[sdiy] Starting a Four Pole Filter in an FPGA.....

Jim Patchell patchell at cox.net
Sun Nov 2 17:45:49 CET 2008

Thanks for the links...if nothing else...they are both very 
interesting...and hopefully, I will find something very useful at one of 
those....the musicdsp site looks particularly good...


ASSI wrote:
> On Sonntag 02 November 2008, Jim Patchell wrote:
>> I am just now starting to implement the four pole filters that I am
>> going to attempt to get into my FPGA based synth...
>> I am still trying to figure out the pipe-lining...which is probably
>> the most difficult part of the whole thing.
> The difficult part is coming up with a suitable filter topology.  I 
> guess you'll be doing bit-parallel integer arithmetic.  Then it is 
> problematic to use biquads - they are going unstable at low cutoffs 
> (unless you put in extra precision) due to quantization errors.  
> State variable wacks out at high frequency depending on Q and 
> therefore requires oversampling.  A few pointers:
> http://www.earlevel.com/Digital%20Audio/index.html
> http://www.musicdsp.org/archive.php?classid=3 (mostly FP code)
> Other than that I'm afraid I won't be of much help, it simply has been 
> too many years since I've been doing real DSP myself...
> Achim.

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