ANALYTIC SIGNAL GENERATION - TIPS AND TRAPS

In this correspondence we discuss methods to produce the discrete anal ytic signal from a discrete real-valued signal. Such an analytic signa l is complex and contains only positive frequencies. Its projection on to the real axis is the same as the original signal. Our use stems fro m instantaneous-frequency estimation and time-frequency signal analysi s problems. For these problems the negative frequency component of rea l signals causes unwanted interference. The task of designing a filter to produce an approximation to the ideal analytic signal is not as si mple as its formulation might suggest. Our result is that the direct m ethods of zeroing the negative frequencies, or using Hilbert transform fitters, have undesirable defects. We present an alternative which is similar to the ''quadrature'' filters used in modem designs.