Spectral Moment Estimators: A New Approach to Tone Detection

The use of tones is proliferating with the growth of the directdistance-dialing (DDD) network. Tones are used for multifrequency signaling, Touch-Tone® signaling, etc.; for milliwatt tone testing, testing in carrier transmission maintenance, 1 etc.; and as audible ring indicators, reorder indicators, etc. The DDD network is now evolving toward an integrated system of digital transmission and digital switching. Continued use of analog tone detectors in this digital environment is impractical because of the expense of interfacing analog and digital systems. Classical tone detectors do not lend themselves to efficient digital implementation. Therefore, new approaches to tone detection are necessary. 143 Several methods are currently under investigation including classical digital filters,2 the discrete Fourier transform, 3 ' 4 and the use of counting techniques. 5 This paper details another approach to tone detection which is amenable to digital implementation: spectral moment estimation. II. TONE DETECTION 2.1 Classical tone detectors