SIGNAL PROCESSING - Biomechanics and Motor Control of Human Movement - page 24

500

400

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100

0

− 100

− 200

− 300

− 400

− 500

0 0.1 0.2

Time (sec)

0.3 0.4 0.5

( a )

1

0.8

0.6

0.4

0.2

0

− 100 − 80 − 60 − 40 − 20 0 20 40 60 80 100

− 0.2

− 0.4

τ (msec)

( b )

Figure 2.6 (a) is a surface EMG signal recorded for 0.5 sec that does not show the
presence of any 60 Hz hum pickup. (b) is the autocorrelation of this EMG over a
τ =± 100 ms. Again, note that this is an even function and observe the presence of

a periodic component closely resembling a sinusoidal wave with peaks equal to the
period of a 60 Hz (approximately 17 ms).