From SoMud, go to "Utility Tools" menu, choose "Capture Audio/Video" to invoke Audio/Video Recorder.
From Audio/Video Recorder, start a new recording task. For "Capture Type", select "Desktop/Microphone Sound". For "Audio Input", if you want to record both desktop audio (sound from your computer) and microphone audio at the same time, you can choose "Wave Out Mix" or something similar (for different audio devices, this name may be a bit different); if you only want to record microphone audio, then choose "Microphone" as audio input line. Then press "OK" button to start recording.