Remove unwanted narrowband interference

I have this corrupted audio with the sound of a human lung, and would need to remove its interference.

I have attempted both high pass filter and passband filter, would appreciate if someone can help take a look at my code, and see where I should edit to get a clearer sound.

Corrupted Audio:

https://drive.google.com/file/d/15xrvx8pynmhCd86MY-1Zfc7EmDMv-MwP/view?usp=sharing

My current code:

[y,fs]=audioread('lungaudio.wav'); %y=samples, fs = sampling frequency
Ts=1/fs; %Sampling period

nfft=length(y);
nfft2=2^nextpow2(nfft);

ff=fft(y,nfft2);
fff=ff(1:nfft2/2);

plot(abs(fff));
xfft=fs*(0:nfft2/2-1)/nfft2;

plot(xfft,abs(fff));
xlabel('Frequency/Hz');
ylabel('Normalized Amplitude');
title('Frequency Domain Signal');

fc=550;
[b,a]=butter(6,fc/(fs/2), 'high'); %lowpass filter to only get 60hz
y_filtered=filter(b,a,y);

plot(y_filtered)

% sound(y_filtered,fs);

Graph Obtained:

[Daniel M]

I think you mean to use 'low' in your call to butter.

See this recent question also regarding audio of a lung (perhaps a classmate?)

https://www.mathworks.com/matlabcentral/answers/485744-low-pass-filter-not-working

Answer 1

[Kaashyap Pappu]

Increasing the order of the Butterworth filter could help improve the response. Alternatively, the buttord function can be used to get the optimal order and cutoff frequency values to give to the “butter” function.

Hope this helps!