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Parametric Equalizers
Audio engineers use equalizers to accent or eliminate frequency ranges within a recording. The simplest equalizers are the "tone controls" found on stereo equipment. Usually, these tone controls only allow the user to raise or lower the loudness of two frequency bands, bass and treble. More sophisticated systems may offer a third band, midrange, as well. Tone controls do not allow adjustment of the frequency range, so they are only found on consumer or semi-professional equipment. Professional engineers look to two other types of equalizers, graphic and parametric, to improve a recording tone quality.
Graphic equalizers split the audio spectrum into many frequencies bands. The most common, 1/3 octave graphic equalizers, allow control of 31 bands of sound. The types of equalizers are most often found in sound reinforcement systems to tailor the sound of the loud speakers and suppress feedback and ringing. Smaller types of graphic equalizers, such as 2/3 and 1 octave models, affect broader bands of frequencies and offer less control of sound and feedback. These equalizers cost less and are often half the size of 1/3 octave equalizers, which is the main reason when they are bought. Like the tone controls mentioned above, graphic equalizers have fixed frequency bands, so they are rarely used in recording studios.

Parametric equalizers are the most versatile equalizers made. All four parameters of equalization (filter type, gain, center frequency and bandwidth) are adjustable so there are no ranges of sound that cannot be changed wit h them. The lesson and drills for this computer demonstration use parametric equalizers. The first two lessons feature hi pass and low pass filters to remove unwanted rumble and hiss. The nest two lessons demonstrate the shelving filters common in tone controls. Peaking (or bandpass) filters are next. They are useful to control ringing and feedback. Peaking filters have adjustable centers and widths, making them the most flexible type of equalizer setting.