synthesizer-core- Audio signal processing coded in Haskell: Low level part

Portabilityrequires multi-parameter type classes



State variable filter. One filter that generates lowpass, bandpass, highpass, bandlimit at once.



data Parameter a Source




k1 :: !a
k2 :: !a
ampIn :: !a
ampI1 :: !a
ampI2 :: !a
ampLimit :: !a

data Result a Source




highpass :: !a
bandpass :: !a
lowpass :: !a
bandlimit :: !a

parameter :: C a => Pole a -> Parameter aSource

The computation of the internal parameters is a bit complicated, but it fulfills the following properties:

  • At the resonance frequency the band pass has 180 degree phase shift. This is also approximately the frequency where the filter has maximum output. Even more important, this is the frequency where the band limit filter works.
  • At the resonance frequency highpass, lowpass, and bandpass amplify by the factor resonance.
  • The lowpass amplifies the frequency zero by factor 1.
  • The highpass amplifies the highest representable (Nyquist) frequency by the factor 1.
  • The bandlimit amplifies both frequency zero and Nyquist frequency by factor one and cancels the resonance frequency.

type State v = (v, v)Source

step :: (C a, C a v) => Parameter a -> v -> State (State v) (Result v)Source

Universal filter: Computes high pass, band pass, low pass in one go

modifierInit :: (C a, C a v) => Initialized (State v) (v, v) (Parameter a) v (Result v)Source

modifier :: (C a, C a v) => Simple (State v) (Parameter a) v (Result v)Source

causal :: (C a, C a v) => T (Parameter a, v) (Result v)Source

runInit :: (C a, C a v) => (v, v) -> T (Parameter a) -> T v -> T (Result v)Source

run :: (C a, C a v) => T (Parameter a) -> T v -> T (Result v)Source