Tone control circuit

Under tone controls or EQ (English: tone control ) is the electronic filter circuits in radios, amplifiers and other audio equipment, as well as electrically amplifiable musical instruments such as electric guitar and electric bass, with which the user can adjust the timbre of the audio playback.

Technically precise, one should speak of tone controls or sound adjustment, since there is no control mechanism exists, but only manual controls. The control term is used mainly in the use of language.

Variants

Over time, the circuits have a hand in the development effort, which drew more and more in general affordable regions. On the other hand, the demands changed in view of the existing signal quality and the technical possibilities.

Fade

The simplest variant is a low pass filter for attenuation of high frequencies. In the early days of broadcasting with a predominant medium wave reception and receivers with electron tubes, there was immense noise by superimposed noise and hiss. This could be eliminated with a tone control, to a certain degree. The user can adjust the potentiometer with a single degree of filtering. For circuit implementation extends next to the potentiometer has a single capacitor.

Sound balance

Here the user can set with a single potentiometer whether rather the depths or heights should preferably be allowed through.

Middle Dreher

As a " mid- turner " was a kind of sound balance ( see above) referred to, which was used in movies and recordings. In this case, a center frequency of 800 Hz was left, while the frequencies are 60 Hz and 10 kHz counter lowered or raised.

Bass and treble controls

This is the most widely used to date version. The user has two potentiometers are available. With the one he can lift or dampen the depth range, with the other the height range. Circuitry, the setting with simple RC network is realized. Even more efficient are such filters when they are inserted in the feedback path of an amplifier circuit. The crossing point between treble and bass controls is often lower than 1 kHz, because according to the amplitude statistics of the music, the sound center is rather something deeper; ( 600 to 800 Hz). The center frequency of the Hi- frequency range below 1 kHz. Are used mainly treble and bass controls by Peter J. Baxandall, the " shelving filters" as " Baxandall tone controls" or "shelf filter" are known; in the jargon also called shelving.

Depth, presence and treble controls

Here the two adjusters, a third is added as an adjustable presence filter for the mid-frequency range for bass and treble. Therefore, this adjuster is sometimes labeled as " mid control ". This variant was used only in a few, mostly higher-quality devices.

Equalizer

With an equalizer, the frequency range in many individually adjustable frequency bands is divided, or there are filters with variable slope is available ( parametric equalizer ). This allows to adapt to the individual requirements and hearing the music consumption, or even a specific change in the sound image in the studio. In a graphic equalizer, the adjusters are designed as a slider, so that its position is directly gives a broad picture of the current frequency response.

Presets

Apart from the above analog adjusters there - mostly addition - also switchable presets, the frequency responses of typical use cases such as "Jazz ", " language", " orchestra ", and so completing the configuration, without the user having all setter needs to adapt itself.

Stereo

In a stereo system, these filters must be installed in parallel in each channel. As a potentiometer for adjustment then tandem versions are used. Even higher channel numbers like 5.1 surround sound in this way are no longer feasible.

Digital technology

In many devices - Example: car radio - the audio is now exclusively digital processing along the entire signal chain. The tone control is likewise implemented by digital filtering algorithms in digital signal processors ( DSPs). Also expansion of example 5.1 channels ( surround sound ) in this context means no particular overhead. The basic concept with separate bass and treble adjusters and possibly presets but it is used more because it is proven and can be operated intuitively. However, even an equalizer can be implemented relatively easily, only the operator is then more complex.