We got a pretty robust system working; the watermark in audio clips was able to withstand addition of noise and mp3 compression. I'm sure this has been taken much further to be resistant to many more kinds of attacks. Just google "digital watermarking of audio signals".
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I actually used this exact same idea for my master's project. It is based on this paper: http://www.ragomusic.com/publications/ragoAES1999. pdf
We got a pretty robust system working; the watermark in audio clips was able to withstand addition of noise and mp3 compression. I'm sure this has been taken much further to be resistant to many more kinds of attacks. Just google "digital watermarking of audio signals".