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- No of Pages: 56

- No of Chapters: 5

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Introduction:

Abstract

Graphics equalizer (EQs) has been used since the 1920’s to adjust audio recording sound levels. The term “graphic equalizer” comes from the graph of signal gain versus frequency. An equalized signal has a flat line with no gain, in the context of audio; “equalizer” does not actually meant flattening the signal as in other applications, but more generally the adjustment of frequency domain characteristics that result in a non-equalized signal. This type of signal modification may have practical or aesthetic purpose.

The purpose of this project work is to build a graphics equalizer that may be used to “correct the response of microphones, instrument pick-ups, loudspeakers and hall acoustics”. Graphic equalizer can also dramatically change how someone hears audio or music, depending on the EQ settings. Because audio recorded in a studio contains frequency distortions inherent to the recording process and the acoustics of the room.

Typically, EQs control frequencies over a range of 20H2 to 20kH2, which is the range of human hearing.

Table of Content

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Introduction

This project work consists of a 10-band two channel graphic equalizer with bass and treble control left and right channels are operated on separately by ten sliders for each side. Moving the sliders up and down strengthens or weakens the energy in the corresponding frequency band. The sliders constitute part of an inverting band-pass filter that adds gain or attenuation over a certain range of frequencies, but has no effect outside the band. Each block of the equalizer circuiting acts on one or the ten frequency band; an inverting summer with unity gain recombines the individual signals. The output of the inventing summer serves as both the speaker and the display circuitry input to that the LED display will reflect any signal alterations. A repeated combination of a band-pass filter and peak detector for each frequency band comprises the display circuitry. The band-pass filter used has a higher quality factor and it removes any content outside the desired frequency band. Once it passes through the filer, the signal continues to the peak detector, where a capacitor follows the signal voltage until a maximum occurs. The capacitor holds the maximum until either a new maximum occurs or the transistor switches on and provides a discharge path to ground.

Moving the equalizer sliders modifies whatever audio signal enters the circuit. With the ranges and frequency bands available, the system can negate audio distortion effect such as microphone responses, instrument pick-ups, loudspeakers and room acoustics. The system can also alter the signal to make it sound as if it were recorded or played in a particular environment or way, such as a large hall or over old-time radio.