[sdiy] Digital Filter is GETTING closer

[Jim Patchell]

Major success tonight.  The four pole filter actually sounds like a four 
pole filter.... (and I have 512 of them...to boot...).  This is more 
filters than I have built in my entire life (well, analog ones that is). 
  Resonance still doesn't work...(doesn't do anything....something isn't 
connected correctly somewhere in the verilog code...).

Putting the four pole filter in sure makes the oscillators sound a whole 
lot better...it band limits them and takes the harshness (aliasing) and 
sort of puts it in it's place...(it is still there, but nowhere near as 
noticeable).

On the XC3S1000 that I am using, I am up to 33% of the logic fabric, and 
21 of the 24 block rams is being used.

I looked at the output with a "logic analyzer" I did, and was very 
impressed to see the waveforms turning gradually sinusoidal and the 
cutoff frequency was lowered.

-Jim
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