A filterbank-based method of time-scale modification is analyzed for elemental signals including clicks, sines, and AM-FM sines. It is shown that with the use of some basic properties of linear systems, as well as FM-to-AM filter transduction, "perfect reconstruction" time-scaling filterbanks can be constructed for these elemental signal classes under certain conditions on the filterbank. Conditions for perfect reconstruction time-scaling are shown analytically for the uniform filterbank case, while empirically for the nonuniform constant-Q (gammatone) case. Extension of perfect reconstruction to multi-components signals is shown to require both filterbank and signal-dependent conditions and indicates the need for a more complete theory of "perfect reconstruction" time-scaling filterbanks.

An approach to the joint estimation of sine-wave amplitude modulation (AM) and frequency modulation (FM) is described based on the transduction of frequency modulation into amplitude modulation by linear filters, being motivated by the hypothesis that the auditory system uses a similar transduction mechanism in measuring sine-wave FM. An AM-FM estimation algorithm is described that uses the amplitude envelope of the output of two transduction filters of piecewise-linear spectral shape. The piecewise-linear constraint is then relaxed, allowing a wider class of transduction-filter pairs for AM-FM separation under a monotonicity constraint on the filters' quotient. The particular case of Gaussian filters is shown to yield a closed-form solution to AM-FM estimation while gammatone filters, used as a simplified model of auditory filters, and measured auditory filters, although not leading to a solution in a closed form, provide for iterative AM-FM estimation. Solution stability analysis and error evaluation are performed and the FM transduction method is compared with the energy separation algorithm, based on the Teager energy operator, and the Hilbert transform method for AM-FM estimation. Finally, a generalization to two-dimensional (2-D) filters is described.

A new approach to the joint estimation of sine-wave amplitude modulation (AM) and frequency modulation (FM) is presented based on the transduction of frequency modulation into amplitude modulation by digital filters, being motivated by the hypothesis that the auditory front end uses a similar transduction mechanism in measuring sine-wave FM. An AM-FM estimation algorithm is derived which uses the amplitude envelope of the output of two transduction filters of piecewise-linear spectral shape. The piecewise-linear constraint is then relaxed, allowing a wider class of transduction filters for AM-FM separation. The particular class of Gaussian filters is shown to yield a closed form solution to AM-FM estimation. Solution stability analysis and error evaluation are performed, and the FM transduction method is shown to typically compare favorably with the Teager energy operator and the Hilbert transform for AM-FM estimation. Finally, the amenability of cochlear gammatone-filter pairs to separate AM and FM is demonstrated.

A new approach to time-scale expansion of short-duration complex acoustic signals is introduced. Using a subband signal representation, channel phases are selected to preserve a desired time-scaled temporal envelope. The phase representation is derived from locations of events that occur within filter bank outputs. A frame-based generalization of the method imposes phase consistency across consecutive synthesis frames. The method is applied to synthetic and actual complex acoustic signals consisting of closely spaced rapidly damped sine waves. Time-frequency resolution limitations are discussed.