Synthesizing a 5.1 Home Theater using Upmixing

If you have 2 channel stereo PCM input, you can synthesize a 5.1 channel home theater using upmixing techniques. Here we create the center channel by positively mixing the left and right channels into the center channel. You also can add gain and bandpass filters to emphasize the voice. The left and right surround channels are created by subtracting and attenuating the left and right channels. Note in the diagram how the mixing uses inversion for subtraction.