Tone-detection method for detecting at least one tone in a dual-tone multifrequency signal, call-progress method using the same

A method for determining a presence of single tone multifrequency and dual tone multifrequency signals in signals provided over a telephone network including the following steps:

• receiving the signals from the telephone network;
• determining a maximum value A max of the received signal during a sampling window and a measure E of the energy;
• computing a ratio, ##EQU18## comparing the said ratio r to a first threshold value and indicating receipt of a single tone signal when a value of the ratio r is less than the said first threshold value;
• when reception of a single tone signal is indicated subjecting the received signal to a second order autoregressive process to obtain at least one estimate of autoregressive parameters of the received signal and at least one digital band-pass filtering operation adjusted by results of an estimate to remove noise components from the received signal and computing a frequency of the tone signal from a value of the estimated parameters;
• comparing the said ratio r to a higher second threshold value when the ratio r exceed said first threshold value and indicating receipt of a dual tone signal when the ratio r is less than said second threshold value;
• and,
• when reception of a dual tone signal is indicated subjecting the received signal to a fourth order autoregressive process to obtain at least one estimate of the autoregressive parameters of the received signal and at least one digital band-pass filtering operation adjusted by the results of the estimate to remove noise components from the received signal and computing the frequencies of the received dual tones from the value of the estimated parameters.