PRACTICAL MATLAB® FOR ENGINEERS PRACTICAL MATLAB

Time Domain Representation of Continuous and Discrete Signals 55

MATLAB Solution

% Script file: audio

subplot(2,1,1)

fo = 1000;

Fs = 8000;Ts =1/Fs;

t = 0:Ts:1;

y = cos(2*pi*fo.*t)+3*cos(0.5*pi*fo.*t); % audio sequence

plot(t(1:100),y(1:100));

ylabel(‘Amplitude’);

xlabel(‘time (sec)’);

title(‘cos(2\pi fo t)+3 cos(0.5\pi fo t) vs.t ‘)

subplot(2,1,2)

load mtlb; Fs=1418; T=1/Fs;

x = 1:4001;xx=x.*T; % speech file

plot(xx,mtlb);

axis([0 4000*T -4 4]);

ylabel(‘Amplitude ‘);

title(‘[Speech file mtlb] vs. t’);

xlabel(‘time (sec)’)

R.1.167 The MATLAB command [y, Fs, nbits] = wavread(‘microsoft_fi le’) returns the vector y

consisting of the audio wave samples from a Microsoft fi le, at a sampling frequency

Fs, using n bits to encode each sample of y, whereas the amplitude of y is scaled

over the range − 1 ≤ y ≤ + 1. Similarly, the command wavwrite returns a Microsoft

wave fi le.

R.1.168 The MATLAB command image(matrix_ A) returns matrix_A as an image, where

each element of the matrix_A is defi ned by a color. The matrix dimensions may

be 2-D (m × n) or 3-D (m × n × r). In its simplest version, the elements of the 2-D

(n × m) matrix are used as indices in the current colormap to defi ne its color.

FIGURE 1.45

Plots of audio and speech fi les of R.1.166.

cos (2π fo t) + 3 cos (0.5π fo t) versus t

4

2

0

− 2

− 4

0 0.002 0.004 0.006 0.008 0.01 0.012 0.014

time (sec)

time (sec)

[Speech file mtlb] versus t

4

2

0

− 2

− 4

0 0.5 1 1.5 2 2.5

Amplitude

Amplitude