2-channel loop-back for sound cards with two inputs (e.g. line and microphone input)

If your sound card has two input lines, e.g. Line and Microphone input, no external device is needed to sum the signals needed. The signals can be summed using the two physical inputs of the sound card. Some sound cards also have an internal loop-back that can be used. These two options are explained below.

 

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Loop-back using two physical sound card inputs

Loop-back using sound card internal loop-back