an apparatus for determining the presence of a tone in an input signal includes memory circuitry and data processing circuitry coupled to the memory circuitry . the data processing circuitry is operative to receive multiple samples of the input signal , and to determine a first value at least in part by multiplying each of the samples by respective ones of a first set of values for an impulse response and summing the results . the data processing system is also operative to determine a second value at least in part by multiplying each of a portion of the samples by respective ones of a second set of values for the impulse response and summing the results . the data processing system is operative to determine the power of the tone in the multiple samples of the input signal at least in part by utilizing the first value and the second value .