Audio Quality: What is call distortion?



Call Distortion, usually described as Synthetic or Robot-like voice, is almost always due to a high rate of packet loss or packet discard due to jitter. 

The packet loss concealment algorithms used in Voice over IP systems are able to deal with occasional packet loss but when the rate of loss is very high then they can lead to robotic sounding voice. Robotic sounding voice occurs when a large number of packets are dropped, the packet loss concealment algorithm is not able to compensate. VoIP systems use Packet Loss Concealment (PLC)  to deal with small amounts of packet loss. The most common type is a replay algorithm. A replay algorithm replays the last sound packet received to help fill in the gaps. But when multiple consecutive packets are lost, this method gives the voice the same characteristics of synthesized or robotic speech.


The best way to resolve this is to identify the source of packet loss or jitter problems. This is usually the Internet connection. You can use our VoIP test to test this. Try to test it while an issue is happening. A qualified network technician can do more strenuous testing if needed.

Questions to answer:

  • When are the bad calls happening? - Could the issue be happening when a scheduled download is happening? Or if your Internet connection is shared like cable or DSL, it may be happening when kids come home from school.
  • Who heard the distortion? If you did not hear it but the customer did, it could be the upload section of your Internet connection.
  • Was the call inbound or outbound? Does it happen on both?
  • Was the User on speaker phone or headset? Check volume or replace headset.
  • Was this during a conference call? Conference calls can cause trouble all by themselves and it can be anybody on the call causing it.
  • Was one of the callers on a mobile phone? (Mobile phones can have delay issues)
  • Is the issue repeatable or is it sporadic? (Can it be replicated on demand?)
  • Is it happening to everyone or only a few users? (Could be a bad network segment or bad phone)

Let us know your experiences in the comments below. Maybe we can all help each other.

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