Read this section only if the sound card is only capable of one-channel simultaneous play and record. This is a very special case.
If you have such a card you cannot perform 2-channel measurements. The card will support 1-channel measurements without using a synchronization loop. But if the card has both a microphone input and a line input and if it supports the WinMLS mixer, WinMLS also support 1-channel measurements using synchronization loop for such cards. To do this, you must choose different inputs for the Input Line and the Loop-back Input Line as described in the chapters above. Then make the synchronization loop by connecting a cable from the sound card output to the input you choose as Loop-back Input Line. Note that you need to split your output cable from the sound card. One part is for the synchronization loop that we just showed how to connect. The other part is for the output signal.