I think I hear an additional bit of trickery that the article didn't mention: the morse signal keeps oscillating between the left and right stereo channels, whi

I think I hear an additional bit of trickery that the article didn't mention: the morse signal keeps oscillating between the left and right stereo channels, which on headphones or a nice speaker system make it sound more like artsy synth and less like a coded message. If the illustration in the article is accurate, the hostages are probably listening on a monophonic radio or one with limited stereo separation, which would make the code easier to pick out and understand.