[opus] Opus application_mode==AUDIO, 20ms framing issue?

[Kevin Connor]

Hi Opus list, 

  I'm noticing a discontinuity in the quality between use of 10ms and 20ms framesize for mode=AUDIO  at a bitrate of about 28000.    Quality drops audibly for voice signals when encoded at 20ms framesize, versus quality at 10ms.   This effect is mode=AUDIO only.   Using mode==VOIP shows no sig. difference between 10 and 20ms framing at this bitrate.      Pesq totally overreacts, as it is wont to do :)   However, I do hear a slight drop. Admittedly, 28kbps is a low bitrate to be running in mode=AUDIO.     Is this effect known?  Is there a difference in processing with audio mode between 10ms and (other framesizes)?   I reckon it will go away if I throw some more bitrate at it,  but wanted to understand it a bit better.

Thanks very much, KevinC