%% Bandwidth Expansion of LPC Speech Spectrum
% Load a speech signal sampled at F_s=7418\;\rm Hz. The file contains a recording of a female voice saying the word "MATLAB®."

load mtlb

%
% Model a 100-sample section of the signal using a 12th-order autoregressive polynomial. Perform bandwidth expansion of the signal by scaling the roots of the autoregressive polynomial by 0.85.

Ao = lpc(mtlb(1000:1100),12);
Ax = polyscale(Ao,0.85);

%
% Plot the zeros, poles, and frequency responses of the models.

subplot(2,2,1)
zplane(1,Ao)
title('Original')

subplot(2,2,3)
zplane(1,Ax)
title('Flattened')

subplot(1,2,2)
[ho,w] = freqz(1,Ao);
[hx,w] = freqz(1,Ax);
plot(w/pi,abs([ho hx]))
legend('Original','Flattened')

% Copyright 2012 The MathWorks, Inc.