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An electronic device or piece of software that alters sound waves is known as a signal processor. One very common signal processor is an audio equalizer. An audio equalizer raises and lowers the strength of a sound wave. The goal of equalization (EQ) is to help achieve a good mix of sound that allows all instruments and vocals to sound good together.
Equalization can target part of a sound based on the frequency amplitude, or height, of the sound wave. For example, if the bass drum is drowning out the cymbals in an audio mix, an audio equalizer can make the cymbals sound louder. In this case the sound engineer will choose to raise the strength, or gain, of the high frequencies that make up the cymbal’s sound. The engineer may also choose to decrease the gain of the very low frequencies in the bass drum track.
Removing sound is another equalization goal. A bass drum microphone may also pick up and record sounds from the cymbals. The problem of recording unwanted sounds is known as bleeding or leakage. To get a cleaner bass drum track, an engineer can use an audio equalizer to lower the high frequencies on the bass drum track. This effectively removes the cymbal leakage.
An audio equalizer can be part of an audio mixer, a stand-alone piece of electronic hardware, or a software application. Audio equalizers inside a mixer usually have controls for three bands of frequencies including high, mid-range, and low. These equalizers make it easy to use EQ during the recording process.
Several varieties of stand-alone audio equalizers can be used that target sounds based on different characteristics. A sound is generally made up of a range of frequencies known as the bandwidth. The center frequency is in the middle of the bandwidth. A peaking, or parametric, equalizer includes controls that can affect a sound wave’s gain, bandwidth, and center frequency.
A graphic equalizer usually includes several controls, or sliders, to manipulate several frequency ranges. These equalizers also illustrate sounds levels with a row of lights for each frequency range. These lights make it easier for an engineer to see which frequencies need to be adjusted to get a good sound mix.
Specialty software applications, often called plug-ins, that perform EQ are also widely available. Usually, the EQ software works with, or plugs in to, a larger sound recording application. The engineer can use an audio equalizer plug-in on a certain track, part of track, or all of the tracks in a recorded song.
All signal processing adds noise, or unwanted sound, to an audio track. For this reason, engineers may want to limit the amount of equalization needed during the mixing process. In place of EQ, an engineer can try to achieve a better mix of sound during the recording process by using different microphones, moving microphones, or recording various instruments during separate recording sessions.
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