You can find the challenge here: https://backdoor.sdslabs.co/challenges/MUZ
It seems that vampire is sharing the flag with a few selected people. This file was caught in between transit from one of his people to the other. See if you can recover the flag from it.
After listening to the audio file you hear an ANNOYING sound, but in the background you can hear a voice telling you something. So, we need to get rid of the annoying sound and get straight to the point. We’ll use the process that they use to remove vocals from a track. We’re going to open up the track in Audacity:
We’re then going to split the track. This is possible because the track is Stereo. It would not work with Mono.
Now, we’re going to select the bottom track which is the “Right” and use the Effect “INVERT”
Then we’re going to switch both the top and bottom to mono.
After doing so, you’ll be able to play the track and hear only the vocals.
You know you’ve got it when it starts off “The flag is the SHA256 hash of …”