EchoJack is an audio utility that lets you
play through audio from any input device to any output device. EchoJack can be used to do the following:
1. Monitor the audio recording using headphones.
2. Create a makeshift Public Announcement (PA) system. Simply hook up your mac’s line-out to an amplifier, turn on EchoJack, and speak into your mac’s microphone. Your sound will play through to the amplifier.
3. Add voice comment during media playback. Simply turn on EchoJack when playing audio/video media, and speak into your mac’s microphone. Your voice will be mixed into the media output sound.