Hello, Jean-Marc Valin
I Make accurate ABX with Audacity
my result is, I audible the highs are smearing, Compare it self!
Using audioequipments are RME Fireface 800 and audio-technica ATH40fs headphones
Test sample (http://www.hydrogenaudio.org/forums/index.php?showtopic=91205)
64kbps is a low bitrate.
(And I will not even ask how can one do an ABX test in Audacity...)
2304p,
Have You done any resampling in the middle of or after the conversion?. There is a symptom of noise shaping in your celt decoded file.
Also not sure if 0.11.2 will be decodable in future. It will be more safe to wait for final specs of Opus.
0.11.2 works more optimally at 48 kHz.
One should expect acceptable quality at 64 kbps but transparency can be achieved at higher bitrates.