd=9&url=http%3A%2F%2Fwww.telfor.rs%2Ftelfor2004%2Fradovi%2FSPS-5-28.PDF&ei=AFgEStLTEZiQmAfP17DlBA&usg=AFQjCNFw9zusG7bxAf1qXeMvcSgcJt0NdA&sig2=zHOG-TfN9IfNmO9GsC9OKw

These are combinations of polyphase FIRs with short FFTs to split a 
signal sampled at Fs into N even subbands at Fs/N sample rate. Put two 
of these back to back with a gain control in between and you could make 
a EQ-like processor. I've got a 16-channel constant bandwidth EQ that 
I've designed in Virtex 5 for my day job that is pretty efficient.

While computationally efficient, the main disadvantage of using 
something like this for audio is that all the bands are the same width, 
rather than increasing bandwidth with frequency as is most commonly 
found in traditional EQs. OTOH, with a sufficiently large number of 
bands you could fake it by ganging bands together at higher frequencies.

Eric