How are you planning to receive the audio? Naturally, you'll want a way to feed in pure audio like from an mp3 player or perhaps a phonograph, but any plans to build in a microphone? That way you could have it displaying ambient sound if there was no direct line-in audio source connected. Plus if you had music playing it would still pick that up, albeit not as good of quality as a direct input. The major downside I see with a microphone is the audio will only be as good as the microphone you choose, and they can get pretty expensive when you start to consider things like consistent frequency response and having a -3dB bandwidth in the full audible range.