Signal Equalization

The equalizer allows you to filter a signal by increasing or reducing the gain in dB in predefined frequency bands. The signal energy can be strengthened or reduced in each frequency band.

With an equalizer you can vary the sound intensity from -75 dB to 25 dB in each frequency band (Hz) of the equalizer. The 3 equalizers available in Sound: Analysis and Specification are the Octave bands, the Third octave bands and the Bark bands equalizers:

Octave bands and Third octave bands equalizers follow standardized frequency band.

  • The Octave bands equalizer has ten frequency bands (also known as the Octave bands). One octave separates the lower and the upper frequencies of each frequency band. In Sound: Analysis and Specification, the central frequency is displayed at the bottom of each frequency band. For example, 31.8 Hz is the central frequency of the first frequency band.
  • The Third octave bands equalizer is similar to the Octave band equalizer, except that the Third octave band equalizer has 31 frequency bands. A 1/3 of an octave separates the lower and the upper frequencies of each frequency band. In Sound: Analysis and Specification, the central frequency is displayed at the bottom of each frequency band. For example, 20 Hz is the central frequency of the first frequency band.
Note: The filters used by the Equalizer are band filters with a very steep decay outside of the bands, resulting in steep frequency cutoffs between adjacent bands. These filters do not comply with the ANSI S1.1-1986 and IEC 61260 (1995-08) standards used for octave and 1/3 octave levels computation.

In the top block, named Narrow Bands, you can see the narrow band spectrum of a white noise (red curve) and the spectrum of the signal filtered through the Third Octave bands equalizer (blue curve) with the below equalizer settings. You can see on the fist curve that a gain of -20 dB is applied to the 1.25 kHz band, +20 dB to the band 1.6 kHz and -25 dB to the 2 kHz band.

On the bottom block, named Third Octave Bands, the same spectra are displayed in third octave bands. As you can see, the Third octave levels calculation does not reflect the third octave bands filters applied through the equalizer.

  • The Bark bands equalizer has 25 frequency bands (also known as the Bark bands). Bark bands are related to human hearing. Bark bands are also called Critical Bands. For more information about critical bands, refer to Bark scale and Critical Bands.