Digital Signal Processing Reference
In-Depth Information
Table 8.12
DTMF Frequencies and Their Frequency
Bins
k
[
f
Frequency Bin:
f
s
3
N
DTMF Frequency (Hz)
697
18
770
20
852
22
941
24
1209
31
1336
34
1477
38
0
Hz
18
()
A
18
logic
vn
18
()
0
Hz
20
()
A
20
logic
vn
20
()
1
Hz
22
()
A
22
logic
xn y n
()
()
vn
22
()
7
7
0
logic
Hz
24
()
A
24
logic
DTMF Tone
vn
24
()
1
Hz
31
()
logic
A
31
vn
31
()
0
A
34
logic
Hz
34
()
vn
34
()
0
Hz
38
()
logic
A
38
vn
38
()
Threshold
(
AAAAAAA
18
)
/
4
20
22
24
31
34
38
FIGURE 8.55
DTMF detector using the Goertzel algorithm.
EXAMPLE 8.29
Given a DSP system with f
s
¼ 8;000 Hz and data size N ¼ 205, seven Goertzel IIR filters are implemented for
DTMF tone detection. Determine the following for the frequencies corresponding to key 7.
a. Frequency bin numbers
b. The Goertzel filter transfer functions and DSP equations
c. Equations for calculating amplitude spectral values
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