faust_recursive_circuits

faust_recursive_circuits.hs

-- faust
-- import("stdfaust.lib");
-- lowpass(cf, x) = y
--     letrec {
--         'y = b0 * x - a1 * y;
--     }
--         with {
--             b0 = 1 + a1;
--             a1 = exp(-w(cf)) * -1;
--             w(f) = 2 * ma.PI * f / ma.SR;
--         };
-- process = lowpass;

-- precompute the filter coefficients outside the filtering function, especially since they do not change unless the cutoff
-- frequency changes. This is more efficient when processing a large batch of samples, as it avoids recalculating 
-- the coefficients for each sample.

module Main where

import Data.Vector (Vector, scanl')
import qualified Data.Vector as V

samplingRate :: Double
samplingRate = 48000.0  

coefficients :: Double -> (Double, Double)
coefficients cf = let w = 2 * pi * cf / samplingRate
                      a1 = -exp(-w)
                  in (1 + a1, a1)

lowpass :: Double -> Double -> Vector Double -> Vector Double
lowpass b0 a1 = scanl' (\y x -> b0 * x - a1 * y) 0

main :: IO ()
main = do
  let cf = 1000  
      (b0, a1) = coefficients cf
      samples = V.fromList [0.0, 1.0, 0.5, 0.2, 0.1, 0.0] 
      filteredSamples = lowpass b0 a1 samples
  print filteredSamples