I'm new in using teensy. I want to do a project regarding audio EQ using teensy 3.1 with audio shield for teensy 3. However, when I'm trying out with the codes given in the arduino examples, there's no audio output from my headphone when I pluck in my headphone to the audio jack.

My question is, how do I write out the code in the program in order for my audio to be output from the headphone?