Turning off built in mic

I'm not sure if this is the answer you're looking for, but if you are picking up noises from your computer mic (or any mic for that matter) and you want to turn them off, you can click on the "Input Monitoring" button on the individual tracks to turn the monitor on or off. It is the orange button to the right of the mute and solo buttons in the track controls.

Same problem here. Trying to record with a keyboard. I can hear the ambient room sounds, so those sounds are not obviously coming throuhg the keyboard. On my Macbook air, there is no option through System pref to select 'Line-in' - there is only one line in that window - 'built-in mic'. And yes, I did select the 'real instrument' through GB audio pref......

Any ideas?

I was having the same issue when I wanted to listen to and edit projects after I'd unplugged my digital interface, but didn't want to hear myself typing/breathing as I did so!

What worked for me was to turn ambient noise reduction on and max out its sensitivity.

Here's what to do:

In Garageband:

1) Garageband menu → Preferences

2) Choose Audio/MIDI

3) In "Input Device" dropdown, choose "Built-In Microphone"

(If it won't let you do this, then try it again after doing the below and it should work; worked for me.)

In System Preferences

1) Go into Apple menu → System Preferences

2) Choose Sound (Second row, furthest to the right)

3) Choose "Input" heading

4) Select "Internal Microphone_Built-in" as the device for sound input

5) Make sure box is checked next to "use ambient noise reduction"

6) Drag the "Input volume" slider all the way to the left (This makes the internal mic so sensitive to external noise that it basically just stays shut off/silent while you work on your project).

This may not work if the issue you're having has to do with multiple conflicting inputs, but it resolved my issue perfectly. I hope this helps

There is no 'Line In' option on mine!