Digital Signal Processing Reference
In-Depth Information
2 2
f
L
s
z
z
1
1
sin
cos
Hz
()
L
L
2
12
z
L
DTMF Tones
A
()
yn
7
7
1
z
z
sin
cos
Hz
H
H
12
1
z
2
H
2
1209
f
H
s
FIGURE 8.51
Digital DTMF tone generator for the keypad digit “7”.
Here we generate the DTMF tone for key “7” for a duration of one second, assuming a sampling
rate of 8,000 Hz. The generated tone and its spectrum are plotted in
Figure 8.52
for verification, while
the MATLAB implementation is given in Program 8.19.
2
1
0
-1
-2
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
0.045
0.05
Time (second)
1
0.8
0.6
0.4
0.2
0
0
500
1000
1500
2000
2500
3000
3500
4000
Frequency (Hz)
FIGURE 8.52
Plots of the generate DTMF tone of “7” and its spectrum.
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