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I need to calculate frequency response, phase response and apply to signals the Butterworth, Chebychev1 and Chebychev2 band-pass filters.

I'm developing in C++ with Qt, and I'm looking for algorithms or a (free) library to do that. I have my plotting solution, I just need the formulas.

The input values I have are the time/amplitude signal, the order of the filter and the low and high cut-off frequencies.

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Do you know what frequency response and phase response are, conceptually? Are you looking for help on the concepts or the implementation? – Phonon Jan 10 '13 at 21:39
Just the implementation, thanks. – gregseth Jan 11 '13 at 7:54

You might try Vincent Falco's Collection of Useful C++ Classes for Digital Signal Processing.

The StackOverflow Question A C++ library for IIR filter offers a few more suggestions.

Finally: the hard part for Butterworth/Chebychev filters is really the design, not the implementation. You might consider doing the design in Matlab (or Gnu Octave), or an online site like: Writing the C code should be trivial once you know the coefficients for the recurrence relation.

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