Extraction the magnitude responce point

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Johan Johan 2020-1-11

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https://ww2.mathworks.cn/matlabcentral/answers/499916-extraction-the-magnitude-responce-point

关闭： MATLAB Answer Bot 2021-8-20

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I have this code matlab

>> w = -pi:pi/500:pi;
>> H = freqz(ones(1,10)/10,1,w);
>> subplot(211)
>> plot(w,abs(H))
>> grid; axis([-pi pi 0 1])
>> ylabel('Magnitude Response')

the design,

If xf=-1 : frequency point , xm : magnitude responce point.

How can i extract the magnitude responce point starting from the frequency point ?

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Meg Noah 2020-1-11

I don't have that version or toolbox to get freqz. I think what you want is to interpolate the abs(H) values for the position of xf=01. It would be something like

xm = interp1(w,abs(H),xf,'pchip');

Sorry, I can't help more. Gotta save my allowance to purchase the newer matlab :-(.

Star Strider 2020-1-11

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Correct!

w = -pi:pi/500:pi;
H = freqz(ones(1,10)/10,1,w);
xm = interp1(w,abs(H),-1);
subplot(211)
plot(w,abs(H))
grid; axis([-pi pi 0 1])
hold on
plot(subplot(2,1,1), [min(w) -1],[1 1]*xm, '-r', [1 1 ]*(-1), [0 xm],'-r')
hold off
text(-1,0,'x_f', 'HorizontalAlignment','center', 'VerticalAlignment','top')
text(min(w),xm,'x_m', 'HorizontalAlignment','right', 'VerticalAlignment','middle')
ylabel('Magnitude Response')