Yes, but with several caveats. You could to put it in a frequency band unused by the surround audio, but masked by the center - but this would show up very distinctly on spectrograms or phase analysis. Likewise, one could modulate the panning of a particular frequency band across the left and right, but that would also be quite noticeable on visual analysis.
You could do wideband modulation that would be much harder to detect, but only if your music is repetitive...such that you subtract, say, the instrumental content of the first verse from that of the second to reveal your hidden message. That's not so difficult, given the ubiquity of loop-based and electronic music nowadays.
One other issue with all these schemes is that the more well-hidden your steganographic message is, the more likely it is to be corrupted or destroyed by conversion to lossy data formats such as mp3. If you absolutely had to hide a message in musical form, I think it would be better to do in the manner of the purloined letter, ie haiding it in plain site. Encode it into the rhythm of the cymbals, or the sequence of pitch differentials in the primary melody or some other foregrounded musical element. You can use binary strings or a sequence of rational integers as musical elements very easily, and said sequences can be pre-encrypted. Sure, the signal is even more visible in that context, but who's to say that it's covert or merely artistic?
You could do wideband modulation that would be much harder to detect, but only if your music is repetitive...such that you subtract, say, the instrumental content of the first verse from that of the second to reveal your hidden message. That's not so difficult, given the ubiquity of loop-based and electronic music nowadays.
One other issue with all these schemes is that the more well-hidden your steganographic message is, the more likely it is to be corrupted or destroyed by conversion to lossy data formats such as mp3. If you absolutely had to hide a message in musical form, I think it would be better to do in the manner of the purloined letter, ie haiding it in plain site. Encode it into the rhythm of the cymbals, or the sequence of pitch differentials in the primary melody or some other foregrounded musical element. You can use binary strings or a sequence of rational integers as musical elements very easily, and said sequences can be pre-encrypted. Sure, the signal is even more visible in that context, but who's to say that it's covert or merely artistic?