Filtertypes

Filtertypes refers to classes of filters used to modify signals by attenuating unwanted frequency components and, in some designs, boosting others. Filters are described by a transfer function and by their magnitude and phase responses, which specify how different frequencies are scaled and delayed.

The basic passband-based categories are: low-pass, which passes low frequencies and attenuates high ones; high-pass, which passes high frequencies and attenuates low ones; band-pass, which passes a finite frequency range; and band-stop (notch), which attenuates a chosen range while passing others. All-pass filters pass all frequencies with unity magnitude but alter phase.

Other types include shelving filters, which boost or cut all frequencies below or above a break frequency; notch filters for narrow-band rejection; and peaking or resonant filters that shape a specified band. In digital and analog contexts, filters are further described by their impulse-response structure (FIR or IIR) and by design goals such as linear phase.

Implementation considerations distinguish analog and digital realizations. Digital filters are commonly implemented as finite-impulse-response (FIR) or infinite-impulse-response (IIR) structures, with order and coefficient choices impacting transition sharpness, passband ripple, stopband attenuation, and phase behavior.

Applications span audio processing, communications, control systems, and image processing. In images, low-pass filters blur or denoise, while high-pass filters emphasize edges. Filter design aims to meet specifications such as cutoff frequency, transition bandwidth, allowable ripple, and whether linear phase is required.