Design and Implementation of a Time-Domain PDA for Undistorted and Band-Limited Signals

This chapter describes the design and implementation of a time-domain PDA for undistorted and band-limited signals. The PDA applies a simplified inverse filter in the preprocessor and a threshold analyzer with hysteresis in the basic extractor. This configuration (Hess, 1972b, 1976a, b), which is discussed in Sect.7.1, corresponds to principle PiTL (see Sects.6.1,4). The performance evaluation, however, has shown that this PDA fails systematically with band-limited signals and, in addition, that the PDA tends to fail occasionally when the formant F1 coincides with F0. Reconstruction of the first partial by nonlinear distortion is one possible way out of this problem. Since the opinion in the literature is not uniform as to what kind of nonlinear distortion is suitable to optimally enhance the first partial, this question has been expermentally investigated (Sects.7.2, 3). Experiments show that no single nonlinear function is optimal for any signal. A combination of three functions (odd, even, and rectified single-sideband modulation), however, gives good results in most of the cases (Sect.7.4). This result leads to the implementation of the three-channel PDA discussed in Section 7.5. The three channels result from the application of the three nonlinear functions mentioned above. The nonlinear distortion represents the first step of the PDA, and the subsequent steps of the preprocessor and the basic extractor, which are performed for each channel separately, correspond to the linear implementation.