[sdiy] Digital 4 pole filter in an FPGA

[Jim Patchell]

I have been doing digital design since about 1975...using FPGAs is just 
another phase of doing the same thing...instead of using 74xxx 
logic...now I write in verilog.  There are a lot of books on Amazon.com 
that cover this subject...although, I wouldn't really know which one 
would be the best to begin with.

And FPGA synths are a lot of fun...and there are more ways to skin this 
cat than you can shake a leg at...

-Jim

HL-SDK Synths wrote:
> I'm interested as well, I have a question though, where did you learn 
> all of this FPGA ...stuff? I've looked around on the web and I'm no 
> computer science guy. Is it all hidden in the textbooks? I think FPGA 
> synths are crazy cool!
> 
> On Tue, Dec 9, 2008 at 12:09 AM, Jim Patchell <patchell at cox.net 
> <mailto:patchell at cox.net>> wrote:
> 
>     Hope y'all aren't getting tired of these progress reports.
> 
>     But it looks like I have got the basics of the four pole filter
>     working (at least in the simulator).  It is going to take a bit more
>     testing to verify that all of the data is going where and when it is
>     supposed to...
> 
>     The filter has a four clock pipe delay through it...i.e. it takes
>     four clock cycles to complete one sample...but since it is
>     pipelined...it only takes 512 clocks to complete all 512 filters...
> 
>     One of the things I need to verify yet is that the resonance control
>     works as it should.
> 
>     Now, also to give you an idea of exactly what I am doing, this is
>     basically the same kind of filter you would make with an
>     SSM2040...without, unfortunately, the non-linear distortion that is
>     inherent in the SSM2040.  I am not sure if I will be able to add a
>     non-linearity in the filter loop or not.  That may be some future
>     experiment.
> 
>     Anyway...it is sure looking promising.
> 
>     -Jim
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