There was an audio file that came with the challenge, and I initially couldn't hear any audio. So I was under the impression that I wasn't supposed to hear anything lol.
Confused, I started looking up ways to extract information from audio, and was reminded about the Spectrum Analyzer:
The spectrum analyzer above gives us a graph of all the frequencies that are present in a sound recording at a given time. The resulting graph is known as a spectrogram.
When I initially tried the online version, I couldn't make any sense of the spectogram. A part of it looked vaguely like a flag, but I wasn't sure.
I then remembered/looked up a tool I had used for a challenge in the past called Sonic Visualizer. After downloading it, I opened the sound file there, and added a spectogram. Zoomed in a little bit and there we have the flag for this challenge!
Flag: flag{f8fbb2c761821d3af23858f721cc140b}
More writeups from HacktivityCon CTF 2021