| 摘要 |
Tone-detection method for a call-progress process which detects at least one tone in a multifrequency dual-tone signal in a telecommunication apparatus having digital signal processing resources. The method involves the step of: - computing (201) the value of the energy of the signal, - processing (201) said received signal to determine the existence of one or twotones in said signal, - applying a second-order or fourth-order autoregressive process in response to said determination and performing (203, 208) a first estimation of the autoregressive parameters of said received signal, - performing a digital band-pass filtering operation (205,210) adjusted to the result of the estimation of said autoregressive parameters to provide a partial elimination of the noise existing on said received signal, - reapplying (205, 210) a second-order or fourth-order autoregressive process in response to said determination and performing a final estimation of the autoregressive parameters of said received signal, - computing (206, 211) the values of the frequencies each tone from the value of said estimated parameters. The determination of the number of tones existing in the signal is achieved by the computation of the ratio: <IMG> which is theorically equal to 2 in the case of a unique tone, and conversely should be 4 in that of a dual tone. The first and final second-order autoregressive process are based on the predicting function having the ztransfer function: <IMG> and which is associated with a Least Mean Square algorithm continuously adapting the parameters of the predictor in a sense allowing the minimizing of an error signal. On the other hand, the first and final fourth-order autoregressive process are based on the predicting function having the ztransfer function: <IMG> To increase the accuracy of the tone-detection mechanism, the second-order autoregressive function is performed with the value of a2 parameter being constantly fixed to -1. Similarly, the fourth-order autoregressive process is performed with the values of a3 and a4 being respectively equal to a? and -1. The digital filter which provides the suppression of most of the noise existing in the signal having an unique tone is based on the z-transfer function: <IMG> In the case of a dual-tone, the filtering is based on the function: <IMG> Fig. 2
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