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Nonlinear distortion is an adequate means to enhance the first harmonic of band-limited speech signals for pitch determination. A single nonlinear function, however, is not equally well suited for all kind of input signals. This paper first presents the results of an evaluation of 16 nonlinear functions as to their usefulness in preprocessors of pitch extractors. The results suggest the simultaneous application of three nonlinear functions: odd, even, and rectified SSB. Using these functions, a three-channel time-domain pitch extractor is implemented which, in its linear part, is a further development of a previous single channel pitch extractor applying a crude approximation of the inverse filter.