A filter can emphasize or de-emphasize certain parts of the frequency spectrum of a sound. Various kinds of filters are used to achieve different sound effects.
Low-pass filter : Eliminates frequencies above a specified threshold.
High-pass filter : Eliminates frequencies below a specified threshold.
Band-pass filter : Cuts off lows and highs ( An example is the telephone. In a telephone the very high frequencies and the very low frequencies are eliminated )
Low-shelf filter : This affects the amount of bass in a sound.