Graphics Programs Reference

In-Depth Information

the periodograms of the blocks, and averages the periodograms at each

frequency. This is a technique commonly used to reduce the variance

of the PSD. For example, we can compare the variance of the above

estimate to that of a single periodogram by telling spectrum to use a

blocklength equal to the length of the signal:

spectrum(y,8192)

You can also specify windows to reduce spectral leakage, sampling fre-

quencies to get correct frequency scales and overlapping blocks. If you

are interested in PSD estimation, the Signal Processing toolbox contains

other methods of PSD estimation including Welch's method, MUSIC,

maximum entropy and multitaper. matlab also provides a graphical

user interface for spectral estimation as part of its interactive signal pro-

cessing environment
sptool
. The System Identification toolbox also con-

tains algorithms for PSD estimation (type
iddemo
and choose option 5

for a demonstration).

19

Sounds in MATLAB

matlab can send data to your computer's speaker, allowing you to visu-

ally manipulate your data, and listen to it at the same time. A digitised

recording of an interesting sound is contained in the mat-file
chirp.mat
.

Load this data, do a plot, and listen to the sound by typing:

load chirp

plot(y)

sound(y)

The volume of the sound can be controlled from within matlab using

the
soundsc
function and supplying an upper and lower limit. Or if

you wish, you can use your computer's system software to control the

volume. On UNIX the volume of the sound can be controlled with the