Error Reduction Method for a Digital Signal Processing Voice and Audible Telephone Ring Tone Detection Algorithm
Original Publication Date: 1986-Feb-01
Included in the Prior Art Database: 2005-Mar-08
A method is described for reducing errors in algorithms which distinguish voice energy from energy due to other signals. One voice detection algorithm for which this process may be used is implemented in a system which seeks to detect when a called party answers a telephone call. In this case it is necessary to distinguish between a ringback signal and a voice signal. The ringback signal is composed of frequencies below the cutoff frequency of a low-pass filter. However, due to delay characteristics inherent in the type of low-pass filter chosen for the algorithm (fifth order elliptic), during the leading and falling edges of the ringback signal the DC level of the low-pass filter's output may fall below the DC level of the non-filtered input for a very short period of time.