# FIR Low Pass Filter Coefficient Generator Octave Script
# Copyright D-TACQ Solutions 2005
# uses the remez FIR filter algorith from octave-forge 
# 15th August May 2005
# Written by John McLean
function filtergen132( ncoeffs, pb1, sb1, samplerate )
# ncoeffs - number of coefficients + 1 
# pb1 - pass band corner, kHz
# sb1 - stop band start, kHz
# samplerate kHz [default=32000]

if (nargin < 4)
	samplerate=32000;
	if (nargin < 3)
		printf("filtergen132( ncoeffs, pb1, sb1, samplerate )\n");
		return
	endif
endif

# now do the  filters
#setup the Fequency characteristic
nyquist = samplerate/2;
f = [0 pb1/nyquist sb1/nyquist 1];
#setup the gain / roll-off
a = [1 1 0 0];
#calculate the coefficients
b1 = remez(ncoeffs,f,a);
# scale the output
tot=sum(b1);
b1 = b1/tot;
[h1,w1] = freqz(b1,1,512);
#plot(f,a,w/pi,abs(h));
freq = w1/pi * nyquist;
for x=1:512
	amp = abs(h1(x));
	logamp1(x) = 20 * log10(amp);
endfor
title1 = sprintf("FIR Low Pass Filter Design Remez Implementation of Parks-McClellan \n");
title2 = sprintf("Passband = %dkHz, Stopband = %dkHz, Samplerate %dkSPS with %d coefficients\n",pb1,sb1,samplerate,ncoeffs-1);
thetitle = strcat(title1,title2);
plot(freq,logamp1);
title(thetitle);
grid("on");
#gset timestamp;
axis ([0,nyquist,-100,1]);
xlabel ("Frequency (kHz)");
ylabel ("Amplitude (dB)");
#legend('No Filter','Boxcar','Filter3','Filter4','Filter5','Filter6','Filter7','Filter8');
# save off the Filter Coefficients.
#scale the data to 18 bit coefficients
b1 = 131071 * b1;
#datafile = strcat(filename,datafile);
datafile = "FIR_132.coe";
myfile=fopen( datafile, "w" );
fprintf( myfile, "radix=10;\n");
#fprintf( myfile, "coefdata=");
fprintf( myfile, "coefdata=%d",b1(2));
for x=3:ncoeffs;
fprintf( myfile, ",%d",b1(x));
endfor
fclose( myfile );
filename=sprintf("acq132filter_%dtaps_%dkHz_%dkHz_%d_kHz",ncoeffs,pb1,sb1,samplerate);
psfile = strcat(filename,".ps");
outfilecommand = sprintf("print -dpsc2 -landscape  \"%s\"",psfile);
#printf("%s \n",outfilecommand); 
eval(outfilecommand);