A low-pass filter lets low-frequency sounds remain, and tries to eliminate frequencies above a specified cutoff frequency. For example, to eliminate high-pitched scratching sounds, use this with the high frequency set to 12000 Hz.

A high-pass filter lets high-frequency sounds remain, and tries to eliminate frequencies above a specified cutoff frequency. If the entire wave is above or below the zero-line, and you want to bring it closer to zero, try doing a high-pass filter with the lowest frequency allowed set to 10.

A band-pass filter lets sounds between the specified low and high cut-off frequencies remain, trying to eliminate frequencies outside this band.

A band-stop filter tries to eliminate sounds between the specified low and high cut-off frequencies. For example, use this to eliminate a 60 Hz hum, set the low frequency to 58, the high frequency to 62.