KJBob

The Nth Order Filter

Discussion created by KJBob on Aug 30, 2015

     This filter has shown up unceremoniously in recent SigmaStudio betas, and it's immensely useful.

 

     Previously, to make a sharp filter we had to cascade a number of first and second-order sections,  Their frequency and Q had to be figured with a filter-design program.  Now, SigmaStudio does the work for you.  Below are two 4 KHz "brick wall" Chebyshev telephone filters, done the old way and the new way:

 

Filter-sch.png

 

     The Order number N (number of poles in the filter) must be even.  If you change N with the green button, it chooses even numbers.  You can go ahead and type an odd number in the box, but the resulting response is incorrect.  Thus I'm comparing a 12-pole Nth-Order filter to an 11-pole assembled filter.  Here the Nth-Order filter uses three more instructions (60 instead of 57), but works much better as shown below:

 

Filter-resp.png

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