AMBE-2000 Digital Voice Systems, Inc., AMBE-2000 Datasheet - Page 33

• Manufacturer Part Number: AMBE-2000
• Description: 2.0 - 9.6 KBPS Single ic For Toll-quality, Low Data Rate, Real Time Speech Compression
• Manufacturer: Digital Voice Systems, Inc.

5.3.8
This word corresponds to the DTMF Detection capabilities of the vocoder. It uniquely identifies specific tones recognized by
the encoder. See table 5-M for a list of tones and their corresponding values.
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DTMF Tone Detection
Frequency Tolerance
Maximum Frequency
Signal to Noise
Distortion ratio
Reverse Twist
Tone Duration
Normal Twist
Requirement
MSB
Input Level
Framed Output: Word 10 : DTMF Control
Tolerance
15:
Minimum
Minimum
Minimum
Minimum
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Range
Range
14
13
Table 5-K DTMF Tone Detection Parameters
Table 5-L DTMF Control Format
DTMF Amplitude
-25 dBm0
8-10 dB
4-10 dB
±1.5%
±3.5%
45 ms
Value
15 dB
12
11
Description
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).
In order for an input signal to correspond to a valid DTMF tone, the ratio of in-band to out-of-
band energy must be greater than 15dB. In-band 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 in-band
energy.
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.
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.
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.
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.
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.
DTMF Control – 8-bits (See Table 1-F)
10
AMBE-2000™ Vocoder Chip
User’s Manual Version 4.0
9
8
7
6
DTMF Digit Detect/ Generate
5
4
3
2
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