A philtre (usually linear,) in discrete time, that is normally implemented through digital electronic computation. Note: Digital philtres differ from continuous time philtres only in application. The parameters of digital philtres are generally more stable than the parameters of commonly used analogue (continuous) filters. Digital philtres can be applied as optimal estimators. Commonly used forms are finite impulse response (FIR) and infinite impulse response (IIR. )