Digital Voice Systems AMBE-2020, Руководство пользователя

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AMBE-2000™ Vocoder Chip Users Manual
Version 4.92, June, 08
DVSI Confidential Proprietary, Subject to Change Page 36
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Table 5-K DTMF Tone Detection Parameters
DTMF Tone Detection
Requirement
Value Description
Minimum
Input Level
-25 dBm0
An input signal shall not be rejected as a DTMF tone if its amplitude is greater than -25 dBm0
(maximum sinusoid dBm0 is defined as+3.17 dBm0).
Minimum
Signal to Noise
Distortion ratio
15 dB
In order for an input signal to correspond to a valid DTMF tone, the ratio of inband to out-of-
band energy must be greater than 15dB. Inband energy is defined to be the energy in
frequency components within
±
3.5% of the two frequencies defined by the DTMF
frequencies. Out-of-band energy is defined to be the total energy minus in the inband
energy.
Minimum
Frequency Tolerance
±
1.5%
An input signal shall not be rejected as a DTMF tone if both of its principal frequency
components are within
±
1.5% of the frequencies needed for the DTMF tone.
Maximum Frequency
Tolerance
±
3.5%
An input signal shall be rejected as a DTMF tone if either of its principal frequency
components are outside
±
3.5% of the frequencies needed for the DTMF tone.
Normal Twist
Range
8-10 dB
An input signal does not correspond to a valid DTMF tone if the energy contained within the
low frequency band is more than 10 dB greater than the energy contained in the high
frequency band. An input signal shall not be rejected as a DTMF if energy contained within
the low frequency band is less than 8 dB greater than the energy contained in the high
frequency band. Each low and high frequency band is limited to
±
3.5% of the frequencies
needed for the DTMF tone.
Reverse Twist
Range
4-10 dB
An input signal does not correspond to a valid DTMF tone if the energy contained within the
high frequency band is more than 10 dB greater than the energy contained in the low
frequency band. An input signal shall not be rejected as a DTMF if energy contained within
the high frequency band is less than 4 dB greater than the energy contained in the low
frequency band. Each low and high frequency band is limited to
±
3.5% of the frequencies
needed for the DTMF tone.
Minimum
Tone Duration
45 mS
An input signal shall not be rejected as a DTMF tone as long as its time duration is greater
than 45 mS. In addition a minimum of two frames will be transmitted of the DTMF tone if a
valid tone is detected. The duration of a tone is defined by the points at which the envelope
is 20 dB below its peak value.
Table 5-L DTMF Control Format
DTMF Control – 8-bits (See Table 1-F)
15:
MSB
14 13 12 11 10 9 8 7 6 5 4 3 2 1
0:
LSB
DTMF Amplitude DTMF Digit Detect/ Generate