Plug your microphone into the microphone socket on your OtsAV main ON-AIR output soundcard.
Go to the Options -> Live Input -> Show Live Input control box... menu.
Check that the Air option is selected.
Click on the Spawn Mixer Record Properties... button and select the microphone device. Adjust the microphone slider to approximately 3/4 (Depending on your system and the microphone being used you may wish to select Advanced and select the 20db mic boost option).
Select a Headroom and Dynamic Range option. You are best to select the 12dB headroom, good dynamic range to begin with.
Select Method A or B depending upon your latency requirements. You may want to try and reduce the Live Input latency by using the Method B configuration. You will need to experiment with the calibration values to find out what best suits your system. We have found that the optimum value for most soundcards is 3.
Select the On option at the top of the Live Input dialog box. You should hear your microphone through your ON-Air speakers.
You will now need to adjust the Live Input level slider to obtain the strongest signal, but with No clipping.
Live Input feature
How to set up an external device through Live Input
How to use Live Input