Airplay Mirroring or HDMI cable - not sending audio
I have a Macbook Pro Retina Display, and I'm trying to connect it to a TV set.
I tried with a direct HDMI cable and via Airplay Mirroring to the Apple TV, and in both ways the audio data is not sent to the TV but I hear it from the Macbook's speakers.
Which are the proper settings to fix it?
Thank you
MacBook Pro (15-inch Late 2008), OS X Mountain Lion, 2.4 GHz, 4 GB RAM