Bibliography (7):

1. SonarSnoop: Active Acoustic Side-Channel Attacks

2. Speech2Face: Learning the Face Behind a Voice

3. Hearing your touch: A new acoustic side channel on smartphones

4. Hard Drive of Hearing: Disks that Eavesdrop with a Synthesized Microphone

5. Wikipedia Bibliography:

   1. https://en.wikipedia.org/wiki/Voice_over_IP  :

      https://en.wikipedia.org/wiki/Voice_over_IP

   2. https://en.wikipedia.org/wiki/Variable_bitrate  :

      https://en.wikipedia.org/wiki/Variable_bitrate

   3. Hidden Markov model