I have some questions about AAC-HE.

So I hear that it's largely targeted towards ultra-low bitrates >64kbs. Any chance that sometime in the future AAC-HE could be made competetive with LAME/NERO ~160 kbs? I mean, with it, could it be possible to get perfect audio out of tiny tiny files? Or does it have a low "ceiling" of fidelity?

Is it included in Nero AAC? I notice on some of my songs the bitrate sometimes dips as low as 80 (0.45). Can it be mix/matched with AAC-LC?

Can anyone explain better how it works?

thx

it already competes with LAME at the same bitrate, and is superior in some spots here and there because it's a modern codec and has a lot to be improved while LAME stressed stability... like I read in some listening test, all codecs now are very difficult to distinguish with normal music at 128kbps...

HE-AAC is able to compete with Lame and LC-AAC at bitrates of 80kbps and below. HE-AAC doesn't benefit from high bitrate encoding. That is why you should use HE-AAC for encoding files at 32kbps to 80kbps. Anything higher and you should use LC-AAC. There are actually two different versions of HE-AAC and I think version 1 is better for 32kbps - 48kbps encoding while version 2 is better for bitrates between 48kbps to 80kbps. HE-AAC encoding is written into Nero's AAC encoder. It only goes into affect if you choose lower -q values. -q0.45 isn't low enough, you need to choose a -q value of somewhere around -q0.25. Nero's encoder is smart enough to choose whether or not the encoding needs HE-AAC and which version of HE-AAC to use. You can force Nero to use HE-AAC encoding and you can force it to use a certain version.

Either way, HE-AAC doesn't benefit from encoding at bitrates above 80kbps. Since you are looking at 160kbps encoding, you might as well just stick with Lame at -V 4 --vbr-new or go with Nero AAC at -q0.45. You can search this site and wikipedia for more information about how HE-AAC works. It is very, very similar to mp3pro though.

One correction: HE-AAC version 1 incorporates SBR and target bitrates are 48-80kbps, version 2 incorporates SBR and PS (Parametric Stereo) and target bitrates are 24-48kbps.

Thanks, I couldn't remember. I had a feeling that I switched things around but I couldn't remember and my internet has been acting up so I couldn't really look at the AAC wiki page. Either way target bitrates of 160kbps are too high for HE-AAC. Thanks for clearing things up though.

Thanks muaddib for sorting that out. I just got myself a new cell phone (Sony Ericsson) which can play HE-AAC both version 1 and 2 (I'm pretty sure). I read from the last AAC listening test @ 48 kbps that ABR was used and that v1 was preferred over v2 (at that time and at that bitrate).

Would you say that ABR is still preferred over VBR at 48-64 kbps and that v1 still has the edge at that bit range?

Thanx

Downsampled SBR is a potential candidate in such context. However, I'm not sure if it's really worth it (from an engineering POV), considering that it implies using an SBR decoder over just a plain LC decoder.

At 64kbps v1 is expected to be better. For 48kbps I would suggest doing listening test and deciding yourself what you prefer, something might then sound better with v1 something with v2. ABR or VBR depends on specific implementation.

yeah, from reading about it, it appears that he-aac does have a low fidelity ceiling, because it uses data from low freq's to guess what the high-freq's should be.

Still, it should be really useful for things like audiobooks where quality isn't that important.

Oh, and I just did encode my music library via nero aac 0.45. Man that took forever.