Connect a loop-back to be used as reference

A loop-back is typically a cable connected from the output to the input of the sound card as shown in the figure below. The output signal is always played back in the left channel and the loop-back output signal is played back in the right channel (for >2 channel measurement other rules apply). Connect the cables as shown in the figure below, with a cable between right channel output and right channel input.

Figure 5 Schematic diagram for one-channel measurement using loop-back

You might need to purchase extra cables for the sound card to be able to connect the loop-back.

Note: The microphone input on a standard sound card is mono. If you try to connect to such an input, no right input channel exists. If this is the case and your sound card has a line input, you may connect the loop-back input cable to the right channel input of the line input.

If your sound card only has a microphone input, which is the case for some built-in laptop sound cards, you cannot do what is described in this section. However, you can still correct for your measurement system as explained in the Measurement 5 section below.