About FirFilterDesigner

FIR Filter designer is a program that designs Finite Impule Response (FIR) Filters.

This program produces filter files, i.e. documents, with the file extention ".fir". These are binary files that store all filter parameters and all parameters needed to render a C/C++ header file that defines an array with the filter coefficients. The header file will have the same file name as the filter file, but with the file extension ".h". Once a document is assigned a name, any changes to the filter are saved to the file automatically. A loaded filter document can be copied to another empty document using the "Filter" menu item and selecting the "Copy" submenu item.

There are no automatic adjustments to frequencies or settings. What the user enters is what is used to create the filter. This had the advantage of allowing a simple interface, and allows more flexible designs. The disadvantages are all frequencies, transition widths, the filter lengths must be explicitly adjusted by the user.

Filter Design Methods

This program produces only certain types of FIR filters.

• The Parks-McClellan FIR Filter Design method supports Multiband FIR filter design, Differentiator FIR filter design, and Hilbert Transformer FIR filter design.

  The Parks-McClellan designer allows specifying a filter lengths from 3 to 512, however, I've never seen this specific implementation converge to a solution beyond a filter length of 387.

  The Parks-McClellan algorithm won't always converge. If the Parks-McClellan algorithm does converge, it will usually produce the best filter design, that is, a filter with the smallest transition widths and/or the lowest filter length for a given frequency specification. If it fails for a particular design even after tweaking transition widths and the filter length, then one of the next two filter design methods can be used.

• This Frequency-Sampling FIR Filter Design method implementation only supports designing Type 1 odd length multiband FIR filters. If an even filter length is specified, the filter length will be decremented by one.
• The Window FIR Filter Design method supports creating only Lowpass, Highpass, Bandpass, and Bandstop filters.

The Filter Response Graph

The FIRFilterDesigner Graph displays the filter frequency response. Optionally, the phase response of the filter can also be displayed.