Patent ID: 7161962

Claim:
A method of determining whether a voice signal communicated over a digital voice network includes a modulated data signal, the method comprising the steps of: a) determining whether an answer tone is present in the voice signal; b) when an answer tone is present, performing the steps of: i) locating a first phase reversal in the voice signal, including: 1) performing an autocorrelation of a segment of the voice signal; 2) searching for the lowest value of the autocorrelation of the segment of the voice signal; 3) comparing the determined lowest value of the autocorrelation to a predetermined value; and 4) indicating a phase reversal has occurred when the determined lowest value is less than the predetermined value; ii) locating a second phase reversal in the voice signal, the second phase signal being the next consecutive phase reversal in the voice signal after the first phase reversal; iii) determining the time interval between the location of the first phase reversal in the signal and the second phase reversal in the voice signal; and iv) indicating that the voice signal includes a modulated data signal when the determined time interval is between a predetermined range of time values.