Fundamental accuracy limitations for pilot-tone time-base correction

Wiener filtering concepts are applied to the problem of determining the accuracy limitations for a pilot-tone time-base correction system. Pilot-tone time-base correction is currently employed in speed control of tape recorder drives, vernier data correction by means of voltage-controlled delay lines in wideband tape recorders, as well as synchronized sound-on-film devices. In this system, the correction is accomplished by the addition of a stable sinusoid in a clear area of the signal baseband. After transmission through a medium with varying time delay and additive noise, the pilot tone is recovered by a tracking filter. The output of the tracking filter can be used to estimate the variations in time delay of the transmission medium. A statistical optimization is then performed to find the minimum residual time-base error in the desired signal after correction by such a system. The theory of parameter estimation indicates that the system described is near optimum and represents a lower bound on achievable accuracy. The results for the special case of white bandlimited time-delay variations are presented in the form of curves.