Usage: FIRdesign [options] fbot ftop ntap

Uses the Remez algorithm to calculate the FIR filter weights
for a bandpass filter; results are written to stdout in an
unadorned (no header) column of numbers.
Inputs are
  fbot = lowest freqency in the pass band.
  ftop = highest frequency in the pass band.
        * 0 <= fbot < ftop <= 0.5/TR
        * Unless the '-TR' option is given, TR=1.
  ntap = Number of filter weights (AKA 'taps') to use.
        * Define df = 1/(ntap*TR) = frequency resolution:
        * Then if fbot < 1.1*df, it will be replaced by 0;
          in other words, a pure lowpass filter.  This change
          is necessary since the duration ntap*TR must be longer
          than 1 full cycle of the lowest frequency (1/fbot) in
          order to filter out slower frequency components.
        * Similarly, if ftop > 0.5/TR-1.1*df, it will be
          replaced by 0.5/TR; in other words, a pure
          highpass filter.
        * If ntap is odd, it will be replaced by ntap+1.
        * ntap must be in the range 8..2000 (inclusive).

 -TR dd          = Set time grid spacing to 'dd' [default is 1.0]
 -band fbot ftop = Alternative way to specify the passband
 -ntap nnn       = Alternative way to specify the number of taps

  FIRdesign 0.01 0.10 180 | 1dplot -stdin
  FIRdesign 0.01 0.10 180 | 1dfft -nodetrend -nfft 512 stdin: - \
            | 1dplot -stdin -xaxis 0:0.5:10:10 -dt 0.001953

The first line plots the filter weights
The second line plots the frequency response (0.001953 = 1/512)

* The Remez algorithm code is written and GPL-ed by Jake Janovetz
* Multiple passbands could be designed this way; let me know if you
  need such an option; a Hilbert transform FIR is also possible
* Don't try to be stupidly clever when using this program