Formant Estimation- HOW TO FIND FORMANTS

How to find formants having wav file. I must get that effect http://www.mathworks.com/matlabcentral/fx_files/8959/1/screen_shot.jpg but i dont now how.

what i have is only this :

[x,fs]=wavread('ola.wav');
x=resample(x,10000,fs);
% plot waveform
t=(0:length(x)-1)/fs;       % dlugosc probkowanych ramek
figure;
subplot(2,1,1)
plot(t,x);
legend('Waveform');
xlabel('Time (s)');
ylabel('Amplitude');
n=length(x)

% get Linear prediction filter

ncoeff=2+fs/1000; % rule of thumb for formant estimation

a=lpc(x,ncoeff); % plot frequency response [h,f]=freqz(1,a,length(x)); subplot(2,1,2); % convert h to dB dBh=20*log10(abs(h)+eps); plot(dBh); legend('LP Filter'); xlabel('Liczba probek'); ylabel('Gain (dB)');