The voice extractor designed here uses an audio op amp (741 or TL082). The purpose of the voice extractor is to remove the voice from a audio music. It finds application mainly when someone wants to remove the original voice of a music signal and put his own voice.
The op amp has been configured in differential amplifier mode. The differential amplifier is a kind of amplifier that amplifies the difference of the two inputs given to it (both inverting and non inverting inputs). But how does it remove the voice from the audio signal? Let’s discuss about the audio signal first.
In an audio signal, various audio frequencies are present. The frequency of every musical instrument is different from one another and when they are recorded, they all reside in the audio signal but with different frequencies. If the frequencies remain same they will make same sound. So the frequencies of each and every musical instrument including the voice should be different. But during recording of a musical song each instrument are sounded at a different time at the right and left channel. But the timing of the voice at both the left and right channels remains same. So when they are allowed to collide from opposite direction inside a differential amplifier, the voice gets cancelled as their amplitude are same at same time and only the music remains because they have different timings at the right and left channels.
It is to be noted here that the device will only work when both the right and left channels are connected at their terminals because the cancellation process occurs only when both the channels are allowed to collide inside the differential amplifier.
Two circuits are drawn, one with bipolar power supply and the other with unipolar power supply. Advantage of bipolar supply is that the output voltage swing will be greater and perfect quality of the audio waveform can be achieved. Still the big disadvantage is the power supply itself. Unipolar power supply can be portable but it gives a limited output voltage swing which may sometime (not always) degrade the audio waveform. So it is up to you which power supply is to use and accordingly the circuit has to be chosen.