Tone control allows listeners to adjust sound to their liking. It also enables them to compensate for recording deficiencies,
hearing impairments, room acoustics or shortcomings with playback equipment. For example, older people with hearing problems may
want to increase the loudness of high pitch sounds they have difficulty hearing. Tone control is also used to adjust an audio
signal during recording. For instance, if the acoustics of the recording site cause it to
absorb some frequencies more than others, tone control can be used to amplify or "boost" the frequencies the room dampens.
In their most basic form, tone control circuits attenuate the high or low frequencies of the signal. This is called treble or bass "cut".
The simplest tone control circuits are passive circuits which utilize only resistors and capacitors or inductors. They rely on the property
of capacitive reactance or inductive reactance to inhibit or enhance an AC signal, in a frequency-dependent manner. Active tone controls
may also amplify or "boost" certain frequencies. More elaborate tone control circuits can boost or attenuate the middle range of frequencies.
Graphic equalizers used for tone control provide independent elevation or attenuation of individual bands of frequencies. Wide frequency
range graphic equalizers of high resolution can provide elevation or attenuation in 1/3 octave bands spanning from approximately 30 Hz to
18 kHz. Parametric equalizers can control not only the amount of boost and cut but also the specific frequency at which the boost and cut
takes place and the range of frequencies (bandwidth) affected.
Elaborate circuits may also use amplifiers. The most modern analog units use operational amplifiers, resistors and capacitors, abandoning
inductors because of their size and sensitivity to ubiquitous electromagnetic interference. Historically, tone control was achieved via
analog electronics, and most tone control circuits produced today still
use the analog process. Nonetheless, digital approaches are increasingly being implemented through the use of digital signal processing.