The Problem With 13″ MacBook Pros

You need an audio interface, not just a MIDI interface. An audio interface is essentially an outboard audio card for you Macbook. The Macbook Pro 13" is a consumer product, its not designed to be a pro audio recording device. The little soundcard in there does not have great bandwidth, and trying to monitor both input and output signals would likely pose latency issues.

You need something like the M-Audio Fast Track: http://www.guitarcenter.com/M-Audio-Fast-Track-USB-Computer-...

It's the same on the new Lenovos. I have a T510 and it has only one jack for mic input and headphones (probably using a 4-contact jack). I cannot use it for Skype until I find a new pair of headphones with mike that has that jack. In the meantime I have to use a Bluetooth handsfree.

baitsplanation: his 2009 mbp has a combined input/output jack, which is a problem in garage band. usb is considered to be an option.