Wave digital filters (WDFs) are modeled after classical filters, preferably in lattice or ladder configurations or generalizations thereof. They have very good properties concerning coefficient accuracy requirements, dynamic range, and especially all aspects of stability under finite-arithmetic conditions. A detailed review of WDF theory is given. For this several goals are set: to offer an introduction for those not familiar with the subject, to stress practical aspects in order to serve as a guide for those wanting to design or apply WDFs, and to give insight into the broad range of aspects of WDF theory and its many relationships with other areas, especially in the signal-processing field. Correspondingly, mathematical analyses are included only if necessary for gaining essential insight, while for all details of more special nature reference is made to existing literature.

Wave digital filters: Theory and practice

There has been a constant interest in the design and implementation of digital filters with variable characteristics for different applications. In this article an attempt is made to review and systematize all known structures and methods of design of such filters. First the basic theory of the variable digital filters is introduced. Then FIR and IIR realizations with real and complex coefficients are considered, the known results for multidimensional variable filters are discussed and finally, typical implementations are overviewed. Recommendations for applications in different situations are given and unresolved problems are pointed out. This work is basically a review, but some of our original results are also included.

Variable Digital Filters

Tunable digital frequency response equalization filters, which feature adjustable gain at specified frequencies while leaving the remainder of the spectrum unaffected, are advanced. The filter structure is such that the frequency response parameters are independently related to the multiplier coefficients, which permits simple frequency response adjustment by varying the coefficient values. The resulting structure exhibits low coefficient sensitivity characteristics.

Tunable digital frequency response equalization filters

A new method for changing the cut-off frequency of infinite impulse response (IIR) digital filters with a single parameter is derived. the method is based on the use of the Taylor series expansion of the lowpass-to-lowpass frequency transformation. the filter structure is a parallel connection of real or complex allpass sections. the tuning range is several octaves for narrowband filters. By taking also the complementary output, a power-complementary filter pair with tunable crossover frequency is readily obtained. Tunable centre frequency and bandwidth are obtained by incorporating a special lowpass-to-bandpass transformation into the structure. Design examples and a description of a signal processor implementation are included.

Design of recursive digital filters with variable characteristics

A new type of second-order digital parametric equalizer is proposed whose frequency response matches closely that of its analog counterpart throughout the Nyquist interval and does not suffer from the prewarping effect of the bilinear transformation near the Nyquist frequency. Closed-form design equations and direct-form and lattice realizations are derived.

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Digital Parametric Equalizer Design with Prescribed Nyquist-Frequency Gain

This paper presents a method of designing wave digital bandpass (BP) and bandstop (BS) filters whereby the center frequency and bandwidth can be independently controlled by simply changing the multiplier values. Also given are the canonic realizations for the BP and BS wave digital filters. This method of designing BP and BS wave digital filter results in a saving of coefficient registers.

M.N.S. Swamy

Papers

Digital bandpass and bandstop filters with variable center frequency and bandwidth