surround sound circuit

The surround sound processing circuit introduced in this article uses a 2-2-4 analog surround sound system. The circuit is shown in Figure 10-18.
The following briefly describes the working principle as follows:
    The signal from the left and right channel equalizer is from pLPC1891⑧ , ⑨ pin input, after internal processing,
three signals are output from ②, ⑧, ⑨ pins respectively, namely left channel composite output, right channel composite output and surround sound output. In addition, the @ and ⑥ pins are status
control interfaces. Three different output effects can be obtained by inputting different voltages to the two pins.
    When sl is in the "analog" position, the @ and @ pins are connected to +5 V at the same time for the "analog stereo" effect, that is, the input channel signal
will produce an analog stereo effect.