Moanin

task

Any true jazzer knows that you’re always supposed to listen in mono. I got this track from my dad’s old records. It’s a bit scratched in some spots. Could you help me convert it to mono, and maybe even remove the scratching?

(the flag is 1 word, wrap it with flag{})

Author: Stephen

Tags: steg

writeup

Ok so the track we get is called moanin.wav.

Here is the file:

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file moanin.wav 

moanin.wav: RIFF (little-endian) data, WAVE audio, Microsoft PCM, 16 bit, stereo 44100 Hz

The file utility tells us, that it is a normal 16 bit wave file.

Also running exiftool against it does not reveal much

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exiftool moanin.wav 

ExifTool Version Number         : 12.44
File Name                       : moanin.wav
Directory                       : .
File Size                       : 103 MB
File Modification Date/Time     : 2022:11:17 22:35:46+01:00
File Access Date/Time           : 2022:11:17 22:42:11+01:00
File Inode Change Date/Time     : 2022:11:17 22:42:05+01:00
File Permissions                : -rw-r--r--
File Type                       : WAV
File Type Extension             : wav
MIME Type                       : audio/x-wav
Encoding                        : Microsoft PCM
Num Channels                    : 2
Sample Rate                     : 44100
Avg Bytes Per Sec               : 176400
Bits Per Sample                 : 16
ID3 Size                        : 38
User Defined Text               : (TXXX) isomiso2mp41
Duration                        : 0:09:42

We can use a tool like Sonic Visualizer to look at the actual waveform of the audio signal

However there is nothing that directly reveals the flag.

Let’s take a look at the spectrogram of the left channel.

To do so I select Pane ⇒ Add Spectrogram ⇒ moanin.wav: Channel 1

We can see this. But I am not quite sure what this should tell me yet.

But I can already tell that it is the same word repeated 3 times.

Now we just need to figure out what this word could mean …

If we now click on Pane ⇒ Add Spectrogram ⇒ moanin.wav: All Channels Mixed

we get the spectrogram of both channels:

From the spectrogram we saw earlier we know that it is one word repeated three times consisting out of 7 letters.

Now we can see what the word should look like.

The first three letters are: gro

and the last two letters are: in

And we can see that there are two letters missing in-between.

It is the 4th and 5th character that is missing.

From the last visible word groa we can see, that the 4th character should be an a.

If we look at the word before groa which is oani we see that the letter a is followed by ni.

And if we look at the first word groin we see that it ends with in.

If we piece these information together we get: groanin.

Here i marked the repeated characters so it is easier to understand

The task description says that the solution is one single word

and we need to wrap it with flag{ } .

So the final flag is: flag{groanin}