An equalizer or EQ (also: Equaliser, English: to equalize, to equalize: align, equal: equal ) is a filter as an electronic component for sound design and equalization of audio frequencies, mainly music, or other frequency-based signals such as amplitude-modulated data signals. In German, described in the following devices are meant by this term often. For other meanings of the English word see equalization.


An equalizer is composed of a plurality of filters, by which the spectrum of the input signal can be processed. Usually an equalizer is used to correct nonlinear distortion of a signal. One can distinguish between different design and operating concepts.

  • Graphic Equalizer: Here is influenced each frequency band assigned to a separate controller (he has 26 to 33, typically 31 bands, each 1 /3 octave width), so that the course of the frequency correction is shown " graphic " by the regulators. This type of equalizers is also called x - band equalizer. The x stands for the number of controllers ( 31 controllers at a 31- band equalizer ).
  • Parametric Equalizer: This can be set ( parametric equalizer) for one or more frequency bands, the center frequency and the amplitude change ( peaking equalizer) and frequently also the filter Q ( according to the bandwidth ). This design is mainly found in mixers and effects units.

An equalizer ( a filter ) is usually active in the integrated amplifier in the negative feedback or is a passive amplifier upstream.

More and more are becoming increasingly important digital filters that are implemented as algorithms in programs for audio editing. Used computer or digital signal processors (DSPs ).



In hi-fi systems equalizers are used to improve or adapt to their own needs tone. It is often the true meaning of lay, namely the equalization of the signal in order linear frequency response, reversed (called the typical " U" shape of the position, also called " bathtub ": bass and treble emphasized mid lowered).

Concerts and Events

At concerts are equalizer, in addition to the equalization of individual sources (channels ), mainly used to the overall sound of the sound system ( " PA system " ) restate the localities. The reason: Each room affects the sound because of its geometry. By reflection of sound waves off the walls frequencies are amplified and / or attenuated ( interference). These " bumps " in the overall response of the system and the room will be "leveled " with the equalizer ( the sound check ). To this end, the equalizer in the so-called " total " (audio output at which is present the total signal ) is looped.

Sometimes this spectrum analyzers are used which measure the acoustic properties of the room and the equalizer and possibly other devices for influencing the sound system, such as crossovers or delay elements set specifically (integrated Hardware-/Softwarelösungen ). As a rule, however, is the fine tuning by an experienced sound technician or engineer, possibly with the assistance of a spectrum analyzer is preferred. (Must be because a large volume sonicated ) Especially in large concert halls with possibly many sound sources, the sound of the concert is very much dependent on the proper settings for these components.


To avoid disturbing feedback loops in the monitoring of live concerts, equalizers are often looped and thus lowered the affected frequencies in the signal to the monitoring system. This can also be done semi - automatically or fully automatically by means of so-called feedback Destroyer. In semiautomatic method, the device searches once the frequencies that cause feedback effects, and save the setting. This fully automated procedure is searched during the concert after running problem frequencies and this lowered narrow band, as they may change continuously (eg by different microphone positions, moves the singer ).

Both methods allow a higher volume monitoring, with the fully automatic has a greater effect. However, the disadvantage of this is to constantly changing frequency response of the monitor system, which can interfere with the sound impression.

Sound design

At concerts or recording sessions the individual audio signals are equalized by equalizer (eg acoustic problems during recording or non-linear frequency response of instruments and microphones ) as well as to the taste perceptions of the sound engineer / music producer adapted as a sound effect. It is also made sure that the individual signals are processed so that they blend harmoniously into the overall mixture (eg, by highlighting various characteristic frequencies of two similar signals, such as electric bass and bass drum ). Furthermore, EQ for the extreme change of signals used to restrict the processing by downstream devices to certain frequency ranges can, which are then re- mixed with the sum, or the effects of a detector input ( Key Chain) explicitly to frequency control ( Examples: De -esser; phaser drum track ).

Parametric Equalizer with great effect amplitude and high quality filters are also used directly for sound design. This results in flowing change the " cutoff " frequency characteristic, often artificially sounding pitch and resonance curves, which can range from sawing to twittering.


Even DJs use equalizers, which are integrated into the DJ mixers (also called blender ). These equalizers are often much easier. The most common variant here is the DJ mixer with three- band equalizer and a maximum reduction of the level by 32 dB. This is mainly due to the fact that the equalizer for live operation is operated and therefore should be kept as simple as possible to ensure fast operation. They usually do not consist of sliders ( faders), but are provided with knobs.

Designations and other examples

Examples of filters in audio engineering:

  • Height lock / Height Filter / High Cut / Treble Cut to the strong reduction ( English: to cut = cut ) to the high frequencies; ( academically: low pass) and
  • Deep Lock / Bass filter / low cut / bass cut / cut filter / junk filter for significantly lowering (English: to cut = cut ) of the low frequencies; ( academically: high-pass ).
  • Parametric or semiparametric filter / filter for Bell bell-shaped (english: bell bell = ) Change in a frequency band around a base frequency (English: center frequency). In semi- parametric equalizers can only the base frequency can be adjusted if (full) parametric EQ in addition the slope (Q).
  • Notch filter (English: notch = notch) to influence (usually decrease ) of a narrow frequency band by a steep-sided filter; (also called " Kill - filter " called ). This type is most commonly used to remove noise or acoustic feedback as well as for sound influenced by DJs and represents a special case of the bell-shaped parametric equalizer with extreme slope
  • Shelving / Hi- Shelf / Low Shelf Filter open on one side to lower / raise of ups and downs.

Furthermore, there is the main filter for the sound design ( for sound design ): the presence and absence filters filter. Part of this is the sound engineer slang known tub filter, which is mainly applied to the " Entmulmen " from " unclear " sound recordings.