If I remember correctly, audio was transmitted on a subcarrier some 6 or so MHz higher?
Edit: Later in the article it is actually stated: "A normal SECAM signal uses FM on a 6Mhz carrier"
That's why when inverted it was sounding like crickets speaking.
You could unscramble the sound just by multiplying it with the right sine wave at the right frequency.
I remember prototyping that with a modular synthesizer :-)
If I remember correctly, audio was transmitted on a subcarrier some 6 or so MHz higher?
Edit: Later in the article it is actually stated: "A normal SECAM signal uses FM on a 6Mhz carrier"