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

Jean-Marc Valin jmvalin at jmvalin.ca
Tue Aug 25 11:02:01 PDT 2015

What do you mean by "implement"? You're just using the Opus built-in PLC
(passing NULL), right? The PLC generally attempts to find periodicity
and replicate it. I guess if your signal isn't periodic it can lead to a
repetition that isn't great. It's something that could probably be
improved in the PLC.



On 08/25/2015 01:21 PM, Scott Boekweg wrote:
> 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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