So we recently received a notice that we’d been selected by Nielsen to participate in media consumption monitoring. Originally we thought cool, weigh in on shows we watch, then we looked at their program now. Now more monitoring you viewing, instead you were a device much an oversized pedometer that listens. In measures what you are watching or listening to by picking up the audible signal in all monitored TV and radio broadcast with signals encoded every 2.5 seconds roughly. It’s there under the dialog or other sound on the broadcast.
Just thought it was interesting there is now a timestamp digital pulse every 2-3 seconds on almost every broadcast to identify show and time in show. Makes you start to wonder what else is getting buried in the signal
Interesting (from a technical point of view). I once had to look at how to encode timestamping in transmitted audio for sync purposes (long story). The method that was least perceptible was phase shifting frequencies (or select frequencies) at a period below 60Hz. Anything faster and it may be perceived as a sound. The other problem is that the transmission of most ‘voice’ speakers is above 200Hz and below 3kHz. While some people may have high quality audio systems attached to their TVs, not everyone does. I suspect that the timestamp pulse is more like every minute or so, or even less to avoid collision between transmissions. It could be that a encoding phase transitions occur every 2-3 seconds – kind of a 1/2 baud transmission.
You are kind of doing audio-steganography. If the bandwidth of the data being transferred breaks into the region of human hearing – it will be perceived.
Now I am tempted to digitize a bunch of network audio – and find out if I see phase shifting… I wonder if I can see the phase shifting in digitally encoded audio from video data – some video encoding uses something similar to mp3 encoding for audio.
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