added Petha_Hsu_PitchOffset function

src/Petha_Hsu_PitchOffset.m

@@ -0,0 +1,50 @@
+% 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