A puzzle that I would be most grateful for any help with!

Special Interest Groups Audio Processing
1

I am trying to solve a puzzle that involves a WAV file that has information hidden within it.

This is the file:https://www.dropbox.com/s/yc4wxspw2b35o49/puzzle.wav?dl=0 (the file is free of anything untoward as far as I can tell!)

The clue that is given is A.M. which I have taken to mean amplitude modulation. You are also given the numbers 20000 and 96000 which I have taken to be frequency.

Using this forum I used the following script: (mult (sum 0.5 (scale 0.5 (aref s 0)))(aref s 1))

This reveals hidden audio at the start and end of the file. However, whatever is being said in between is being obfuscated by the left track (a reversed backtracked rhubarb track).

I would be super grateful for any ideas people may have that will allow me to hear the entire hidden signal, if there is indeed any more to hear!

Thank you in anticipation, and my apologies if as a first time poster I have made any forum faux pas with this post.

2

Well the sample rate is 96000 Hz, and a plot spectrum shows a strong peak at 20kHz with symmetric sidebands so it’s a fair guess that there is something modulating a 20 kHz carrier there. I’ll leave the task of writing a suitable demodulator in nyquist to you.

3

Solved: thank you.