Audio Line-In Not Audible

Hi, I just purchased a new MacBook recently and have tried using it with Serato Scratch Live. The program runs fine, but I am having a problem with the audio line in. While I can plug my mixer's output into another computer and hear the audio, when I plug it into my MacBook I cannot hear anything. The strange thing is that when I go to sound in System Preferences, the audio input is detected in the 'input level' graph. I have an RCA to 1/8" adapter coming out of my mixer and plugged into the small jack next to the headphone out.

If anyone has any info on this it would be greatly appeciated.

The input is probably set to the mic. Go to sound in the preferences menu.

The input level graph might be just showing you what is coming in through the built in mic of your Mac. Be sure to select the line-in from the list in the input tab.

Nah, it was set to line-in in audio in system preferences. I just had to open a program like garage band and 'create an instrument' in order to monitor the line in on my macbook.
I was a bit confused because windows will play back any sound passed through the line in port without opening any programs.