Maximally flat (maxflat) filters are a special class of FIR filters which have maximally flat passbands and stopbands for the given design parameters. The Maxflat Editoris shown below:

To use the Maxflat Editor:

1. Hit the Sampling Frequency button and specify the sampling frequency.
2. Enter the transition center in the same units as the sampling frequency.
3. Enter the rolloff, either in terms of the number of taps or the maxflat parameter "gamma".  If you enter rolloff in terms of number of taps, the number must be odd.
4. Hit the Design button to generate the filter.  Whichever form of rolloff specification you use, the alternate form will be calculated for you automatically.

Please note that the maxflat design algorithm is very demanding relative to the finite-precision arithmetic used to implement it on a PC.  That can lead to the following problems:

• The design might not converge for certain combinations of transition center and rolloff.
• The filter coefficients tend to rapidly decrease towards zero at each end, leading to very small coefficients.  (They might even show up as zero in ScopeFIR's coefficient editor, or when you export it to a text format.)

Therefore, as a general rule, maxflat filters cannot be designed with more than a few hundred taps.

If the design does not converge, try reducing the rolloff specification and/or changing the transition center.

Once a maxflat filter has been designed, you can analyze its frequency response using the Frequency Response List. If the Automatic option is enabled, ScopeFIR will show you the frequency response at zero (DC), at the Transition Center, and at half the sampling frequency. See Using the Frequency Response List for more information on the Frequency Response List.