Equalizers use different types of filters to influence the sound.
Each filter type has a specific function and effect on the audio signal:

Bell filter

• Bell filters raise or lower a certain frequency and influence neighboring frequencies in the form of a bell curve.
  They are often used in parametric equalizers.
• Application: Ideal for precise adjustment of individual frequency ranges, e.g. boosting the presence range of a voice.

Low-pass filter (LPF)

• Low-pass filters (also known as high-cut filters) allow low frequencies to pass through and attenuate high frequencies.
  They are often used to remove noise or unwanted high frequencies.
• Use: In subwoofers and for reducing treble components in a mix.

High-pass filter (HPF)

• High-pass filters (also known as low-cut filters) allow high frequencies to pass through and attenuate low frequencies.
  They are often used to remove hum or low-frequency noise.
• Usage: Ideal for vocal recordings to eliminate pops and low frequency noise.

Band-pass filter (BPF)

• Band-pass filters only allow a certain frequency range to pass and attenuate frequencies above and below this range.
  These filters are crucial for isolating specific sound characteristics.
• Use: In crossovers of loudspeakers and for isolating certain instruments in a mix.

Notch filter

• Notch filters are extremely narrow-band filters that strongly attenuate a certain frequency.
  They are used to eliminate interfering frequencies without affecting the rest of the signal.
• Use: To remove feedback in live situations or resonances in recordings.

Shelving filter

• Shelving filters amplify or attenuate all frequencies above (high-shelf) or below (low-shelf) a certain cut-off frequency.
  They offer a smooth, gradual change in sound.
• Use: For overall sound adjustments in mixing and mastering processes.