FDAtool - Scale Passband (Chebyshev)

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Jan
Jan 2011-3-24
hello,
In Matlab when I use fdatool i see the option "Scale Passband" now this option changes the coefficients drastically, after some reading I found out the use for it but not the mathematical way to calculate it yourself.
I used for example, fs = 48000hz, fc1 = 4000, fc2 = 6000, order = 4, sidelobe attenuation = 60, scale passband is not checked. That are my FDAtool settings, now I calculated h(0) = 0.917, multiplying h(0) with the window variable (witch comes from chebwin function) gives me 0.917. this value matches FDAtool coefficients, so I can conclude that the coefficients are calculated correctly.
Now when I check the option "Scale Passband" my coefficients change, how they get the new coefficients is for me a complete riddle. Also the chebwin function doesn't calculate the new "scale bandpass" coefficients
Thank you!

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回答（1 个）

Honglei Chen
Honglei Chen 2011-3-24
Hi Jan,
I can't really follow your example but the purpose of scale is to make sure that the center of the first passband has a magnitude response of 1.
HTH.
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Jan
Jan 2011-3-26
Can you give any more mathematical explanation? Maybe a small example?
Honglei Chen
Honglei Chen 2011-3-28
Suppose that using the regular Chebyshev window, you get your coefficients in variable b, and your pass band is centered at f0. Denote B(f0) as the magnitude frequency response of b evaluated at f0, then the scaled coefficients will be
b_scaled = b/B(f0)
Note that B_scaled(f0) = B(f0)/B(f0) = 1.

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