## IRR Filter desighn

Scope and XITE Development

Original topic on PlanetZ: https://forums.scopeusers.com/viewtopic.php?t=31946

#### IRR Filter desighn

Posted: Fri May 03, 2013 11:09 am
by earth
hey you guys
can someone please upload a scheme of a filter made only with
add and multyply components ... Not an already build module
http://en.wikipedia.org/wiki/File:IIRFilter2.svg
i need to ilustrate a real dsp engine with the z transform
and make it work
i need your imidit help
thnx

#### Re: IRR Filter desighn

Posted: Fri May 03, 2013 12:07 pm
by jksuperstar
This sounds like a homework problem. And you should read a bit more on IIR filters, because the picture you chose is a poor example...there are no coefficients to tweak (ie - no multiply or scaling!!)
Read this:
http://www.eas.uccs.edu/wickert/ece2610 ... _chap8.pdf
Then go to page 8-13. Then work you're way through the direct form I, into form II (reduced memory elements (Z^-1)), and finally a few pages later, the transposed Direct Form II (reduced summing points). Those diagrams are an exact layout of how you'd connect things in modular.
The only tips you need to do them are these:
Z^-1 == Feedback module (1 sample delay)
Multiply == VCA with constant used for coefficients.
Add == 2 input Mixer with both inputs set to 12 o'clock.
The other tick, is in calculating the coefficients a0, a1, b0, b1 and so on!

#### Re: IRR Filter desighn

Posted: Fri May 03, 2013 12:52 pm
by earth
can i use the math moudules ???
add is add ...
etc,,,

#### Re: IRR Filter desighn

Posted: Fri May 03, 2013 1:32 pm
by jksuperstar
sure, and there's other ways to do multiply. But I do think the feedback module is the guaranteed way to get 1 sample delay.

#### Re: IRR Filter desighn

Posted: Sat May 04, 2013 5:55 am
by earth
fir is more relevant ..
does the frequency changes through the coefficients ???

#### Re: IRR Filter desighn

Posted: Wed May 08, 2013 2:34 am
by Roland Kuit
I made a few IRR filters. Even one with a complete matrix.
The FB module is needed but doesn't give you the 1-sample Delay.
You need the Flexor Sample Delay module for that.
On the other hand, the Flexor Sample Delay module can't be used as a feedback module.

#### Re: IRR Filter desighn

Posted: Wed May 08, 2013 5:23 am
by tgstgs
the feedback IS a 1 sample delay_
good vibes

#### Re: IRR Filter desighn

Posted: Wed May 08, 2013 6:21 am
by Roland Kuit
Thank you tgstgs .
That's why I mentioned the Flexor Sample Delay module in specific.
I was wondering why it cannot be used as a Feedback module.
Any ideas?

#### Re: IRR Filter desighn

Posted: Fri May 10, 2013 1:47 am
by tgstgs
it is 1 object;
the algo checking to protect for recursion without delay doesnt know that it is a delay_
how could he;
good vibes

#### Re: IRR Filter desighn

Posted: Fri May 10, 2013 7:04 am
by jksuperstar
Ahhhh, that is really good to know, and I am glad (or lucky) not to have run into that problem!
Thanks!

#### Re: IRR Filter desighn

Posted: Sat May 11, 2013 12:29 am
by tgstgs
heres a 1 tap sitting in PM // no feedback
im a feedforward freak you know
good vibes

Attachments
  tgsds1tap.zip
    (1.32 KiB) Downloaded 169 times

#### Re: IRR Filter desighn

Posted: Sat May 11, 2013 12:33 am
by tgstgs
with sdk look into the feedback modul to see how they fool their algo_

#### Re: IRR Filter desighn

Posted: Mon Aug 05, 2013 11:43 am
by Roland Kuit
Happy feedfoward! Thanks!

#### Re: IRR Filter desighn

Posted: Tue Aug 06, 2013 1:19 pm
by Roland Kuit
With compliments to tgstgs modules:
A Schroeders All pass filter

Attachments
  Schroeders Allpass.rar
    (4.01 KiB) Downloaded 157 times
    Roland Kuit Schroeders Allpass.jpg (55.42 KiB) Viewed 4603 times

#### Re: IRR Filter desighn

Posted: Tue Aug 06, 2013 1:41 pm
by sharc
Looks good Roland

#### Re: IRR Filter desighn

Posted: Tue Aug 06, 2013 2:06 pm
by Roland Kuit
Thanks Shark, but I have to test the mixers. In this case they must be linear.
Tomorrow an other day.

#### Re: IRR Filter desighn

Posted: Wed Aug 07, 2013 1:09 am
by jhulk
yes looks good roland