MX643

The MX643 Call Progress Tone Detector uses different tone detection methods from those commonly found with other Call Progress Tone Detectors.

 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. Each signal amplitude in this range is then checked against a level threshold. Any signal of acceptable level in this frequency band is classed as a Call Progress tone, including speech and noise. False outputs caused by speech are commonly indicated by such
products and background noise may lead to a stuck detect output.

In contrast, the MX643 uses a stochastic signal processing technique. This technique is based on analysis of both
the frequency and time domains, with signal amplitude forming a minor part in the decision process. This analysis
includes, checks on whether the signal has a profile which matches international standards for Call Progress
Tones, Special Information Tones, or a profile more likely to match that of speech, noise or other Non-Call
Progress signals. Checks are also performed to see if the signal is a single tone, and whether the tones which
include frequencies corresponding with the 'U.S. Busy' signals have been detected.