That comparison appears to says that the difference in quality between opus and he-aac is the same as the difference between he-aac and vorbis.
Opus is definitely better, but we have basically hit the wall in audio compression (we'll need a serious breakthrough to go much farther). There also isn't as much interest in audio codec research because even very large raw audio files pale in comparison to fully compressed video.
Incremental improvements are happening in opusenc, current status (as of 1.2 and 1.3-beta) is that musical content is generally transparent at ~96kbps VBR, with a few needing ~128kbps and a tiny minority needing ~160kbps.
The developers are slowly reducing the required bitrate for transparency, it wouldn't surprise me if they reach transparency at ~64kbps VBR in a year or two.
Generally Transparent = MP3 LAME @ ~ 128kbps. That is the good old standard.
There has been PR and marketing materials, much like Video Codec making claiming they are 50% better then H.264 or AVC or whatever. AAC or MP3Pro even claim to be MP3 128kbps quality at 64Kbps. Of course which never happened even after years of fine tuning.
Opus is the first and only codec in years, or decades that had better music quality then MP3 @ 96Kbps. Even AAC cant do that, at least not in majority of cases.
I have come to the conclusion that Audio compression has come to end of the S curve, with diminishing returns. It literally took us all the years till all MP3 patents has expired to get an Audio codec that is better at it with 20% less bit rate.
I very much doubt we could have 64Kbps VBR to sound better without many more breakthroughs.
>Generally Transparent = MP3 LAME @ ~ 128kbps. That is the good old standard.
Says who? And which version of LAME? That encoder has seen huge improvements over the years. We should not define audio transparency by an outdated and flawed format. We should define audio transparency by whether it is distinguishable from a lossless source or not.
But yes, a modern version of lame (3.98 or newer) will be transparent around V5 VBR, which is ~130kbps. BUT -- and this is a huge twerking 'but' -- the MP3 format suffers from pre-echo. There is nothing you can do about it. It is lessened at higher bitrates, but you can never completely get rid of it. There is also the problem of the SFB21 defect, which can severely bloat the allocated bitrate on content that is heavy in high frequencies: http://wiki.hydrogenaud.io/index.php?title=LAME_Y_switch
Newer formats such as AAC, Vorbis and Opus do not share these limitations. I don't know where you read that AAC is worse than MP3, because that is simply objectively false, as shown by every listening test you can care to dig up. Did you mistakenly use FAAC (probably the worst AAC encoder out there) or something?
I would highly recommend that you give it a go yourself. Take a FLAC source, encode Opus files yourself. The encoder is freely available from https://opus-codec.org/downloads/ and integrates nicely into Foobar2000's converter function (Opus is already there as a profile, it will ask for the location of opusenc.exe the first time you use it).
Use the ABX Comparator plugin for Foobar2000 (both available from http://foobar2000.org) and run a few trials.
After all, public listening tests are one thing, but to be absolutely sure a format/bitrate is transparent to you, individual testing is needed.
I have run a number of tests myself (of Opus and other formats) and found general transparency at ~96kbps Opus, lower for some tracks. For those tracks that weren't transparent at that bitrate, the artifacts were generally benign and not that annoying (slightly increased noise levels, mostly).
Opus is definitely better, but we have basically hit the wall in audio compression (we'll need a serious breakthrough to go much farther). There also isn't as much interest in audio codec research because even very large raw audio files pale in comparison to fully compressed video.