Finite Impulse Response Filter Design - Digital Signal Processing: Fundamentals and Applications - page 258

According to these specifications, we can determine the following parameters for the filter design:

Window type ¼ Hamming window
Number of filter taps ¼ 167
Low cutoff frequency ¼ 25 Hz
High cutoff frequency ¼ 65 Hz

Figure 7.25 displays the plots of the recorded noisy vibration signal and its spectrum. Figure 7.26
shows the retrieved vibration signal with noise reduction by a bandpass filter.

7.4.4 Two-Band Digital Crossover
In audio systems, there is often a situation where the application requires the entire audible range of
frequencies, but this is beyond the capability of any single speaker driver. So, we combine several
drivers, such as the speaker cone and horns, each covering a different frequency range, to reproduce the
full audio frequency range.
A typical two-band digital crossover can be designed as shown in Figure 7.27 . There are two
speaker drivers. The woofer responds to low frequencies, and the tweeter responds to high frequencies.
The incoming digital audio signal is split into two bands by using a lowpass filter and a highpass filter
in parallel. We then amplify the separated audio signals and send them to their respective corre-
sponding speaker drivers. Hence, the objective is to design the lowpass filter and the highpass filter so

1

0

-1

-2

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Number of samples

0.04

0.03

0.02

0.01

0

0 50 100 150 200 250 300 350 400 450 500

Frequency (Hz)

FIGURE 7.25
Noisy vibration signal and its spectrum.