File:Amplitude & phase vs frequency for 3-term boxcar filter.svg
![File:Amplitude & phase vs frequency for 3-term boxcar filter.svg](https://upload.wikimedia.org/wikipedia/commons/thumb/9/9a/Amplitude_%26_phase_vs_frequency_for_3-term_boxcar_filter.svg/435px-Amplitude_%26_phase_vs_frequency_for_3-term_boxcar_filter.svg.png)
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Summary
DescriptionAmplitude & phase vs frequency for 3-term boxcar filter.svg |
English: These graphs depict the same transfer function as File:Frequency response of 3-term boxcar filter.gif. But here, the amplitude is a signed quantity. And where it is negative, the quantity π has been added to the phase plot (before computing the principal value). The purpose is to illustrate the linear-phase property of the FIR filter.
Русский: Амлитудно-частотная и фазовая характеристики фильтра с конечной импульсной характеристикой скользящего среднего |
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Source | Own work | |||
Author |
original: Bob K vector version: Krishnavedala |
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Permission (Reusing this file) |
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SVG development InfoField | ||||
Python source InfoField | click to expand
This script is a translation of the original Octave script into Python, for the purpose of generating an SVG file to replace the GIF version. import scipy
from scipy import signal
import numpy as np
from matplotlib import pyplot as plt
N = 256
h = np.array([1., 1., 1.]) / 3
H = scipy.fftpack.shift(scipy.fft(h, n=N), np.pi)
w = np.linspace(-N/2, N/2-1, num=N) * 2 * np.pi / N
amplitude = abs(H)
L = int(np.floor(N/6))
negate1 = np.array(range(L)) + 1
negate2 = N - np.array(range(L)) - 1
amplitude[negate1] = -amplitude[negate1]
amplitude[negate2] = -amplitude[negate2]
H[negate1] = -H[negate1]
H[negate2] = -H[negate2]
fig = plt.figure(figsize=[5,5])
plt.subplot(211)
plt.plot(w, amplitude, 'blue')
plt.grid(True)
plt.ylabel('Amplitude')
plt.xlim([-np.pi,np.pi])
plt.xticks([-np.pi, -2*np.pi/3,0,2*np.pi/3,np.pi], [])
plt.subplot(212)
plt.plot(w, np.angle(H), 'blue')
plt.grid(True)
plt.ylabel('Phase (radians)')
plt.xlabel('$\\longleftarrow$ Frequency ($\\omega$) (radians/sample) $\\longrightarrow$')
plt.xticks([-np.pi, -2*np.pi/3,0,2*np.pi/3,np.pi], ['-$\pi$','-2$\pi$/3','0','2$\pi$/3','$\pi$'])
plt.xlim([-np.pi,np.pi])
plt.yticks([-np.pi, -2,-1,0,1,2,np.pi], ['-$\pi$','-2','-1','0','1','2','$\pi$'])
plt.ylim([-np.pi,np.pi])
plt.subplots_adjust(hspace=0.1)
plt.savefig('Amplidue & phase vs frequency response of 3-term boxcar filter.svg', bbox_inches='tight', transparent=True)
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Octave/gnuplot source InfoField | click to expand
This script was derived from the original in order to address some GNUplot bugs: a missing title and two missing axis labels. And to add an Octave print function, which creates an SVG file. Alternatively, the gnuplot screen image has an export function that produces an SVG file, but the π characters aren't as professional-looking. I think the resultant quality produced by this script is now better than the file produced by the Python script.
graphics_toolkit gnuplot
clear all; close all; clc
hfig = figure("position",[100 100 509 509]);
x1 = .12; % left margin for name of Y-variable
x2 = .02; % right margin
y1 = .10; % bottom margin for ticks
y2 = .08; % top margin for title
dy = .08; % vertical space between rows
width = 1-x1-x2;
height= (1-y1-y2-dy)/2; % space allocated for each of 2 rows
x_origin = x1;
y_origin = 1; % start at top of graph area
%=======================================================
N= 256;
h = [1 1 1]/3; % impulse response
H = fftshift(fft(h,N)); % samples of DTFT
abscissa = (-N/2:N/2-1)*2*pi/N; % normalized frequency
% Specify the bins that are to show a negative amplitude
L = floor(N/6);
negate = [1+(0:L) N-(0:L-1)];
amplitude = abs(H);
amplitude(negate) = -amplitude(negate);
H(negate) = -H(negate); % compensate the phase of those bins
phase = angle(H);
%=======================================================
y_origin = y_origin -y2 -height; % position of top row
subplot("position",[x_origin y_origin width height])
plot(abscissa, amplitude, "linewidth", 2);
% Default xaxislocation is "bottom", which is where we want the tick labels.
% set(gca, "xaxislocation", "origin")
hold on
plot(abscissa, zeros(1,N), "color", "black") % draw x-axis
xlim([-pi pi])
ylim([-.4 1.2])
set(gca, "XTick", [-pi -2*pi/3 0 2*pi/3 pi])
set(gca, "YTick", [-.2 0 .2 .4 .6 .8 1])
grid("on")
ylabel("Amplitude")
% set(gca, "ticklabelinterpreter", "tex") % tex is the default
set(gca, "XTickLabel", ['-\pi'; '-2\pi/3'; '0'; '2\pi/3'; '\pi';])
set(gca, "YTickLabel", ['-.2'; '0'; '.2'; '.4'; '.6'; '.8'; '1';])
title("Frequency response of 3-term boxcar filter", "fontsize", 12)
%=======================================================
y_origin = y_origin -dy -height;
subplot("position",[x_origin y_origin width height])
plot(abscissa, phase, "linewidth", 2);
xlim([-pi pi])
ylim([-pi pi])
set(gca, "XTick", [-pi -2*pi/3 0 2*pi/3 pi])
set(gca, "YTick", [-pi -2 -1 0 1 2 pi])
grid("on")
xlabel('\leftarrow Frequency (\omega) (radians/sample) \rightarrow')
ylabel("Phase (radians)")
% set(gca, "ticklabelinterpreter", "tex") % tex is the default
set(gca, "XTickLabel", ['-\pi'; '-2\pi/3'; '0'; '2\pi/3'; '\pi';])
set(gca, "YTickLabel", ['-\pi'; '-2'; '-1'; '0'; '1'; '2'; '\pi';])
% The print function results in nicer-looking "pi" symbols
% than the export function on the GNUPlot figure toolbar.
print(hfig,"-dsvg", "-S509,509","-color", ...
'C:\Users\BobK\Amplitude & phase vs frequency for a 3-term boxcar filter.svg')
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Captions
Items portrayed in this file
depicts
16 August 2017
image/svg+xml
9f3c3a071591f369e4e0d2c300c59f7bdf6e2841
20,378 byte
400 pixel
435 pixel
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Date/Time | Thumbnail | Dimensions | User | Comment | |
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current | 13:04, 1 October 2020 | ![]() | 435 × 400 (20 KB) | commons>Krishnavedala | Text-to-graph aspect ratio renders poorly in thumbnails with text unreadable. |
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Width | 348pt |
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Height | 320pt |