Spectrogram Puzzle tutorial

In this article, we’re going to go over how to create a Spectrogram puzzle, viewable in audio spectrograms. All while using free tools!

What is a spectrogram?

Spectrograms are graphical representations of audio signals that depict the intensity of different frequencies as colors or shades of gray. They have been used by audio engineers and scientists for decades as a tool for analyzing and manipulating sound. In the early 2000s, some creative individuals discovered that messages or images could be hidden in the spectrograms of audio files.

For example, if you were to listen to a piece of music, the spectrogram of that audio file would show you the intensity of the different frequencies at each point in time. However, if you were to modify the audio file in a specific way and then view it as a spectrogram, you might notice that certain frequencies appear at higher or lower intensities than they should based on the original audio. These anomalies could be used to hide a message or image within the spectrogram.

This technique was quickly embraced by the creators of alternate reality games (ARGs), who used it to include cryptic clues or puzzles in audio recordings distributed as part of their games. These hidden messages, known as spectrogram ciphers, could only be revealed by viewing the audio file as a spectrogram and analyzing the patterns of intensity. Solving spectrogram ciphers became a popular activity among ARG players, who often used them to unlock new content or progress in the game.

What You’ll Need:

Audacity, or any other spectrogram visualization tool (https://www.audacityteam.org/download/)
Coagula Light (https://www.abc.se/~re/Coagula/Coagula.html)

Coagula Light:

So, I quickly popped photoshop open to generate an image (above) that would be “brand related” to the site. This part is totally not necessary. You want to grab whatever image (keep it fairly simple. Text works best), and open up Coagula.

After you have it open, hit File>Open Image> and then select your image.

(Note: Horizontally long, vertically short images work best to avoid stretching.)

Now that you have the image open, check the “Show image brighter than real” icon, and then hit “F6.” This will render the image, without blue. You’ll likely hear some strange alien sounding audio that will make absolutely no sense. This is exactly what we’re looking for.

Once you’ve rendered the sound without blue. Go ahead and hit File>Save Sound As… and pick a location/name for it. Once you’re done with that, swap over to audacity, and bring the new sound in. Now we’re going to verify the image has been embedded into the Audio.

Audacity:

Now that it’s in Audacity, go into the track setting, and enable the spectrogram view on the audio file as pictured below:

This is what the new image should look like, with the exception of it being your image, instead of mine.

If it doesn’t show up exactly as intended, stretched or shifted… Go to Tools>Render Options in Coagula, and up the low and high pitch, as shift the time around. These are your Vertical/Horizontal transform tools, respectively.

Tune it until you’re satisfied, and voila! You have created your new Spectrogram secret message!

From here, you can layer it in with other audio, release it standalone, play it in the background of a voicemail… the possibilities are endless!