High Pass Filter

%codesrc: https://stackoverflow.com/questions/24195089/remove-noise-from-wav-file-matlab

clearvars; %clear existing variables
close all; %close any open dialogue

fName= 'sentence_with_80hz.wav'; %specify the source file in the working dir
cd 'C:\Users\Ric\Desktop\UNI\Signal II\Assignment' %Navigate to folder containing to audio file
[f,fs] = audioread(fName); %read and sample audio file data

plot(f, 'k');
title('Original Waveform');
xlabel('Time');
ylabel('Amplitude');

%pOrig = audioplayer(f, fs);
%pOrig.play;

%-----Plot the discrete data points of the waveform------

N=size(f,1); %Get the total number of samples
figure; %create figure window
subplot(2,1,1);
stem(1:N, f(:,1),'k'); %plot discrete datapoints
title('Left Channel');
xlabel('Time');
ylabel('Amplitude');
subplot(2,1,2);
stem(1:N, f(:,2),'k'); %plot discrete datapoints
title('Right Channel');
xlabel('Time');
ylabel('Amplitude');
%-------------------------------------------------

%-----Plot the spectrum using Nyquist magic------
df =fs/N;
w=(-(N/2):(N/2)-1)*df;
y=fft(f(:,1), N) / N; %normalising
y2 =fftshift(y); %centre at 0Hz
figure %create figure window
plot(w,abs(y2),'k');
title('Frequency Spectrum');
xlabel('Frequency (Hz)');
ylabel('Amplitude');
%-------------------------------------------------

%--------Filtering--------------------------------

n=7; %order 7 performs best
cutOff = 160 / (fs/2);

%80Hz Noise signal appears to requires twice the freq thanks to the transision band!
[b,a] = butter(n, cutOff, 'high'); %high pass filter to eliminate 80Hz noise signal
freqz(b,a);
fvtool(b,a,'analysis', 'freq');
fOut = filter(b, a, f); %filter the audio using the butter filter coeffients (coef1, coef2, audiodata)

%--------------------------------------------------

%-------------------output-------------------------

plot(fOut, 'k'); %black signal
title('Filtered Waveform');
xlabel('Time');
ylabel('Amplitude');

p = audioplayer(fOut, fs);
p.play;
audiowrite('test.wav', fOut, fs);
%write processes audio to wavfile

%--------------------------------------------------