Simplified tone detector for PCM channel

A digital correlator for detecting multifrequency signaling tones is described. The theory is first presented for a continuous correlator using a fixed sine wave burst. A substitution, using a change in the time reference of the correlating sine wave, is then introduced. By introducing this change, a modified computational algorithm is derived which reduces the number of multiplications required at each sampling instant to four. For the digital implementation, the effects of sampling and quantization of the internal arithmetic are discussed.