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Elimination of Common Signal from Stereo Audio

2016-01-06 22:39  
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Figure 1 

The circuit was designed to create a method by which the common signal can be removed from a musical song.

*Common Signal – used to give effect to the dynamic range of the audio signal *TL072 – a low noiseJFETinput operational amplifier with features such as common-mode input voltage range, high slew rate, operation without latch up, compensated internal frequency, high input impedance at theJFETinput stage, low noise, low total harmonic distortion, protected from output short circuit, low input bias and offset currents, wide common-mode and differential voltage ranges, and low power consumption

In the line of performing or listening to music, there are instances when voice is separated from the audio and may be eliminated in a musical song when required. Although the music is manufactured in the same level, two channels were used that made it possible to separate the sound from the voice. A mono signal without the voice can be obtained as an output if the common signal is eliminated between the two signals of channels. The only problem that can be encountered is the presence of bass instrument that comes along with the two channels. In this design of the circuit, the bass cannot be removed because it is added in the left and right signals.

The difference of signals and the low frequency signals are applied in the IC3A since it functions as an adder. A binary circuit adder functions as if two of its inputs were equal, without being referenced to the actual value of those inputs. The IC will act effectively as a connector where it coules two of its inputs direct to the sum and carry outputs. The circuit balancing is adjusted by the logarithmic potentiometer RV1 & RV2. To avoid undesirable phase drift in the input of the signal, there are no capacitors in the path of the signal. The quality of the components used in the circuit should also be taken into account during the design, like the resistors with precise value of 1% made of metal film.


Figure 2 

The theory behind this circuit is widely applied in karaoke tunes, which is well-known as videoke where the singers sing with the song with their own vocals. Unfortunately, some vocals cannot be removed at all when a stereo field is recorded in such a way that it prevents removal. Because of this, it might sound as if the vocal has not been completely removed. Other applications would be beneficial for kids who want to sing along with their favorite hits, although not suitable for professional use due to parameter issues. They can also be useful for kids taking vocal lessons.

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