2-channel loop-back for sound cards with one input only

If your sound card only has one input line, e.g. Line input, a device has to be used for summing the signals, see the figure below. An audio mixer or a passive device (consisting of 3 resistors) can be used, you may also contact us for purchasing such a device.

Figure 6 Schematics for two-channel measurement using synchronization loop-back for one single input.