Tags: forensics 

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# SOS

We're given an audio file. If you listen closely, you can hear that there's some sort of beeping in the background. It can be processed through Audacity (Effect > Change Pitch). I applied a -95% change frequency.

We now have an audio file resembling morse code. There's still some background noise. We can again filter out unwanted noise using Audacity (Effect > Plug-in 15 to 17 > High Pass Filter). I applied a high pass filter of 1000 Hz with a roll-off of 48 dB per octave.

Now what remains resembles Morse Code without the background noise. We can simply listen to decipher.

![](https://raw.githubusercontent.com/shawnduong/ctf-writeups/master/2019-TJ/images/sos.png)