MATLAB: How can I use bandpass filter on a .wav file

bandpass

Hi, In a project, I am asked to just consider frequency components between 250 HZ and 6000 HZ of a wav file. I tried to use a fir filter as I wrote below but it gave an error. Is there any way to solve this error or is there any different method to just take those frequencies?

if true
  % code
  N = 32;
 fc1 = 250;
 fc2 = 6000;
 B = fir1(N, [fc1 fc2], 'bandpass');
end

Error is : Error using FIR1 Expected Wn to be an array with all of the values < 1.

Best Answer

‘Error using FIR1 Expected Wn to be an array with all of the values < 1.’

The audioread function will return the sampling frequency, ‘Fs’, necessary for you to design your filter.

Try this:

[y,Fs] = audioread(filename)'
Fn = Fs/2;                              % Nyquist Frequency
fc1 = 250/Fn;                           % Normalised Frequency

fc2 = 6000/Fn;                          % Normalised Frequency

Note that ‘Fs’ has to be greater than 12100 for your filter to work well.

I leave the rest to you.

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: How to Butterworth Filter with Bandpass [10 500] with sampling rate 1000

You have to divide your passband and stopband frequencies by the Nyquist frequency to normalise them:

Fs = 1000;                                          % Sampling Frequency
Fn = Fs/2;                                          % Nyquist Frequency
Wp = [10  495]/Fn;                                  % Norrmalised Passband Frequencies
Ws = [5   499]/Fn;                                  % Normalised Stopband Frequencies
Rp =  1;                                            % Passband Ripple (dB)
Rs = 25;                                            % Stopband Ripple (dB)
[n,Wn] = buttord(Wp, Ws, Rp, Rs);                   % Optimal Filter Order
[b,a] = butter(n, Wn);                              % Calculate Filter Coefficients
[sos,g] = tf2sos(b,a);                              % Convert To Second-Order Sections For Stability
figure(1)
freqz(sos, 4096, Fs)                                % Filter Bode Plot

You cannot have any frequency exactly at zero or exactly at the Nyquist frequency, so I designed your passband to be close enough to them to be stable. In your filter, you can also use a high-pass design with a lower cutoff of 10 Hz, since your upper passband is at the Nyquist frequency. The passband and stopband ripple values are necessary to specify in the design but irrelevant to a Butterworth filter. These are acceptable values for most filter designs (for example Chebyshev) that require them.

You would use the ‘sos’ and ‘g’ variables in your actual filter:

filtered_signal = filtfilt(sos, g, signal);

(This design works well in R2016a and should also work in earlier releases.)

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: How to Butterworth Filter with Bandpass [10 500] with sampling rate 1000

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