Original writeup has images and description of decoding.

## Solution script

```python
wav = wavio.read('FAM.wav')
wavio.write('rectified.wav', abs(wav.data), wav.rate)
l = [(a-2*b+c) / float(b) for a,b,c in zip(wav.data[:10000], wav.data[1:], wav.data[2:])]
print bitarray.bitarray([0]+[int(e<-0.25) for e in l][10::20]).tobytes()
```

Original writeup (https://hackingforsoju.team/blog/write-up-inshack-2019-lit-fam/).