If you are using such a display you will have to make sure that the monitor's settings are correct. If you are using an AppleVision display, look at the buttons on the audio console at the bottom front. There is a microphone icon, and beneath it a small indicator light. If that light is not red, the mic is turned off. Press the button just below to turn it on.
Microphone technique Try to work in a quiet location.
Any background noise will be recorded and will sound surprisingly loud. Speak with you lips about 6 inches from the microphone. If you get too close, the recording will be muffled. Enunciate clearly and maintain an even attack and volume. Start speaking just after you begin recording and stop recording as soon as you have finished speaking.