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juha_p
KVRist
 
455 posts since 21 Feb, 2006, from FI

Postby juha_p; Fri Jun 01, 2018 5:18 am Adjust gain, analog model of LP filter

I have this "analog model" of one pole LP filter:

Code: Select all
w0 = 2*pi*fc;
b = 1;
a = [1 w0];


I would like to drop the filter say -3dB ... is it OK to do by just multiplying the transfer result?

Example (Octave code, fc = 700Hz):

Code: Select all
G = 1/sqrt(2);
AnalogLP1 = tf(b, a);

% Results:
% Transfer function 'Analog' from input 'u1' to output ...
%
%         1
% y1:  --------
%     s + 4398
%
%Continuous-time model.
%
% without gain normalization filter is at -72.866 dB

AnalogLP1 = AnalogLP1 * a(2) * G

%Results:
% Transfer function 'Analog' from input 'u1' to output ...
%        3110
% y1:  --------
%     s + 4398
%
%Continuous-time model.
%
Ivan_C
KVRian
 
1060 posts since 11 Aug, 2004, from Marcoussis, France

Postby Ivan_C; Fri Jun 01, 2018 7:37 am Re: Adjust gain, analog model of LP filter

If you multiply your analog transfer function with a constant, you get a new transfer function which is absolutely the same but with the magnitude amplified or attenuated by that constant for every frequency...
juha_p
KVRist
 
455 posts since 21 Feb, 2006, from FI

Postby juha_p; Fri Jun 01, 2018 8:57 am Re: Adjust gain, analog model of LP filter

Thanks for the info.

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