Which keyboard are you using?
I think the Motif has an input for a microphone.
How are you pluggin the Motif into the Mac?
Need more info to be any help

Well its a huge MOTIF keybooard/piano replacement. Im not sure what model it is..

I put a 1/4" to 1/8" converter into the mono out and then plugged a double ended 1/8" cord into it and into my input in the mac.. I got no sound. So i came home and learned that Under system preferences I had onboard microphone channel active and not the "line in" channel active. So i tried to plug in my headset that i use for PC gaming into the mac and I got nothing.

Can you plug an instrument straight into a macbook without any audio interfaces and it record in garage band?

if your mac has a line input thats what you should use for the keyboard not the mic input.

Theres only one port for anything to be considered a "line-in" on the mac. The other little hole is for speakers or headphones. Theres 2 USB and a firewire 800. What picked up ANY sound was the external mic (crappy one used with webcam) and not the line in that had all the cords running from the MOTIF to the macbook.

Do i need an audio interface or is this possible without any peripheral hardware?

Mike0811:
Maybe this will help you

http://guides.macrumors.com/Recording_on_a_Mac

This is a routing issue. You need to set the active input to line in and make sure it stays at that.

You can probably plug a mic into the input, and get a tiny little bit of signal.
You know when you tune a radio out and all you hear is static? You get 90% that, 10% signal.

Mics need preamps. They're designed to reject interference and bring the signal level up up up into usable levels that other gear is designed to work with.

So in short, yes you can go directly in with a mic unless you want a usable signal.

You need to set the core audio to use the line-in as the recording source either from the garage band prefrences or from the system prefrences-audio setting.