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A filter selectively attenuates or boosts specific frequency ranges in a signal

Concept L1Foundations B · Sound design & synthesis D · Mixing, mastering & loudness

A filter is a signal processing device that acts on the frequency content of a signal: it attenuates or boosts some frequencies and passes others. The four basic types are lowpass (passes lows, cuts highs), highpass (passes highs, cuts lows), bandpass (passes a band, cuts outside it), and bandreject/notch (cuts a band, passes outside it). A filter cannot boost or cut frequency components that are not present in the input — you can only shape what already exists. A filter is characterized by its cutoff frequency and its resonance (Q factor).

Examples

Applying a lowpass filter with cutoff 500 Hz to white noise produces a dark, muffled noise with only low frequencies. The same filter on a sawtooth at 100 Hz removes upper harmonics, making it sound rounder.

Assessment

Why does it not make sense to use a filter to boost frequencies around 50 Hz when processing a soprano voice recording? What would you check before filtering any sound?

Prerequisites — understand these first

Don't confuse with

The four basic filter types are defined by which frequency region they pass or attenuate

Sources

“A filter is a signal processing device that acts selectively on some of the frequencies contained in a signal, applying attenuation or boost to them.”

corpus · electronic-music-and-sound-design-vol-1-cipriani-and-giri-of · chunk 22

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