Teach Me Audio

Equalizers

An equalizer adjusts the relative amplitudes of frequencies within the audible spectrum, shaping the overall tone and balance of sound. Explore how EQ enhances audio clarity and impact.

equalizer
Figure 1 - Typical hardware graphic equalizer

Adjusting the amplitudes of different frequencies changes the the unique tone of an instrument or mix. The most common frequency ranges altered by an equalizer are:

  • Bass
  • Mid-range
  • Treble

Equalization may need to be applied to a single recorded channel, to a group of channels, or an entire mix.

Types of Equalizers

There are four primary types of equalizer, each offering different levels of control:

Filters

The filter is the simplest type of equalizer, typically controlled by a single button or knob. There are three main types:

  • Low Pass Filter: Reduces frequencies above a set threshold, rolling off high frequencies.
  • High Pass Filter: Reduces frequencies below a set threshold, removing low-end sounds.
  • Bandpass Filter: Allows frequencies within a set range to pass, cutting others.
Filters
Figure 2 - Typical filter plugin

Filters have limited adjustment and usually affect a fixed range of frequencies.

Shelving Equalizer

The shelving equalizer works on a fixed frequency range and allows for gain control. Types include:

  • Low-Frequency Shelf: Normally rolls off at around 150 Hz.
  • High-Frequency Shelf: Normally rolls off around 12 kHz.
Low frequency equalizer
Figure 3 - Low frequency equalizer, rolled off at 115 Hz
High frequency equalizer
Figure 4 - High frequency equalizer, rolled off at 12 kHz

Shelving EQs are often found in home audio systems as bass and treble controls.

Graphic Equalizer

The graphic equalizer affects a range of frequencies evenly spaced through the audio spectrum (20-20,000 Hz), as seen in figure 5 below.

equalizer
Figure 5 - Software graphic equalizer
  • Controls: Sliders adjust signal amplitude for each frequency band.
  • Applications: Basic models have 2-3 bands and are found on guitar amps and home audio systems; advanced models may offer 30+ bands.

Limitations: Graphic EQs lack control over individual bandwidths, making them less effective for precise mixing.

Parametric Equalizer

parametric-eq
Figure 6 - Software parametric equalizer

The parametric equalizer allows precise adjustment of specific frequencies, with control over the frequency center, gain, and bandwidth to shape the sound spectrum.

  • Center Frequency: Determines the primary frequency to adjust.
  • Gain Control: Cuts or boosts signal amplitude.
  • Bandwidth Control (Q): Defines the width of frequencies influenced, from narrow peaks (high Q) to wide curves (low Q).

This full-spectrum control makes the parametric EQ ideal for mixing.

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