% bandlimit_audio.m
%
% applies a simple lowpass filter to imported .wav data and saves results back
% into a .wav file


Fs = 44100;             % sampling rate of audio data
N = 705600;             % length of each audio sample
cutoff = 88100;         % cutoff sample for lowpass filter
lowpass = [ones(cutoff,1); zeros(N-(2*cutoff),1); ones(cutoff,1)];

[in_file, in_path] = uigetfile('*.wav', 'Select Audio Input');
[out_file, out_path] = uiputfile('*.wav', 'Select Bandlimited Output File');

disp(['bandlimiting input signal to ' num2str((cutoff*Fs)/N) 'Hz...']);

audio = wavread([in_path in_file],N);     % import test audio

result = ifft(fft(audio) .* [lowpass, lowpass]);     % use simple lowpass filter

disp('plotting bandlimited signal...');
plot(result);

disp('writing bandlimited output file...');
wavwrite(result,Fs,[out_path out_file]);  % write out bandlimited result

disp('done.');