[jdietrich]

You can't count on a TV being able to reproduce sounds below about 100Hz or above about 16kHz. The position of the speakers on the back of the TV means you're likely to get a lot of weird phase effects and many TVs have quite heavy audio DSP to compensate for the inadequacy of their speakers. Any hidden signals will need to be in-band and low bit rate with a high level of redundancy.

[tinus_hn]

You can even less expect all the compression in the system that’s designed to leave out everything people can’t hear, to leave in this signal people can’t hear.

[derefr]

So, basically, steganography.