File:G712 butterworth.svg
Summary
| Description |
English: Butterworth filter approximation for CCITT G712 specification |
| Date | |
| Source | Own work |
| Author | Fcorthay |
| SVG development |
Source code
This graphics has been realized with the help of the following Octave script:
#-------------------------------------------------------------------------------
# Specifications
#
fs = 40E3;
fPass = 3000;
rPass = 0.125;
fStop1 = 4000;
rStop1 = 14;
fStop2 = 4600;
rStop2 = 32;
pointNb = 1000;
AdbMin = 40;
makeGraphics = 1;
figureIndex = 0;
#-------------------------------------------------------------------------------
# Denormalized filter function
#
order = 13;
wLog = 2*pi*logspace(2, 5, pointNb);
fc = 0.87;
[num, den] = butter(order, 2*pi, 's');
while ( length(num) < length(den) )
num = [0, num];
endwhile;
for index = 1:order+1
num(index) = num(index) * (fPass/fc)^(index-1);
den(index) = den(index) * (fPass/fc)^(index-1);
endfor
Adb = 20*log10(abs(freqs(num, den, wLog)));
Adb(Adb < -AdbMin) = -AdbMin;
figureIndex = figureIndex+1;
figure(figureIndex);
semilogx(wLog/(2*pi), Adb);
hold on;
semilogx([wLog(1)/(2*pi), fPass, fPass], -[rPass, rPass, AdbMin], 'r');
semilogx([fStop1, fStop1, fStop2, fStop2, wLog(length(wLog))/(2*pi)], ...
-[0 , rStop1, rStop1, rStop2, rStop2 ], 'r');
hold off;
axis([wLog(1)/(2*pi), wLog(length(wLog))/(2*pi), -AdbMin, 0]);
grid;
xlabel('frequency [Hz]');
ylabel('amplitude [dB]');
if (makeGraphics != 0)
print -dsvg g712_butterworth.svg
endif
Licensing
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Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled GNU Free Documentation License. |
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