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Merge pull request #14 from ltcptgeneral/petha-hsu-pitchoffset

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add Petha_Hsu_PitchOffset function
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wehsu1 2021-12-05 13:32:19 -08:00 committed by GitHub
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% Petha_Hsu_PitchOffset: input a wave and pitch offset (in percentage)
% This function takes a input sound signal and increases the pitch by the
% offset percentage. The output is not 100% accurate. It is only an
% estimation as the information we the function works with is very limited.
% If 100% output is expected, more information like the frequency and type
% of wave would be required. And the estimation only works for
% f_offset > 0.5. Below 0.5, the output is problematic. Again, the output
% is just a good estimation.
% CONTRIBUTORS:
% Pethaperumal Natarajan: I figured a way to increase the pitch of input
% signal by using fourier transform and shifting the frequency using a for
% loop. Then I used inverse transform to get a sound signal back in the time
% domain.
% Wesley Hsu: I helped solve the problem of being unable to lower frequency
% for the loop using the floor function. This allowed rounding to maintain
% the lower signals that were needed when the code returned the signal back
% into the time domain.
function y = Petha_Hsu_PitchOffset(x, f_offset)
len = length(x);
X = fft(x);
X = fftshift(X); %Fourier transform the input wave
Y = zeros(1, len);
midpoint = len/2;
for i = 1:len
%Shifting the Fourier transform in frequency domain to adjust the
%frequency of signal.
%Floor function is used as signals must be integers and not
%doubles.
if floor((i - midpoint) / f_offset + midpoint) < 1 || floor((i - midpoint) / f_offset + midpoint) > len
continue;
end
Y(i) = X(floor((i - midpoint) / f_offset + midpoint));
end
%Plotted graphs to troubleshoot the problem.
%Fs = 44800;
%f = Fs *(-len/2 : len/2 -1) / len;
%tiledlayout(1,3); nexttile;
%plot(f, abs(X)); title("input"); nexttile;
%plot(f, abs(Y)); title("output"); nexttile;
Y = fftshift(Y);
y = ifft(Y);
y = real(y);
end