• AAC-HE (Nero, CBR 80 “high”): very disappointing score, for this format claimed to be a killer at low bitrate. 80 kbps is probably excessive for AAC-HE, now that AAC-LC implementation are getting better and better (take a look again on POOL#1, and see how AAC-LC have progressed). AAC-HE doesn’t suffer from any lowpass, but the SBR layer is highly impure, and seems to interfere with the lowest part of the spectrum. As result I get constant artefacts, noticed with more than 90% of the tested samples. AAC-HE has a maybe CD spectrum, but it’s like if a cricket was directly screeching in my headphones. Personally, I would consider something poorer (with audible lowpass and some ringing) as better that this (un)constant parasitical noise. Just a personal appreciation; other people might prefer the opposite – I don’t know. AAC-HE also have *big* troubles with attacks (pre-echo) and fine details (smearing), even more audible than simple MP3. AAC-HE would probably more pertinent at lower bitrate, for which other contenders would probably be in pain.
• AAC-LC (iTunes, CBR 80): poor results. I’ve expected something better, a bit more suitable for listening with portable player. Quality is not *that* bad (just compare to MP3 or WMA for reference), but there are too often irritating distortions. Lowpass is also annoying, at least on ABCHR conditions (with direct comparison with a full quality reference file), probably less perceptible on common earbuds (I’ve tried, and quality suddenly became much less irritating).
• Vorbis (aoTuV beta 4, VBR –q 0,9): this is by far the most enjoying thing I’ve heard at this bitrate. I was highly surprised by results I’ve got with the 150 classical samples; I was literally astonished by the final score obtained with the 35 remaining samples! Vorbis is obviously an amazing tool at this bitrate. Or differently: Vorbis apparently embed some encoding tools (point stereo?) which are remarkably suited for this bitrate (but which are maybe interfering too much at higher bitrate: see this test and this test).
Quality is not perfect of course; usual vorbis problems are here: noise boost, coarseness, fatness. Distortion (vibrating effect) on long tonal notes also occurs. But these issues are limited (at least compared to other mutilations produced by other encoding tools at this bitrate) and I would say that Vorbis at this bitrate could be pertinently used for portable playback by people which are not excessively hard to please and more interested to maximize the capacity of their flash memory digital player. It’s too bad for me that vorbis performances are not as good with classical as with “various music”. But even on this “Achilles’ heal”, vorbis outperforms current other encoding tools.