Lie detector prototype (using voice)

clear;

subPlotX = 2;
subPlotY = 1;
recordTime = 1;
L = recordTime * 8000;
frequences = (8000*(0:(L/2))/L)';
tolerance = 5;

% Record Yes
input('Say "Yes" but true')
recorderYes = audiorecorder;
recordblocking(recorderYes, recordTime);
audioYes = getaudiodata(recorderYes);

% FIR Yes
% Reference: https://en.wikipedia.org/wiki/Voice_frequency
filterYes = fir1(100, [300/8000, 3000/8000]);
audioYes = filter(filterYes, 1, audioYes);

% Fourier transform for Yes
Y = fft(audioYes);
L = length(Y);
P2 = abs(Y);
intensityYes = P2(1:L/2+1);
subplot(subPlotX, subPlotY, 1);
plot(frequences, intensityYes);


% Say answer
input('Say Yes or No')
recorderAnswer = audiorecorder;
recordblocking(recorderAnswer, recordTime);
audioAnswer = getaudiodata(recorderAnswer);

% FIR answer
filterAnswer = fir1(100, [300/8000, 3000/8000]);
audioAnswer = filter(filterAnswer, 1, audioAnswer);

% Fourier transform for Answer
Y = fft(audioAnswer);
L = length(Y);
P2 = abs(Y);
intensityAnswer = P2(1:L/2+1);
subplot(subPlotX, subPlotY, 2);
plot(frequences, intensityAnswer);

% Reference: http://luscinia.sourceforge.net/page26/page35/page35.html
meanFrequencyYes = sum(frequences .* intensityYes) / sum(intensityYes);
meanFrequencyAnswer = sum(frequences .* intensityAnswer) / sum(intensityAnswer);


result = meanFrequencyAnswer - meanFrequencyYes
if (meanFrequencyAnswer > meanFrequencyYes + tolerance)
    disp('Lie')
else
    disp('True');
end