Showing papers on "Quadrature mirror filter published in 1979"

Sub-band coder design incorporating quadrature filters and pitch prediction

Abstract: In this paper we discuss several new issues in the design of sub-band coders for low bit-rate speech coding. We use unequally spaced filter banks to match perceptual criteria for speech. In particular, we apply quadrature mirror filter techniques to provide cancellation of aliasing between sub-bands, thus permitting a reduction in the order of the filters. Preliminary investigations have been made into the use of pitch prediction within the sub-bands. Designs will be discussed for coder bit rates of 9.6 and 16 kb/s and their performance will be compared with earlier sub-band coder designs.

A maximally flat filter design algorithm for quadrature mirror filters (QMF)

Abstract: This paper describes a numerical procedure for designing maximally flat quadrature mirror filters (QMF) for use in split-band voice coding systems. As originally proposed by Croisier, et al, the FIR filters used in QMF structures must possess certain characteristics in order to achieve perfect reconstruction of a decomposed signal (1). These constraints require that the elementary filter response exhibit an odd symmetric property about the quarter-band frequency and the 3 dB point. In addition, the filter must exhibit highly attenuated stop bands in order to orthogonalize the adjacent subbands. A filter design algorithm proposed by Herrman has been implemented and structured to satisfy these QMF constraints (2). A detailed analysis of this maximally flat FIR approach to QMF design will be discussed along with the problems associated with its implementation.