TV audio overdubbing proof

If you analyze the transmitted audio spectrum of TV-stations, you will find that a 15625 Hz sinus tone sometimes appears very strong in the spectrum, but only in some passages.

The explanation: a TV screen was near the microphone when the commenting was recorded. Any TV screen produces such a mechanical sound, which is very high and for some people not audible anymore. A vibration is being produced any time a new line appears (25 times in a second multiplied by 625 lines = 15625 lines in a second if it's European standard). Knowing this, many sorts of overdubbing can be revealed. This can be often monitored during commercials, too. There is also a weaker 16385 Hz tone that co-appears with the 15625. I haven't found out the origin of that one yet. Still it remains a little bit unpredictable when this tone can be noticed. -> experience