Finite Impulse Response Filter Design - Digital Signal Processing: Fundamentals and Applications - page 257

1 x 10 4

0.5

0

-0.5

-1

0 0.05 0.1 0.15 0.2 0.25

Number of samples

800

600

400

200

0

0 500 1000 1500 2000 2500 3000 3500 4000

Frequency (Hz)

FIGURE 7.24B
Enhanced speech and its spectrum.

Figure 7.24A shows the plots of the recorded noisy speech and its spectrum. As we can see in the
noisy spectrum, the noise level is high and broadband. After applying the designed lowpass filter, we
plot the filtered speech and its spectrum shown in Figure 7.24B , where the clean speech is clearly
identified, while the spectrum shows that the noise components above 2 kHz have been completely
removed.

7.4.3 Noise Reduction in Vibration Signals
In a data acquisition system for vibration analysis, we captured a vibration signal using an acceler-
ometer sensor in the noisy environment. The sampling rate is 1,000 Hz. The captured signal is
significantly corrupted by a broadband noise. Vibration analysis requires the first dominant frequency
component in the range 35 to 50 Hz to be retrieved. We list the filter specifications below:

Filter type ¼ bandpass FIR filter
Passband frequency range ¼ 35-50 Hz
Passband ripple ¼ 0.02 dB
Stopband frequency ranges ¼ 0-15 and 70-500 Hz
Stopband attenuation: 50 dB