[opus] PLC Sounds Robotic - How to Implement FEC Wideband

Scott Boekweg scott.boekweg at listentech.com
Tue Aug 25 10:21:54 PDT 2015

I am specifically using Celt Wideband (48kHz) over WiFi multicast that naturally leads to lost packets and am trying to minimize the impact to the audio.  I implemented PLC but the audio it produces is robotic.  Have I implemented PLC correctly?

Checking the waveform it is using the previous received waveform to fill in a missing packet but not the full waveform so it has to repeat.   Basically, within a single lost 20ms packet I hear two replicas of the last 10ms of the previous waveform.  Sometimes the repeats are only 4ms long thus repeating 5 times.  This makes it sound robotic.  Is this typical or do I have it implemented incorrectly?  Should it not try to create one replica of the entire 20ms previous waveform instead of having to repeat a portion of it?

Scott Boekweg
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