MATLAB: Filter Butterworth

butterworth

I have this script: Wp=?; Ws=0.6; Rp=?; Rs=?; [n,Wn] = buttord(Wp,Ws,Rp,Rs); [b,a] = butter(n,Wn,'low'); Ws know, how do I choose the Wp,Rp and Rs ? I apologize in advance if the question can be trivial, but I need help. Thank you for your attention and look forward to a reply soon.

Best Answer

It will depend on what you are trying to do (low pass, highpass, band pass, band stop)

You have Ws hence your Wp will change depending on what kind of filter you want. More details about the specificatiosn and examples are given in the documentation

documentation: http://www.mathworks.com/help/toolbox/signal/ref/buttord.html

Wp-Passband corner frequency Wp, the cutoff frequency, is a scalar or a two-element vector with values between 0 and 1, with 1 corresponding to the normalized Nyquist frequency, π radians per sample.

Ws-Stopband corner frequency Ws, is a scalar or a two-element vector with values between 0 and 1, with 1 corresponding to the normalized Nyquist frequency.

Rp-Passband ripple, in decibels. This value is the maximum permissible passband loss in decibels.

Rs-Stopband attenuation, in decibels. This value is the number of decibels the stopband is down from the passband

Related Solutions

MATLAB: How to design FIR lowpass filter with cutoff frequency, fc1 = 20 Hz and FIR bandpass filter with cutoff frequency fc2 = 10 Hz and fc3 = 35 Hz.

Déjà vu

how to design IIR highpass filter with cutoff frequency of 20Hz and FIR bandpass filter with cutoff frequency of 10Hz and 15Hz?

Make the appropriate changes to get the cascaded filter you want.

MATLAB: BandPass filter using ellipord

You are close. The passband and stopband frequencies must be stated as two-element vectors, and normalised by the Nyquist frequency. You can state the passband and stopband ripple (attenuation) values directly as dB, the function assumes they are negative and represent attenuations or ripple magnitudes.

The elliptical filter is an excellent choice.

Try this:

% Fs = 44100;                                                     % Create A Value To Check Code
Fn = Fs/2;                                                      % Nyquist Frequency
Wp = [700  4.5E+3]/Fn;                                          % Normalised Passband Frequencies
Ws = [300  5.5E+3]/Fn;                                          % Normalised Stopband Frequencies
Rp =  1;                                                        % Passband Ripple
Rs = 40;                                                        % Stopband Ripple (Attenuation)
[n_b,Wn_b] = ellipord(Wp, Ws, Rp, Rs)
[z,p,k] = ellip(n_b, Rp, Rs, Wp);                               % Use Z,P,K For Precision
[sos, g] = zp2sos(z, p, k);                                     % Use Second-Order Sections For Stability
figure
freqz(sos, 2^14, Fs)                                            % View Filter Bode Plot
X_Filtered = filtfilt(sos, g, X);                               % Filter Signal

Use the value for ‘Fs’ that your audioread call returns. I used the commented-out value to check my code to be sure it works (no typographical or other errors).

Best Answer

Related Solutions

MATLAB: How to design FIR lowpass filter with cutoff frequency, fc1 = 20 Hz and FIR bandpass filter with cutoff frequency fc2 = 10 Hz and fc3 = 35 Hz.

MATLAB: BandPass filter using ellipord

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