I talk a lot about sound quality in video production. If the audio is poor, then your audience gets bored, distracted or irritated and you can lose them.
I made this video (rather quickly) for a presentation I gave, to demonstrate the difference between using the internal camera microphone and an external mic that it plugged into the camera.
The camera is a Sony HVR Z5E and the microphone is a Sennheiser EW 100_ENG G3. You don't need to use a microphone as expensive as this, or a wireless mic, it's just what I normally use.

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