Challenge

We received an audio clip of a duck repeatedly quacking. At first glance, it sounded random, but my instincs were telling me something different.

Step 1 --- Generating the Spectrogram

Using sox, I converted the audio into a spectrogram (you can also use audacity or similar tools):

sox duck_sound.wav -n spectrogram -o duck_spectro.png

The resulting image revealed evenly spaced bursts corresponding to each quack. However, unlike typical spectrogram-text challenges, no visible characters appeared. The pattern was purely rhythmic, like morse code!

Step 2 --- Identifying the Pattern

Each quack had a consistent spacing and duration, with short and long bursts separated by pauses.

By analyzing the spectrogram columns:

• Short bursts corresponded to dots .
• Long bursts corresponded to dashes -
• Medium gaps separated letters
• Large gaps separated words

After mapping those timing intervals into bits, the decoded Morse output was:

...- .---- -   -.. ..- -.-. -.-   ... ----- ...   ... ----- ...

Step 3 --- Decoding Morse

Translating that Morse sequence gives:

v1t duck s0s s0s

Flag

Combining the decoded text into the standard flag format:

v1t{DUCK_S0S_S0S}

Notes

It's important to note that the author used 0's instead of O's, possibly just to confuse solvers or just to partly implement 1337 (leet speech) [external]. Granted he didnt turn other characters like S's into 5's, which is very common in leet speech.