NSAM266SAASLASHV datasheet(26/52 Pages) NSC

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20 Software (Continued)

TABLE 2-1 DTMF Detector Performance

PLAY

RECORDIDLE

Detection Sensitivity (Note A)

Performance Depends on Message

40 dBm

Being Played (Note B)

Accepted DTMF Length

50 ms

40 ms

Frequency Tolerance

15%

SN Ratio

12 dB

Minimum Spacing (Note C)

50 ms

45 ms

Normal Twist

8 dB

Reverse Twist (Note D)

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

34 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 214

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

TLEE12584 – 27

FIGURE 2-1 Busy and Dial-Tone Band-Pass Filter Frequency Response

TLEE12584 – 28

E1 b E3 k 90 ms

S1 b S3 k 90 ms

90 k Ei k 1650 ms

65 k Si k 1250 ms

FIGURE 2-2 Busy-Tone DetectorCadence Specification

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