----------------------------------------------------------------------------- -- | -- Module : DSP.Multirate.Polyphase -- Copyright : (c) Matthew Donadio 2003 -- License : GPL -- -- Maintainer : m.p.donadio@ieee.org -- Stability : experimental -- Portability : portable -- -- Polyphase interpolators and decimators -- -- Reference: C&R -- ----------------------------------------------------------------------------- module DSP.Multirate.Polyphase (poly_interp) where import Data.List (transpose) import Data.Array import DSP.Filter.FIR.FIR -- mkpoly turns a single filter into a list of l subfilters mkpoly :: Num a => Array Int a -> Int -> Int -> Array Int a mkpoly h l k = listArray (0,m) [ h!(k+n*l) | n <- [0..m] ] where m = ((snd \$ bounds h) + 1) `div` l - 1 -- | Polyphase interpolator poly_interp :: (Num a, Eq a) => Int -- ^ L -> Array Int a -- ^ h[n] -> [a] -- ^ x[n] -> [a] -- ^ y[n] poly_interp l h x = concat \$ transpose y where g = map (fir . mkpoly h l) [0..(l-1)] y = map (\$ x) g {- gZipWith :: Eq a => (a -> a -> a) -> [[a]] -> [a] gZipWith f xs | any (== []) xs = [] | otherwise = foldl1 f (map head xs) : gZipWith f (map tail xs) poly_decim :: Num a => Int -> Array Int a -> [a] -> [a] poly_decim l h x = gZipWith (+) g where g = map (fir . mkpoly h l) [0..(l-1)] Test > h :: Array Int Double > h = listArray (0,15) [1..16] > x :: [Double] > x = [ 1, 0, 0, 0 ] -}