First, use SSTV decoder to decode the audio to an image. This image has a `rot13` flag on the top left.

```py
# Tool used: SSTV decoder - Android
# The flag is in the image
text = 'QHPGS{UHZOYR_Z3Z3_1BEQ}'

def rot13(text):
rot = ''
for i in text:
if i.isalpha():
rot += chr((ord(i) - ord('A') - 13) % 26 + ord('A'))
else:
rot += i
return rot

flag = rot13(text)

print(flag)

# DUCTF{HUMBLE_M3M3_1ORD}
```