Stereo graphic equalizer File:Graphic_equalizer.jpg 

Equalisation (EQ) is used in music production to adjust different frequencies in sound. It allows you to rectify any imperfections and maintain balance in your music. The first use of equalization was to rectify uneven frequency and response of telephone lines and electric systems. Much later on equalization was used in audio engineering to change frequency responses for live performances and recording. Engineers would also use filters to adjust the tone of the signal in the early days of radio broadcasting. In the 1930s,  RCA employee John Volkman introduced equalization to audio recording.  An audio playback device for movie theaters was equalized using that technology. 

In the 1950s, the first graphic equalizers were developed, allowing for more precise control over the frequency spectrum. Over time, EQ has become an essential tool in music production, used to shape the sound of individual instruments and entire mixes. They are used to correct or adjust the response of microphones, instruments, acoustics, or to combat feedback. It’s also used to eliminate unwanted sounds or make certain sounds more prominent. 

Citations

Equalization (audio) (2023) Wikipedia. Available at: https://en.wikipedia.org/wiki/Equalization_(audio)#:~:text=Variable%20equalization%20in%20audio%20reproduction,equalizer%20to%20use%20slide%20controls. (Accessed: 31 May 2023).