Classical tone detectors use narrow bandpass filters to isolate tones. A comparison of a filter's output power against the total input signal power determines whether or not a particular tone is present. This paper considers an alternate method for tone detection. It is based on estimating the first three moments of the signal's band-limited power spectrum. These three moments (zeroth, first, and second) measure the power, power mean frequency, and RMS power bandwidth, respectively, of the signal. If these three moments are available, it is easy to deduce whether or not a tone is present. Since the estimators have a simple digital implementation, this approach should have economic advantages in many applications.
Available at: http://works.bepress.com/jeffrey_denenberg/6/