Audio input through external microphone not 'heard' by computer
I can record audio with any app through the builtin mic. And I know the system 'hears' sound through the builtin mic when I go to SystemPreferences->Sound->Input.
I have an external microphone that I want to record through. I went to SystemPreferences->Sound->Input and chose 'Line In' and plugged in the microphone's lead into the 'in' jack. However the SystemPreferences->Sound->Input Input Level sensor/detector is dead -- it shows no audio input. Nor does iMovie pick up any audio input when the mic is plugged in.
I know the input jack works by plugging in the output pin from a cassette-player, choosing 'Line In', and playing a cassette. The Input Level sensor/detector comes on and the sound is available to apps.
I know the external microphone works by plugging it into the cassette-player and recording from it and tapping and rubbing on its pick-up. The sounds are captured on cassette tape.
So why is audio input through external microphone not 'heard' by the computer? Is there some trick to making it work?
Mac OS X (10.4.11)