Middle Frequency Equalizer with Parametric Feature

Figure 1 

The circuit was designed to produce an equalizer that would cater the middle frequency signals with limited and parametric attribute.

• Equalizer – a passive or an active electronic element or circuits (like tone control) used for the reason of altering or flattening the frequency response characteristics of a system
• NE5532 – an internally compensated low noise dual operational amplifier with features such as full power bandwidth up to 140 KHz, input noise voltage of 8 nV, common mode rejection ratio, 9 V/us slew rate, high DC voltage gain, 32 V peak to peak voltage swing, wide supply voltage range from 3 V to 12 V, unity gain bandwidth at 10 MHz, and internal frequency compensation

The circuit can be used with any other audio circuit although it is normally connected to the microphone line balance unit. The circuit is comprised of two parts having a typical bass and treble circuit and a parametric circuit of mid frequencies. The circuit of the equalizer will take an audio output, and manually boosting or attenuating the amplitude by adjusting the two channels consisting of the bass with 20 HZ to 1 KHz and the treble with 1 KHz to 20 KHz. With 18 dB at 20 KHz, the high frequencies are regulated by R2 while the low frequencies are regulated by R5. At 15 dB, the middle frequency is regulated by R11 while the center of middle frequency at 200 Hz to 6 KHz is regulated by R10.

The level of the bass is controlled below a certain frequency while treble changes are made above a certain frequency. The equalization of mid frequency rises to a maximum at its center frequency which will quickly fall off again to a flat response while passing all frequencies. Nevertheless, the output of the equalizer circuit provides sufficient amplification to a speaker.

Figure 2 

One of the handiest audio tools for videography is the use of the equalizer to eliminate problems in some soundtracks. They can be located in a rack full of audio processors or in an audio mixer. They are used to assist in the elimination of unwanted noise, capture a horrible audio buzz, to control the audio tonal balance, and decrease the tape hiss. This type of equalizer circuit is commonly used in stereo receivers and small audio mixers.

Source:users.otenet.gr/~athsam/parametric_mid_eq.htm