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You're a KGB agent currently in Russia who had experience with weird email.

Now, you had received an envelope from the front of your door with the following:

  1. A letter saying "Fly to this airport."
  2. A tape

You sighed. Passport, check. Visa? You can steal your neighbour's and forge it. If you need to use any electronics, you realized that you can buy a transformer at a home depot.

Technical detail:

The first ever audio steganography in this site requires heavy programming skill. The only thing you need is a simple audio player, like the one I provided.

First hint:

It has been identified that the tones consists of sine wave, square wave & sawtooth wave.

Second hint:

The letter said "Go to this airport," so intuitively the answer will ask the KGB agent to go to an airport, not a city(ie. Glasglow =D)

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  • $\begingroup$ so we have to decrypt those 3 sounds on the tape? that sound has encrypted name of place where we are supposed to fly to? $\endgroup$
    – Wasiq Shahrukh
    Commented Jun 11, 2016 at 16:21
  • $\begingroup$ The technical details says its all. All you need is an audio player. I can't tell more for the time being, I want to gauge the reaction because this is something new for me. $\endgroup$
    – Realdeo
    Commented Jun 11, 2016 at 16:26
  • $\begingroup$ Yes, the message is in the sound. To clarify. $\endgroup$
    – Realdeo
    Commented Jun 11, 2016 at 16:29
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    $\begingroup$ Is downloading the file necessary? $\endgroup$
    – cyberbit
    Commented Jun 11, 2016 at 19:51
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    $\begingroup$ @cyberbit In theory, yes. In reality, unless you have massive creativity and massive memory, it may help to listen it more than once. $\endgroup$
    – Realdeo
    Commented Jun 13, 2016 at 3:46

5 Answers 5

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Partial observations:

There are 3 parts of sound. The first is long 3.161 seconds and contains sine wave with frequency 440 Hz which is A4. The second part is 3.129 seconds and has 18 frequencies starting from 440 Hz and distributed equally with intervals of 880 Hz. The third part is 2.852 seconds and contains 35 frequencies starting from 440 Hz and equal intervals of 440 Hz. But I don't think all those could be obtained using just a player though.

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  • $\begingroup$ what about the time domain? a sine, a triangle, a square? $\endgroup$
    – Jasen
    Commented Jun 12, 2016 at 4:31
  • $\begingroup$ @Jasen For 18+ frequencies it is not obvious. Fourier analysis represent any wave as sum of sine waves. For precise answer one have to guess and try to synthesize a similar sound and compare, but the problem is that parameters are too many - shape, amplitude and phase for any of the frequencies, and frequency analysis can give only rough idea about the last two, and none for the first :) $\endgroup$
    – kamenf
    Commented Jun 12, 2016 at 9:49
  • $\begingroup$ Yea, I'm not sure the number of frequencies are the right track. OP said the solution can be found using only the online player, and (in theory) a single play through. $\endgroup$
    – cyberbit
    Commented Jun 13, 2016 at 13:41
  • $\begingroup$ Plus, as @niemiro pointed out, the three waves are all the same musical note, A4. Any additional frequencies might be interference/resonance patterns, as they are regular and at factors of 440 Hz (A4). $\endgroup$
    – cyberbit
    Commented Jun 15, 2016 at 13:44
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Here it goes. Sorry if I overdone it with roleplay.

You had previous experiences with steganography puzzles but you don't usually get challenged by an audio puzzle. You say "Bring it on" and start working on it.

You realize that the person who sent you this tape wouldn't go as far to involve a programming puzzle in it. Because they would probably know you don't have that much of programming skills.

You play the tape. You can tell from the first play that there are 3 different parts. Different parts of sound would probably correspond to 3 letters of an IATA airport code.

After playing the sound a couple more times, you identify the parts as sine wave, square wave and sawtooth wave in respective order. You think you have every hint you can get from the sound. Rest is up to your imagination.

A sine wave looks like letter S, a square wave looks like letter U, a sawtooth wave looks like letter Z. You look up the SUN code and board a plane to the Friedman Memorial Airport in Idaho, US.

As you watch clouds from the plane, a fear surrounds you. What if you were wrong? Was there something hidden deeper in the sound? Would the author of the letter choose such a remote place? Guess it was too late to think over it. You will see when you arrive at the airport anyways.

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  • $\begingroup$ You are the most closest one. You are on the right track. $\endgroup$
    – Realdeo
    Commented Jun 20, 2016 at 8:23
  • $\begingroup$ Remember the clue that he needs visa from Russia and he needs transformers to use electronic application. $\endgroup$
    – Realdeo
    Commented Jun 20, 2016 at 8:24
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    $\begingroup$ I think, that square is more like n, so it could be Grosse Ile Municipal Airport in US. $\endgroup$
    – Artholl
    Commented Jun 20, 2016 at 12:59
  • $\begingroup$ @Artholl That didn't occur to me. Thanks. But then it would be SNZ which is Santa Cruz Airport in Brazil. Brazil has different power outlet from Russia. But no visa is required to visit Brazil according to Wiki. I am going with another answer. $\endgroup$
    – Gokhan Kurt
    Commented Jun 20, 2016 at 13:04
  • $\begingroup$ @GökhanKurt My bad. I wrote ONZ, not SNZ :-). $\endgroup$
    – Artholl
    Commented Jun 20, 2016 at 13:06
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There are three waveforms represented in this clip: Sine Wave, Square Wave, and Sawtooth Wave.

Taking the...

first letter of each wave gives us SSS

Therefore we should fly to...

Siassi Airport (SSS) in Siassi, Papaua New Guinea

Old Answer:
The sound is bagpipes. Fly to GLA (Glasgow, Scotland).

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  • $\begingroup$ :) this seems as good as any answer $\endgroup$
    – Jasen
    Commented Jun 12, 2016 at 4:32
  • $\begingroup$ Thank you for the answer but no. $\endgroup$
    – Realdeo
    Commented Jun 12, 2016 at 6:16
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Location -

Anaa Airport, French Polynesia

Encoded message -

The message encoded in the audio file is "AAA", the IATA airport code for Anaa Airport.

Explanation -

It's a musical challenge! Despite the sine wave, square wave & sawtooth wave parts of the message all sounding slightly different, they are in fact all the A4 musical note (the first A above middle C/the 440Hz note musicians use to tune their instruments [https://en.wikipedia.org/wiki/A440_(pitch_standard)]). Therefore the message is A4 A4 A4 or just "AAA". If you're able to hear tone then you can compare 440Hz notes (A4) here: http://onlinetonegenerator.com/. If you're a practiced musician you're likely to be able to recognise A4 without assistance from such tools, i.e. just with the simple online music player given.

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  • $\begingroup$ Good answer! You're implying that the hint about the types of waves was a red herring? $\endgroup$
    – LeppyR64
    Commented Jun 15, 2016 at 12:49
  • $\begingroup$ @LeppyR64 - in theory yes, but in practice no. The wave forms do not change the notes so in theory you do not need to know this information. However, for a non-practiced musician, hearing that the sawtooth note and square wave note are in fact the very same A4 is tricky. Note how none of the above answers said "They're all the same note!"? The hint isn't strictly necessary, but it would be a very big help for a non-practiced musician trying to compare the sound file given to the sounds from the online tone generator I linked. So not a red herring, but only needed by some people :) $\endgroup$
    – niemiro
    Commented Jun 15, 2016 at 12:55
  • $\begingroup$ When looking at the particular website onlinetonegenerator.com I think it becomes clear why the hint was given as it was (and probably also why A4 was chosen, again for the non-practiced musicians). $\endgroup$
    – niemiro
    Commented Jun 15, 2016 at 12:58
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The correct answer is the following

The Sine Wave do look like an inverted S.
It is correct that Square waves look like the letter U, but a single square wave look like lowercase A Sawtooth waves looks like a N

Therefore

SAN: San Diego International Airport

In addition to that

You need visa from Russian to U.S. Russian voltage is 240 V while U.S. is 120 V--hence the transformer clue.

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