The data is encoded in subtle shifts in the frequency. This is a type of modulation. Look up https://en.wikipedia.org/wiki/Signal_modulation https://en.wikipedi

The data is encoded in subtle shifts in the frequency. This is a type of modulation. Look up https://en.wikipedia.org/wiki/Signal_modulation https://en.wikipedia.org/wiki/Signal_modulation and https://en.wikipedia.org/wiki/Frequency-shift_keying https://en.wikipedia.org/wiki/Frequency-shift_keying