Example: packing microphone signals

To pack signals from two microphones into left and right channels of a single stream:

In VAC Control Panel, choose a Virtual Cable and configure its format range to accept a stereo (two-channel) stream. Make sure that the Enable channel mixing checkbox is cleared and "Ch mix" is "off" (channel mixing is disabled). This enables the scatter/gather feature. Leave Control Panel open to watch cable signals.

VAC Control Panel with channel mixing disabled

Set default format for the recording endpoint to "stereo", with desired sampling rate and bitness.

Line 1 with default recording format 48000/16/2

Run two instances of Kernel Streaming version of Audio Repeater. In each of them, choose the appropriate microphone pin as "Wave In", and leave "Wave Out" to be "None". Set input/recording channel configuration to "Mono".
Try to start each repeater to make sure that both microphone pins support selected sampling rate and bitness. If the repeater shown an error message related to unsupported format, correct sampling rate and/or bitness, and try again. If the microphone pin does not support mono (single-channel) formats, it cannot be used for such task.
If both repeaters are successfully started, speak into each microphone to make sure that the appropriate signal indicator moves, and stop them.
In both repeaters, choose the same Virtual Cable as "Wave Out", and set output channel configuration to "Custom". In first repeater, check the "FL" output box; in the second, check the "FR" box. Only a single channel should be checked in each repeater. Set number of channels to 1 in both repeaters.

Start recording/processing application (for example, Audacity) and choose the appropriate "Line N" recording endpoint (if possible, use WASAPI interface). Configure the application to record a stereo stream.
Start recording and make sure that VAC Control Panel shows that current audio format is stereo.
Start both repeaters, speak into microphones and check that the appropriate signal level indicators in VAC Control Panel are moving. If the recording/processing application has such indicators, they should move too.

Instead of microphones, you can use any other audio recording devices, or even signals produced by other applications, passing them via additional Virtual Cables. You can pack up to 8 signals by default, and up to 32 maximum. Just configure the appropriate formats for Virtual Cable, and run a separate Audio Repeater instance for each signal.