Signal transmission using electronic signal processing. Transducers convert signals from other physical waveforms to electric current or voltage waveforms, which then are processed, transmitted as electromagnetic waves, received and converted by another transducer to final form. A number of well-known and frequently applied signal analysis and processing methods do not appear to be documented in the signal theory literature. While they are useful and widely used, these methods often do not involve the levels of innovation or theoretical descriptions that normally justify publication in signal processing journals, and their applications may be too narrow for inclusion in textbooks. Several lesser-known of these methods are described: (1) two-stage tuning; (2) cyclic frequency shifting; (3) frequency smoothing using the Lank-Reed-Pollon algorithm; (4) detecting "persistence;" (5) raising an analytic signal to non-integral powers; (6) adaptive notch filtering; and (7) noise-level estimation.
