Equalizer

What is and Equalizer for?

Equalizers are intended to correct the tonal balance in the audio, by adjusting only certain bands of frequencies (low, mid, high, or Bass, Mid, Treble). These ranges can either be amplified (turned up) or attenuated (turned down) independently of each other. Using an equalizer can either bring out the subtleties otherwise lost in the audio recording, or reduce the tonal imperfections in the music or audio program.

An example of this is in voice-only recordings. When there is a background hiss or hum under the voice; a Vocal Equalizer preset is intended to boost the primary tones of the human voice (turning up the bands of frequencies where the human voice has the most presence), while at the same time, turning down bands above and below the human voice range. The result is the clarification of the voice.

One key fact about consumer usage of EQs is that people often mistake them for being “enhancers” of an inferior audio system. They use bass boost and other presets such as “Rock” or “Loudness” as a means to make a weak component system sound better. Although this is the case in many consumer electronics systems with mismatched components, it’s really not the proper application for EQ. EQ is meant to correct the tone of audio material, not inferior equipment.

Types of Equalizers

The Shelving Filter Equalizer - This is the conventional tone control most used on home stereo systems and basic sound system mixer/amplifiers. Typically, the bass control affects frequencies around 100 Hertz (Hz) and below, and the treble control affects frequencies around 10,000 Hz and above.

The Parametric Equalizer - This is a sophisticated tool which allows you to adjust not only the amount of cut or boost, but you can also control what frequency is most affected. To make it more complicated, you can also adjust the bandwidth (the amount of frequencies which are affected by the equalizer).

The Graphic Equalizer - The controls are constructed so you can "graphically" see how the individual filters are set. There are three basic types of graphic equalizers. The difference is mainly in the number of filters in the equalizer. The smallest is the octave band equalizer, which is usually nine to ten filters with their center frequencies set one octave apart. The two-third octave band equalizer has more filters which are spaced 2/3 of an octave apart. There are usually 15 controls on this equalizer. The 1/3 octave band equalizer provides the highest degree of control, where the center frequencies are spaced only 1/3 of an octave apart. This device usually has 27 to 30 controls to help you accurately shape and control the sound of your system.

What should I use an Equalizer for?

Equalization of the Loudspeaker System

The loudspeakers may not reproduce an even (or flat) frequency response. In other words, certain frequencies are louder or softer than others. This can produce sound which is unnatural, harsh, or doesn't have enough bass. The equalizer can be used to electronically smooth out the response and make the loudspeaker sound better.

Compensation for Loudspeaker Placement

The mounting position of the loudspeaker can greatly affect the sound you hear. Positioning the loudspeaker in a corner or by a ceiling will increase the bass response of the loudspeaker. The equalizer can be adjusted to provide a more even response from the loudspeaker/room system.

Compensation for Room Acoustics

Equalizers cannot alter a room's reverberation time characteristics or remove the unwanted echoes that can destroy clarity and intelligibility. The equalizer can't fix the acoustical problems caused by the physical construction and geometry of a room, but it can help relieve some of the symptoms. For instance, if the area is very “boomy”, the equalizer will probably improve the clarity of the sound if the bass frequencies are reduced.

To Reduce Feedback

The 1/3 octave band or parametric equalizer is one tool that can be used to minimize feedback. In use, the individual filters are turned down small amounts at the same frequencies which are feeding back. The system could feed back at that frequency because one of the sound system components has an uneven response at 500 Hz. Perhaps the microphone picks up 500 Hz a little stronger, or the loudspeaker puts out a little more volume at 500 Hz. Whatever the cause, you can electronically turn down that frequency with the 500 Hz control on your 1/3 octave band equalizer. The system is no longer as sensitive at 500 Hz and the feedback will stop. You can now increase the volume and look for the next problem spot.

Additional Applications

Some other applications of the equalizer would include compensation for the microphone characteristics and positioning, to improve speech clarity and intelligibility, and even create special effects.

Knowledgebase Terms

CUTOFF FREQUENCY - The frequency at which a high or low frequency EQ section starts to take effect. Also referred to as turnover frequency.

SLOPE - The rate at which a high or low frequency EQ section reduces the level above or below the cutoff frequency. Usually 6, 12, 18 or 24dB/octave.

PASS BAND - The frequency range that is allowed through.

STOP BAND - The frequency range that is attenuated.

FILTER - An EQ section of the following types:

HIGH PASS FILTER - A filter section that reduces low frequencies.

LOW PASS FILTER - A filter section that reduces high frequencies.

BAND PASS FILTER - A filter section that reduces both high and low frequencies.

NOTCH FILTER - A filter that cuts out a very narrow range of frequencies.

GAIN - The amount of boost or cut applied by the equalizer.

Q - How broad or narrow the range of frequencies that is affected.

SWEEP MID - A middle frequency EQ section with controls for frequency and gain.

PARAMETRIC EQ - A type of equalizer with controls for Frequency, Q, and Gain.

GRAPHIC EQ - An equalizer with a number of slider controls set on octave or third octave frequency centers.

BELL - An EQ with a peak in its response.

SHELF - A high or low frequency EQ where the response extends from the set or selected frequency to the highest or lowest frequency in the audio range.

HF - High frequencies

LF - Low frequencies

MID - Midrange frequencies