Audio Port/Guitar input

Hi Apple Community,

I recently (3 weeks back) got an iMac 27" (late) 2012 model which, while a great jump up from my earlier 2010 model, is giving me a hard time as far as recording my guitar in Garageband is concerned.

The earlier iMac had separate input & output ports at the back but this one has only one audio input/output port at the back.

I used to use iRig for guitar input interface & it worked beautifully on my earlier mac. With this one there seem to be issues.

First of all when I plug in iRig, in my sound input field I only get the 'External microphone'/ type: microphone port' option. There is no other option for a line in etc.

I searched the forum and found a post that mentioned the 'Use Audio Port for' option for macs that have only one audio port.

The problem is that option is not available on my system. I don't know if it is a limitation or there's a compatibility issue with iRig, but that option is just not available on my system.

Furthermore, as iRig has a built in headphone out I also don't get an option to use the system speaker for sound out.

There is no way for me to test if this is a limitation of the new iMac or a compatibility issue with the iRig interface as I don't have any other interface gadgets available to me.

If I use the external headphone option in sound input panel I get incredible amounts of feedback and can't really use it at all.

Any help that anyone can provide in this regards would be incredibly helpful since my garageband is rendered useless as of now.

Thanks,

flyashy