A circuit or processor that modifies tone by blocking or passing a specific frequency range of the sound.
Filters work by allowing portions of the signal lower or higher than a given frequency to pass, and cutting the remainder of the signal. This frequency is referred to as the Cutoff Frequency. You can produce a relatively bright or darker sound by setting the Cutoff Frequency.
By adjusting the Resonance (which boosts the level of the signal in the area of the Cutoff Frequency), you can produce a distinctive "peaky" tone, making the sound brighter and harder.
From among various Filter types, Low Pass Filter is shown below.
On the tone generator block of the Electronic Musical Instrument, the sound signal output from the Pitch unit is to be processed by the Filter unit. The Effect block also has a dedicated filter unit.
Low Pass Filter