Showing papers on "Quadrature mirror filter published in 1987"

Quadrature mirror filter banks, M-band extensions and perfect-reconstruction techniques

Abstract: In this paper, quadrature mirror filters (QMF) are reviewed. After a brief introduction to multirate building blocks, the two-band QMF bank is discussed. Various distortions caused by the structure, and methods to eliminate these distortions are outlined. Perfect-reconstruction structures for the two-band case are reviewed, and the results are extended to the case of arbitrary number of channels. The relation between perfect-reconstruction QMF banks and the concept of losslessness in transfers-matrices is indicated. New lattice structures are presented, which perform the perfect reconstruction, sometimes even under coefficient quantization.

Theory and design of M-channel maximally decimated quadrature mirror filters with arbitrary M, having the perfect-reconstruction property

Abstract: Based on the concept of losslessness in digital filter structures, this paper derives a general class of maximally decimated M-channel quadrature mirror filter banks that lead to perfect reconstruction. The perfect-reconstruction property guarantees that the reconstructed signal \hat{x} (n) is a delayed version of the input signal x (n), i.e., \hat{x} (n) = x (n - n_{0}) . It is shown that such a property can be satisfied if the alias component matrix (AC matrix for short) is unitary on the unit circle of the z plane. The number of channels M is arbitrary, and when M is two, the results reduce to certain recently reported 2-channel perfect-reconstruction QMF structures. A procedure, based on recently reported FIR cascaded-lattice structures, is presented for optimal design of such FIR M-channel filter banks. Design examples are included.

Truncated subband coding of images

Abstract: Image data is analyzed in a number of iterated analysis procedures, using two-dimensional quadrature mirror filters to separate low-pass spatial filter response component and three differently oriented high-pass spatial filter response components, which filter response components are decimated in both dimensions. The high-pass filter response components are coded as is. The low-pass filter response component is coded as is only in the last iteration; in the earlier analysis procedures the low-pass filter response component provides the input data for the secceeding analysis procedure.

Quadrature mirror filters with staggered-phase subsampling

Abstract: By staggering the phases of the decimations of the subbands in a quadrature mirror filter bank odd-tap kernels may be usefully employed.

Perfect reconstruction QMF banks for two-dimensional applications

Abstract: A theory is outlined whereby it is possible to design a M \times N channel two-dimensional quadrature mirror filter bank which has perfect reconstruction property. Such a property ensures freedom from aliasing, amplitude distortion, and phase distortion. The method is based on a simple property of certain transfer matrices, namely the losslessness property.

Digital FM demodulator using digital quadrature filter

Abstract: A frequency-modulated digital signal demodulator includes a digital quadrature filter having n elements arranged in cascade, each delaying the input signal by a value T E =1/F E , where F E is the sampling frequency, a number of channels arranged in parallel with the cascade arrangement of delay elements, each channel having a multiplier for multiplying by a given coefficient, a first and a second summing circuit for summing the respective output signals of said multipliers, the output signals of the two summing circuits constituting the quadrature output signals of the filter and being referred to as reference and phase-shifted signals. At the output of the filter a circuit for calculating the instantaneous phase φ n of successive signal samples is provided. In order to provide a demodulator with an improved threshold and with a digital quadrature filter having an identical amplitude-frequency response for the quadrature channels and, with a view to reducing the cost, a smaller number of electronic components than that in prior art arrangements is used. The demodulator according to the invention includes, in parallel with the circuit for calculating the instantaenous phase, a circuit for evaluating the signal-to-noise ratio which is provided with a control circuit for modifying the coefficients of the quadrature filter when said ratio drops below a given threshold.

Some results on two-dimensional pseudoquadrature mirror filters

Abstract: One-dimensional (1-D) pseudoquadrature mirror filters (PQMF's) have been introduced as a generalization of quadrature mirror, filter (QMF) concepts. Use of such filters allows one to split directly the spectrum of an input signal into N equally spaced subbands which can be decimated by N: 1 , then interpolated and recombined to reproduce the original signal. In this paper, a detailed derivation of conditions specifying 2-D PQMF design constraints for a distortion-free (i.e., aliasing and amplitude distortions) reconstruction of the original signal are obtained. Potential applications for such filters include efficient subband coding of digital pictures.

A note on general parallel QMF banks

Abstract: Two issues concerning alias-free, parallel, quadrature mirror filter (QMF) banks are addressed in this correspondence. First, a property concerning alias-free analysis/synthesis systems is established; second, a scheme is proposed, by which a synthesis bank can be modified in order to take care of aliasing errors caused by linear channel-distortion in a simple manner. Applications of the stated results are outlined.

Complementary filtering technique for subband speech coder design

Abstract: This paper presents a new filtering scheme for splitting speech signals into subbands which results in no aliasing problem when the subband signals are sub-sampled and recombined. The highpass and lowpass filters are an odd-length complementary linear phase filter pair. As a consequence, the highpass filter output can be obtained by subtracting the lowpass filter output from the appropriately delayed input. This produces a factor-of-two reduction in the computation load when compared to the conventional even-length quadrature mirror filter. Another factor-of-two saving in computation load can be gained by using halfband lowpass filters whose every other coefficient is zero. Furthermore, the filters can be designed using well known minimax optimization techniques such as the Remez exchange algorithm and integer programming.