NSAM266SA Datasheet, PDF (26/52 Pages) National Semiconductor (TI) – NSAM266SA CompactSPEECHTM Digital Speech Processor with Serial Flash Interface

2 0 Software (Continued)
TABLE 2-1 DTMF Detector Performance
PLAY
RECORD IDLE
Detection Sensitivity (Note A)
Performance Depends on Message
Being Played (Note B)
b40 dBm
Accepted DTMF Length
l _{50 ms}
l _{40 ms}
Frequency Tolerance
g1 5%
g1 5%
S N Ratio
12 dB
12 dB
Minimum Spacing (Note C)
l _{50 ms}
l _{45 ms}
Normal Twist
8 dB
8 dB
Reverse Twist (Note D)
4 dB or 8 dB
4 dB or 8 dB
Note A Performance depends on the DAA design
Note B Performance with echo canceler is 10 dB better than without echo canceler For a silent message Detection Sensivitiy is
b34 dBm with echo canceler
Note C If the interval between two consecutive DTMF tones is s 20 ms the two are detected as one long DTMF tone
If the interval between two consecutive DTMF tones is between 20 ms and 45 ms separate detection is unpredictable
Note D Determined by the DTMF REV TWIST tunable parameter value
OTHER DETECTORS
Detection of busy and dial tones and no-energy is con-
trolled by tunable parameters You should tune these pa-
rameters to fit your hardware For more information see the
TUNE command in Section 2 14
Dial and busy tone detectors work with a band-pass filter
that llmits the frequency range in which tones can be de-
tected to 0 Hz – 1100 Hz Its frequency response is illustrat-
ed in Figure 2-1 and the busy tone cadences in Figure 2-2
TONE GENERATION
The CompactSPEECH can generate DTMF tones and sin-
gle-frequency tones from 300 Hz to 3000 Hz in increments
of 100 Hz CompactSPEECH tone generation conforms to
the EIA-470-RS standard Note however that you may
have to change the value of some tunable parameters in
order to meet the standard specifications since the energy
level of generated tones depends on the analog circuits be-
ing used
 Tune the DTMF TWIST LEVEL parameter to control
the twist level of the generated DTMF tones
 Use the VC command and tune the TONE
GENERATION LEVEL parameter to control the energy
level at which these tones are generated
 Use the GT command to specify the DTMF tones and
the frequency at which single tones are generated
FIGURE 2-1 Busy and Dial-Tone Band-Pass Filter Frequency Response
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E₁ b E₃ k 90 ms S₁ b S₃ k 90 ms 90 k E_i k 1650 ms 65 k S_i k 1250 ms
FIGURE 2-2 Busy-Tone Detector Cadence Specification
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