How to filter and FFT raw data

Can someone help me with the matlab code:

I have a raw data (attached) from acoustic sensor. I want to filter the signal and carry out fft then plot the graph.

Answer 1

[Star Strider]

I am not certain what you want to do.

One approach:

D = load('exp 8b.txt');
t = D(:,1);
s = D(:,2);

figure
plot(t, s)
grid
title('Original Signal')
xlabel('Time')
ylabel('Amplitude')

sm = mean(s);
L = size(D,1);
Ts = mean(diff(t));
Fs = 1/Ts;
Fn = Fs/2;
FTs = fft(s-sm)/L;
Fv = linspace(0, 1, fix(L/2)+1)*Fn;
Iv = 1:numel(Fv);

figure
plot(Fv, abs(FTs(Iv))*2)
grid
title('Original Signal')
xlabel('Frequency')
ylabel('Amplitude')

sdn = wdenoise(s);                                  % Denoise (Wavelet Toolbox)
figure
plot(t, sdn)
grid
title('Denoised Signal')
xlabel('Time')
ylabel('Amplitude')

Wp = [859 862]/Fn;                                  % Passband Normalised
Ws = [855 865]/Fn;                                  % Stopband Normalised
Rp =  1;                                            % Passband Ripple (Irrelevant in Butterworth)
Rs = 50;                                            % Stopband Attenuation
[n,Wp] = ellipord(Wp,Ws,Rp,Rs);                     % Order Calculation
[z,p,k] = ellip(n,Rp,Rs,Wp);                        % Zero-Pole-Gain 
[sos,g] = zp2sos(z,p,k);                            % Second-Order Section For Stability

figure
freqz(sos, 2^16, Fs)                                % Filter Bode Plot

s_filt = filtfilt(sos, g, s);                       % Filter Signal

figure
plot(t, s_filt)
grid
title('Filtered Signal')
xlabel('Time')
ylabel('Amplitude')

s_filt = filtfilt(sos, g, sdn);                       % Filter Denoised Signal

figure
plot(t, s_filt)
grid
title('Filtered Denoised Signal')
xlabel('Time')
ylabel('Amplitude')

Your signal has significant broadband noise, and a wavelet denoising step is the only way to deal with that. See the documentation for wdenoise (R2017b and later releases) for details on the function.

There appears to be a frequency peak at about 861 Hz, and the bandpass filter here selectively (and efficiently) filters the region from 859 Hz to 862 Hz.

Expertiment to get the result you want.

[Peter Odedeyi]

Thanks so much star strider it worked!. Indeed you are a star. Hope i can always call upon you.

[Star Strider]

As always, my pleasure!

Of course you can!