How can I set output to internal speakers after I've set the 3.5mm jack as input on 13" MacBook Pro? I have a 13" MacBook pro, which has only one 3.5mm jack. I've set it as Sound Input in the System Preferences -> Sound dialog



This way I can record directly from my piano audio output. The problem is, I'm not able to hear anything anymore. The piano has only one 3.5mm jack, and if I put anything in there, it's speakers get turned off.

I'd like to make my MacBook replay the sound it's getting on the sound input in it's built in speakers, so that I can hear what I'm actually playing.

When I try to play any sound directly (like in iTunes), it uses the speakers just fine. But it doesn't play the sound that is being recorded from the 3.5mm input.

Basically this would be the equivalent of hearing yourself speak when talking on Skype.
Have a look at the free
LineIn
Inside The Lines
LineIn is a simple application for OS X to enable the soft playthru of audio from input devices. In simpler terms, you can use LineIn to play sound coming in through a microphone or any other device plugged in to your Sound In port, just as was once available with OS 9's &quot;Play input through output device&quot; option.