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MX663DW

Call Progress Decoder

MX-COM Inc  

Call Progress Decoder

6

MX663 Preliminary Information

4. General Description

4.1 Overall Function Description

The MX663 consists of a Call Progress Tone Detector, a 620Hz Detector and a Level Detector.

The MX663 Call Progress Tone Detector uses different tone detection methods from those commonly found

with other products.

Many traditional devices use a bandpass filter followed by an energy detector. The filter is usually designed

to pass input signals with a frequency between about 300Hz and 700Hz, and the amplitudes of signals in this

range are then checked against a level threshold. Any signal of acceptable level in this frequency band is

classed as a Call Progress tone, including signals due to speech and noise. False outputs caused by speech

are a common feature with these products, and background noise may lead to a stuck "detect" output.

The MX663, by contrast, uses a stochastic signal processing technique based on analysis in both the

frequency and time domain, with signal amplitude forming a small part in the decision process. This analysis

includes checks on whether the signal has a "profile" which matches international standards for Call Progress

tones, or a profile more likely to match that of speech, noise or other non-call-progress signals. It also adds

checks on whether tones which include frequencies corresponding with the "US Busy" signals, Special

Information Tones and Fax/Modem Tones have been detected.

4.2 Glossary

Call Progress Tones: The single and dual frequency tones in the range 350Hz to 620Hz specified widely for

call progress signaling.

Call Progress Band: The nominal range 340Hz to 700Hz within which the MX663 will detect Call Progress

tones. The detection algorithm requires that the tones have the characteristics typical of Call Progress Tones.

620Hz Detection: The nominal range 590Hz to 650Hz. Single tones in this range, or dual tones having a

material frequency component within this range (e.g. 480 + 620Hz) will be detected.

Non Call Progress Signal: A signal falling within the nominal range (a) 190Hz to 895Hz, but NOT within the

Call Progress Band, or (b) within the nominal range 190Hz to 895Hz, but NOT meeting the DETECTION

REQUIREMENTS when the signal falls in the Call Progress Band.

Subject to the duration and other characteristics of such signals, the MX663 will usually interpret these as a

Non Call Progress Signal (e.g. speech or other signal activity).

Special Information Tone: The nominal frequencies 950Hz or 1400Hz or 1800Hz.

Fax/Modem Low Tone: The nominal frequency 1250Hz.

Fax/Modem High Tone: The nominal frequency 2150Hz.

Minimum Input Signal: The minimum signal level for the specified tone decoding performance. The lower

level at which absence of an input signal will be registered is not specified. However, a separate signal level

detector makes amplitude information available.

No Signal: A signal falling outside the nominal range 180Hz to 2280Hz or the absence of an input signal.

Either will be detected as a No Signal condition.

Nominal: Subject to dynamic tolerances within the signal analysis process. Absolute values are not material

or adverse to performance.

4.3 Block Diagram Description (Reference Figure 1)

4.3.1 SIGIN

The input signal is amplified by a self-biased inverting amplifier. The dc bias of this input is internally set at.

Accordingly, the input signal should be capacitively coupled to SIGIN.

© 1999 MX-COM Inc.

www.mxcom.com Tele: 800 638-5577 336 744-5050 Fax: 336 744-5054

Doc. # 20480165.003

4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA

All trademarks and service marks are held by their respective companies.

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