Digital Signal Processing Systems, Basic Filtering Types, and Digital Filter Realizations - Digital Signal Processing: Fundamentals and Applications - page 204

2 x 10 4

Speech: We lost the golden chain

1

0

-1

-2

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

x 10 4

Bandpass filtered speech

4000

2000

0

-2000

-4000

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

x 10 4

Number of samples

FIGURE 6.32B
Plots of the original speech and filtered speech.

As shown in Figure 6.32 C, the designed bandpass filter significantly reduces low-frequency
components, which are less than 1,000 Hz, and the high-frequency components above 1,400 Hz, while
letting the signals with the frequencies ranging from 1,000 Hz to 1,400 Hz pass through the filter.
Similarly, we can design and implement other types of filters, such as lowpass, highpass, bandpass, and
band reject (bandstop) to filter the signals and examine the performance of their designs. MATLAB
implementation details are given in Program 6.4.
Program 6.4. MATLAB program for bandpass filtering of speech.

fs ¼ 8000; % Sampling rate
freqz([0.0201 0.00 -0.0402 0 0.0201],[1 -2.1192 2.6952 -1.6924 0.6414],512,fs);
axis([0 fs/2 -40 1]); % Frequency response of bandpass filter

figure
load speech.dat
y ¼ filter([0.0201 0.00 -0.0402 0.0201],[1 -2.1192 2.6952 -1.6924 0.6414],speech);
subplot(2,1,1),plot(speech); grid; % Filtering speech

ylabel( ' Origibal Samples ' )
title( ' Speech: We lost the golden chain. ' )
subplot(2,1,2),plot(y);grid
xlabel( ' Number of Samples ' );ylabel( ' Filtered Samples ' )