Lagrange interpolator filters and binomial windows

The filter produced by a type 2 polyphase decomposition of Lagrange bank fi lters is examined and found to have several problems. The filter can be con sidered to be the product of the sine function and a window that has coeffi cients that are related to the binomial distribution. This window (which is shown to be often asymmetrical) was found to cause high sidelobes in the s topband of the reconstructed filter. A new window is defined that uses the binomial distribution directly to produce window coefficients. An efficient algorithm is presented to generate these coefficients. The window works we ll as an interpolator, having better stopband performance than the Lagrange method. The window itself appears also to be useful in non-interpolation a pplications, in that it is tunable with similar performance to the Kaiser a nd Chebychev windows. (C) 1999 Elsevier Science B.V. All rights reserved.