[opus] PLC Sounds Robotic - How to Implement FEC Wideband
scott.boekweg at listentech.com
Tue Aug 25 11:15:00 PDT 2015
Thanks Jean-Marc for your prompt response. Yes I am passing the Null so my implementation is correct. Your explanation of how it works helps explain what is going on. So it looks like FEC might be a better option.
After reading through Opus documentation it appears that in-band FEC is not available for Celt, is this correct? Assuming that's correct, is there any recommended documentation on how to implement FEC with wideband Celt? I'm hoping I can pass the "redundant" FEC data through existing RTP packets.
From: Jean-Marc Valin [mailto:jmvalin at jmvalin.ca]
Sent: Tuesday, August 25, 2015 12:02 PM
To: Scott Boekweg <scott.boekweg at listentech.com>; opus at xiph.org
Subject: Re: [opus] PLC Sounds Robotic - How to Implement FEC Wideband
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
> opus mailing list
> opus at xiph.org
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