| 摘要 |
Disclosed herein is a three-way call detection system and method for detecting the addition of a third party to a pre-existing telephonic connection between a first party and a second party. The system comprises: a meter for measuring the amplitude of a line voltage of a telephonic connection between a first party and a second party, said line voltage having a frequency band F 1 ; a first filter to remove a frequency band F 2 from said line voltage and output a filtered signal, said frequency band F 2 being a subset of F 1 ; a white noise generator for generating a low level white noise signal with a frequency band that corresponds to F 2 and with an amplitude that is significantly below an amplitude level of the measured line voltage for frequency band F 2 ; a coupler for combining the low level white noise signal to the filtered signal, thereby outputting an additive line voltage; a second filter that passes only a portion of the additive line voltage, said signal that passes being referred to as the band-passed signal, said band-passed signal having a frequency range F 3 , said frequency band F 3 being a subset of F 1 and being inclusive of F 2 ; and a processor for processing the band-passed signal and determining a baseline amplitude level associated with a two-way call. The processor monitors the band-passed signal in the time domain for a shift in baseline amplitude level, which shift is associated with the addition of a third party to the telephonic connection. The white noise being added is preferably at least 3 dB below the amplitude level of the measured line voltage, more preferably at least 10 dB, more preferably at least 20 db, and most preferably 40 db below. The frequency band F 2 is selected from F 1 to be significantly large enough to permit more reliable detection, and yet small enough to be barely perceptible to the listener. For example, F 2 may comprise the frequencies from 1-2 KHz. An F 2 of 1-1.3 KHz. also functions well.
|
