Opus frequency notching at 15.5 kHz 2018-05-21 05:19:18 Using Opus 1.2.1 and 1.3beta I notice that there is a notch between about 15.5 kHz and about 16.5 kHz that is attenuated by up to -3.8dB from the original source. This effect remains until using a bitrate >= 144 kbps. I can't say it's audible to me, but my hearing sucks above 16 kHz. It seems like cutting the volume of 15.5 kHz frequencies in half would be fairly audible to sensitive ears.This graph was made from Adobe Audition CS6 frequency analysis of the track "Flora's Secret" by Enya. The orange line is the average volume level at each frequency of the source WAV and the blue line is a 96 kbps Opus decoded by opusdec 1.2.1. See the notch at 15.5 kHz. You can also see frequencies above 17 kHz appear boosted over the original. It's as if the line of the original between 15.5 kHz and 19.5 kHz was tilted to the left.Is this effect by design, or at least a known and accepted side effect of "folding" bands?