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07 Feb 2011 (Updated )

This toolbox can be used to design a filter which satisfies prescribed specifications.

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- Filter can be FIR or IIR.
- Filter type can be lowpass, highpass, bandpass, or bandstop.
- Direct methods or optimization ones can be used for the design procedure.

In order to learn how you can use this toolbox, please copy all the codes included in the "Dig_Filter" folder into the current directory of your Matlab and type "help Dig_Filter".

In the case of designing IIR filters using optimization methods, Dig_Filter uses MATLAB functions bfgs, dfp, and inex_lsearch. These functions are part of the MATLAB support materials of the following textbook:

A. Antoniou and W.-S. Lu, "Practical Optimization: Algorithms and
Applications", Springer, 2007

Please see:

These functions can be downloaded from the following Web page:

You can find them here:
MATLAB Algorithm Implementations> Chapter 7> Quasi-Newton Methods

To use these functions, download and copy them in an accessible MATLAB directory, e.g., your current working directory and follow the instructions of Dig_Filter.

To find other Matlab functions about filter design, please visit


This file inspired 2 Dimensional Filter Design Using Mc Clellan Transformation.

Required Products Control System Toolbox
Optimization Toolbox
Signal Processing Toolbox
MATLAB release MATLAB 7.2 (R2006a)
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13 Feb 2011

The cut-off frequencies must be in an increasing order. An error message is added to the toolbox which indicates this problem (in a case that frequencies are not in the right order).

14 Feb 2011

Improvements in the optimization parts.

15 Feb 2011

Copyright Issue

15 Feb 2011

Adding Control System Toolbox as a requirement

16 Feb 2011


17 Feb 2011

Removing 'bfgs','dfp', and 'inex_lsearch'

07 Mar 2011


08 Mar 2011

"bfgs" and "dfp" optimization algorithms.

09 Mar 2011

bfgs, dfp, and inex_lsearch

21 Mar 2011


13 Feb 2012


11 Oct 2012

some changes in comments

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