E1C02 09/14/2010
13:35:22 Page 73
This signal should be represented as a discrete time signal by computing the value of the function at
equally spaced time intervals. An appropriate time interval for this signal would be 0.05 s. Examine
the signal with averaging windows of 4 and 30 points.
2.6 The data file in the companion software noisy.txt provides discrete time-varying signal that contains
random noise. Apply a 2-, 3-, and 4-point moving average (see Problem 2.5) to these data, and plot
the results. How does the moving average affect the noise in the data? Why?
2.7 Determine the value of the spring constant that would result in a spring-mass system that would
execute one complete cycle of oscillation every 2.7 s, for a mass of 0.5 kg. What natural frequency
does this system exhibit in radians/second?
Moving average window
–2
–1
0
1
2
y(t)
2
0
4
14
12
10
8
6
Time
Figure 2.22 Moving average and windowing.
y(t)
1
0.8
0.6
0.4
0.2
0
–0.2
–0.4
–0.6
–0.8
–1
–1.2
14
12
10
8
6
4
2
Time
Figure 2.23 Effect of moving average on signal illustrated in Figure 2.22.
Problems 73