How to build Remove common signal from stereo sound

Description

It many times happens, we want erase or decrease in a musical song, the voice of singer or some other sound that usually is written in same level and in the two channels. If we remove between them two signals of channels, we can take in the output a mono signal without the voice. Here exist a problem. The sound of bass instrument is also this written in two channels. With this circuit, the bass they can be not removed, if it is added in the signal [ L+R ], the signal [ L-R ]. The signal of low frequencies and the signal of difference, are applied in adder IC3Α. The balance between, regulated from the RV1-2. In the circuit do not exist capacitors in the line of signal, because add undesirable drift of phase in the signal of input. Attention should be given in the quality of materials of circuit. The resistors should anyhow be is precision 1% metal film. Elektor 8/89

Circuit diagram

Part List

All the Resistors is 1/4W 1% metal film

circuit from http://users.otenet.gr/~athsam/remove_sound_from_stereo_signal.htm