Harmonic product spectrum Matlab coding error - matlab

Question

I'm trying to find the fundamental frequencies present in a piano recording using MATLAB. These are the steps I've followed;
Find the envelop of the signal
Find the note onsets
perform FFT between each onset
Harmonic product spectrum.
It's when I try to implement the HPS algorithm that I face a "dimensions don't agree" error. This is the whole code that I've used.
[song,FS] = wavread('C major.wav');
%sound(song,FS);
P = 20000;
N=length(song); % length of song
t=0:1/FS:(N-1)/FS; % define time period
song = sum(song,2);
song=abs(song);
% Plot time domain signal
figure(1);
subplot(2,1,1)
plot(t,3*song)
title('Wave File')
ylabel('Amplitude')
xlabel('Length (in seconds)')
%ylim([-1.1 1.1])
xlim([0 N/FS])
%----------------------Finding the envelope of the signal-----------------%
% Gaussian Filter
x = linspace( -1, 1, P); % create a vector of P values between -1 and 1 inclusive
sigma = 0.335; % standard deviation used in Gaussian formula
myFilter = -x .* exp( -(x.^2)/(2*sigma.^2)); % compute first derivative, but leave constants out
myFilter = myFilter / sum( abs( myFilter ) ); % normalize
% Plot Gaussian Filter
subplot(2,1,2)
plot(myFilter)
title('Edge Detection Filter')
% fft convolution
myFilter = myFilter(:); % create a column vector
song(length(song)+length(myFilter)-1) = 0; %zero pad song
myFilter(length(song)) = 0; %zero pad myFilter
edges =ifft(fft(song).*fft(myFilter));
tedges=edges(P:N+P-1); % shift by P/2 so peaks line up w/ edges
tedges=tedges/max(abs(tedges)); % normalize
%---------------------------Onset Detection-------------------------------%
% Finding peaks
maxtab = [];
mintab = [];
x = (1:length(tedges));
min1 = Inf;
max1 = -Inf;
min_pos = NaN;
max_pos = NaN;
lookformax = 1;
for i=1:length(tedges)
peak = tedges(i:i);
if peak > max1,
max1 = peak;
max_pos = x(i);
end
if peak < min1,
min1 = peak;
min_pos = x(i);
end
if lookformax
if peak < max1-0.001
maxtab = [maxtab ; max_pos max1];
min1 = peak;
min_pos = x(i);
lookformax = 0;
end
else
if peak > min1+0.005
mintab = [mintab ; min_pos min1];
max1 = peak;
max_pos = x(i);
lookformax = 1;
end
end
end
% % Plot song filtered with edge detector
figure(2)
plot(1/FS:1/FS:N/FS,tedges)
title('Song Filtered With Edge Detector 1')
xlabel('Time (s)')
ylabel('Amplitude')
ylim([-1 1.1])
xlim([0 N/FS])
hold on;
plot(maxtab(:,1)/FS, maxtab(:,2), 'ro')
plot(mintab(:,1)/FS, mintab(:,2), 'ko')
max_col = maxtab(:,1);
peaks_det = max_col/FS;
No_of_peaks = length(peaks_det);
[song,FS] = wavread('C major.wav');
%---------------------------Performing STFT--------------------------------%
h = 1;
for i = 2:No_of_peaks
song_seg = song(max_col(i-1):max_col(i)-1);
L = length(song_seg);
NFFT = 2^nextpow2(L); % Next power of 2 from length of y
seg_fft = fft(song_seg,NFFT);%/L;
U = size(seg_fft,1)
% In harmonic prodcut spectrum, you downsample the fft data several times and multiply all those with the original fft data to get the maximum peak.
%HPS
seg_fft = seg_fft(1 : size(seg_fft,1)/2 );
seg_fft = abs(seg_fft);
%HPS: downsampling
for i = 1:length(seg_fft)
seg_fft2(i,1) = 1;
seg_fft3(i,1) = 1;
seg_fft4(i,1) = 1;
% seg_fft5(i,1) = 1;
end
for i = 1:floor((length(seg_fft)-1)/2)
seg_fft2(i,1) = (seg_fft(2*i,1) + seg_fft((2*i)+1,1))/2;
end
for i = 1:floor((length(seg_fft)-2)/3)
seg_fft3(i,1) = (seg_fft(3*i,1) + seg_fft((3*i)+1,1) + seg_fft((3*i)+2,1))/3;
end
for i = 1:floor((length(seg_fft)-3)/4)
seg_fft4(i,1) = (seg_fft(4*i,1) + seg_fft((4*i)+1,1) + seg_fft((4*i)+2,1) + seg_fft((4*i)+3,1))/4;
end
%HPS, PartII: calculate product
p1 = (seg_fft3) .* (seg_fft4);
p2 = p1.* (seg_fft2);
p3 = p2.* (seg_fft);
HPS, PartIII: find max
[f_y1,I] = max(p3)
for c = 1 : length(p3)
if(p3(c,1) == f_y1)
index = c;
end
end
% Convert that to a frequency
f_y(h) = (index / NFFT) * FS;
h=h+1;
f_y = abs(f_y)';
end
Before implementing p3 = p2.* (seg_fft); the sizes of seg_fft, seg_fft2, seg_fft3, seg_fft4 all have the same dimensions of 16384 1. Then when I DO implement p3 = p2.* (seg_fft); the size of seg_fft changes to 8192 1 while the sizes of rest remain at 16384 1 thus causing an error in multiplication as the dimensions aren't the same.
I'm really confused as to why this keeps happening and nothing I try seems to work out. Would really REALLY appreciate some help here... If someone could fix this code it'd be a GREAT help... Thanx in advance.. I'm real desperate here......