BandPass filter using ellipord

How do I use multiple normalized passband frequencies (Wp) and normalized stopband frequencies (Ws) in the ellipord function to create a bandpass filter? I need to create a bandpass filter using the ellipord function given more than one Wp and Ws. I have more than one of these variables because I have to use the the following frequencies to set the stopband (fs) and passbands (fp); fp1 = 700Hz, fp2 = 4.5kHz, fs1 = 300 Hz, and fs2 = 5.5kHz. The following code I tried does not work since I have to many inputs for the ellipord function:

[X Fs] = audioread('song.mp3');

Gp_b = .9

Gs_b = .01

Fp_b1 = 700

Fp_b2 = 4500

Fs_b1 = 300

Fs_b2 = 5500

Wp_b1 = (2*Fp_b1)/Fs

Ws_b1 = (2*Fs_b1)/Fs

Rp_b = -20*log10(Gp_b)

Rs_b = -20*log10(Gs_b)

Wp_b2 = (2*Fp_b2)/Fs

Ws_b2 = (2*Fs_b2)/Fs

[n_b, Wn_b] = ellipord(Wp_b1,Wp_b2,Ws_b1,Ws_b2,Rp_b,Rs_b)

Error using ellipord

Too many input arguments.

Answer 1

[Star Strider]

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).

[huskies_0223]

Just tried this out and it works, thank you!

[Star Strider]

As always, my pleasure!