Peak interpolation in frequency domain

Hi Everyone,

I am trying to do some peak interpolation in the freq domain.. I am zero padding already in the time domain however trying to get the peaks centered more around the correct bin. Any suggestions on how to do this with my current code?

Thanks!

Mike

Fs =5000;            % Sampling frequency                    
x=data;       %Truncated to increase bin width for testing
T = 1/Fs;             % Sampling period       
L = length(x);             % Length of signal
t = (0:L-1)*T;        % Time vector
x = x-mean(x);        %subtract DC signal component



%DFT without window or Interpolation
xdft = fft(x);

xdft = xdft(1:length(x)/2+1);
xdft = xdft/length(x);
xdft(2:end-1) = 2*xdft(2:end-1);
freq = 0:Fs/length(x):Fs/2;


%Add Hanning Window without zero padding

nfft = 2^nextpow2(L); % Transform length
y_HannWnd = x.*hanning(L); 
Ydft_HannWnd = fft(y_HannWnd,nfft);%/L;
Ydft_HannWnd = Ydft_HannWnd(1:L/2+1);
Ydft_HannWnd(2:end-1) = 2*Ydft_HannWnd(2:end-1);
P2H = abs(Ydft_HannWnd/L);
P1H = P2H(1:L/2+1);
P1H(2:end-1) = 2*P1H(2:end-1);
f = Fs*(0:(L/2))/L;


% %Hanning window with zero padding
% 
% lpad = 2*length(x);
% 
% xpad = padarray(x,lpad);
% 
% Lp = length(xpad);
% 
% 
% nfftpad = 2^nextpow2(Lp); % Transform length
% 
% 
% y_HannWndpad = x.*hanning(L);
% 
% 
% Ydft_HannWndpad = fft(y_HannWndpad,nfftpad)/Lp;
% 
% 
% 
% Ydft_HannWndpad = Ydft_HannWndpad(1:(Lp)/2+1);
% Ydft_HannWndpad(2:end-1) = 2*Ydft_HannWndpad(2:end-1);
% 
% P2Hpad = abs(Ydft_HannWndpad/Lp);
% P1Hpad = P2Hpad(1:(Lp)/2+1);
% P1Hpad(2:end-1) = 2*P1Hpad(2:end-1);
% fpad = Fs*(0:(Lp/2))/Lp;

%Hanning window with zero padding

lpad = 10*length(x);
xpad = padarray(x,lpad);
Lp = length(xpad);
nfftpad = 2^nextpow2(Lp); % Transform length
y_HannWndpad = x.*hanning(L);
Ydft_HannWndpad = fft(y_HannWndpad,lpad);
Ydft_HannWndpad = Ydft_HannWndpad(1:(lpad)/2+1);
Ydft_HannWndpad(2:end-1) = 2*Ydft_HannWndpad(2:end-1);
P2Hpad = abs(Ydft_HannWndpad/lpad);
P1Hpad = P2Hpad(1:(lpad)/2+1);
P1Hpad(2:end-1) = 2*P1Hpad(2:end-1);
fpad = Fs*(0:(lpad/2))/lpad;

%% Zero Padding for Interpolation no Hanning window
lpad = 4*length(x);
xdftpad = fft(x,lpad);
xdftpad = xdftpad(1:lpad/2+1);
xdftpad = xdftpad/length(x);
xdftpad(2:end-1) = 2*xdftpad(2:end-1);
freqpad = 0:Fs/lpad:Fs/2;


%Plot time-domain signal
subplot(6,1,1);
plot(t, x);
ylabel('Amplitude'); xlabel('Time (secs)');
axis tight;
title('Shaker Input Signal');

subplot(6,1,2);
%plot(freq,abs(xdft));
title('DFT no padding or Hann')
xlabel('t (milliseconds)')
ylabel('X(t)')

%Hold on 
subplot(6,1,3);
plot(freqpad,abs(xdftpad),'c')
 
title('Single-Sided Amplitude Spectrum of X(t)')
xlabel('f (Hz)')
ylabel('|P1(f)|')
%ylim([0,2000]);


subplot(6,1,4);
plot(f,P1H,'r') 
title('Hann FFT')
xlabel('f (Hz)')
ylabel('|P1(f)|')
%ylim([0,2000]);


subplot(6,1,5);

plot(fpad,P1Hpad,'g') 
title('Hann plus zero padding dFT')
xlabel('f (Hz)')
ylabel('|P1(f)|')
%ylim([0,2000]);


subplot(6,1,6);

plot(freq,abs(Ydft_HannWnd),'r') 
title('Hann FFT')
xlabel('f (Hz)')
ylabel('|P1(f)|')
%ylim([0,2000]);