This could be because:
- The speakers of your computer are not plugged in, turned off or their volume is low
- Your microphone is plugged into an audio channel that does not correspond to the video input channel
- The Windows volume control is muted or turned low
- When you work with Windows 7, you have selected Line-in for your audio device instead of Microphone.
When you plug in a microphone, Windows asks you if it is Line-In or Mic. You can set the default recording device from the Windows Control Pannel select Sound and then go to the Recording tab.
- You do not have an audio source connected.
The Observer, Media Recorder