To apply effects to the loopback audio on VT-4, please configure the settings as follows:
When applying effects to computer playback sound and recording it with DAW software, set the output of the playback track to 'VT-4 TO MIC IN' and the input of the recording track to 'VT-4 MIX.' Please note that the audio from the microphone connected to the VT-4 unit is also sent to the computer during this setup.
If you want to record only the loopback audio, either disconnect the microphone from the VT-4 unit or turn the [MIC SENS] knob all the way to the left.
* On Mac or certain software, 'VT-4 TO MIC IN' may be labeled as '3-4,' and 'VT-4 MIX' may be labeled as '1-2.' For more details, see to 'Using the VT-4 As a USB Audio Interface.' in the VT-4 Owner's Manual.