Introduction to Digital Signal Processing - Digital Signal Processing: Fundamentals and Applications - page 6

2 x 10 4

Speech data: "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

Sample number

200

150

100

50

0

0 500 1000 1500 2000 2500 3000 3500 4000

Frequency (Hz)

FIGURE 1.6

Speech samples and speech spectrum.

Gain

Tweeter:
The crossover passes
high frequencies

Digital
highpass filter

Digital
audio x ( n

Gain

Woofer:
The crossover passes
low frequencies

Digital
lowpass filter

FIGURE 1.7

Two-band digital crossover.

displacement currents in leads or in the body of the patient, effects from equipment interconnections,
and other imperfections. Although using proper grounding or twisted pairs minimizes such 60-Hz
effects, another effective choice can be use of a digital notch filter, which eliminates the 60-Hz
interference while keeping all the other useful information. Figure 1.8 illustrates a 60-Hz interference
eliminator using a digital notch filter. With such enhanced ECG recording, doctors in clinics could give
accurate diagnoses for patients.