# Make a Difference Write-up

> From: VolgaCTF 2024 Qualifier
> What's that noise?
>
> File: make_a_difference.wav
>
> Solved by: Jackylkk2003

## The file attached

It is a *stereo* wav file.


## Observations

2 main observations here:

* The 2 tracks seem to be the same.
* The challenge title suggests 'difference'

## Solution

We can try to subtract the tracks to see the differences, we can follow the writeup [here](https://ctftime.org/writeup/8835).

We now have a transformed audio.


It looks a bit like morse code, but we cannot determine how to split the characters.

Also, for clearer view, we can investigate the spectrogram.


Again, by some guessing, or reading [writeups](https://ctftime.org/writeup/29028), you will know that these represents binary.

We encode the short sounds as 0 and long sounds as 1, we will get the following binary string:

`0101011001101111011011000110011101100001010000110101010001000110011110110011000001111000011001010011010100110110001100010011001100110011011001000110001001100100011000110011011001100100001110000011100000110010001110010110000100110111011000010110010000110111001110010011010000110010011001010011100101100011011001000011000000110010001110000011001101111101`

Which represents the flag: `VolgaCTF{0xe56133dbdc6d8829a7ad7942e9cd0283}`

The remaining question is: How to get the binary string?

Well, I just manually do it, using my eyes and hands without any more tools. A sad thing happened during the transcription is that I made some error during the transcription and has to redo it. It is very tedious.

With enough hard work, we can finally get the flag.