AAC 5.1: when to move from HE to LC?

[Favorito]

With stereo AAC it's pretty clear when to move from HE to LC, but what about 5.1? It's more complex than stereo. Nero Recode uses 2x formula by default-AVC cinema profile for example automatically sets 80 kbit/s for stereo and 160 kbit/s for 5.1. Maximum HE-AAC bitrate is to 128 kbit/s for stereo and 256 kbit/s for 5.1. According to this 2x thing,we should move to LC at about 160/192. Is it wise?

[check]

depends what your ears say :)

[shon3i]

With stereo AAC it's pretty clear when to move from HE to LC, but what about 5.1? It's more complex than stereo. Nero Recode uses 2x formula by default-AVC cinema profile for example automatically sets 80 kbit/s for stereo and 160 kbit/s for 5.1. Maximum HE-AAC bitrate is to 128 kbit/s for stereo and 256 kbit/s for 5.1. According to this 2x thing,we should move to LC at about 160/192. Is it wise?
For HE-AAC from 96kbps to 200kbps, for LC-AAC everithing upper than 200kbps. You can use 192 LC-AAC, even 160 LC-AAC, but is risky.

Nero automaticly set 160 HE-AAC.

Usual bitrate for 5.1 is 128 HE-AAC, i don't know what is restriction of nero recode, but nero cli, by default encode 5.1 with HE-AAC up to 250kbps

[Favorito]

Thanks for your reply. Is there a way to see how much bitrate is given to each channel? Or maybe calculate somehow.

[shon3i]

I think is Overall Bitrate/number of channels=One Cahnnel bitrate.

ex. 128/6=21.3kbps per channel.

aslo i think LFE uses lower bitrate, but i am not sure.

I dont know how you can see bitrate of each channel.

[Favorito]

LFE should use lower bitrate that's for sure. Also I'm not sure if each channel receives completetly independent bitrates,since a lot of sounds are shared. Remember MP3's joint stereo. Basically,I want to get DVD AC3->AAC quality comparable to 128kbit/s or more LAME MP3, AAC etc. Like almost transparent. Would 256 kbit/s LC-AAC be enough? I know it depends on your ears,but in general.

[shon3i]

Would 256 kbit/s LC-AAC be enough?More than enough.

Remember MP3's joint stereoI am not sure, because that is independent six channels.

You can compress some mono material to 20kbps HE-AAC like one channel in 128kbps 5.1 file, an you will see that sound very good.

[Favorito]

I did some research and found that 2.5x multiplier probably is the most realistic. That is,to get quality compared to 128 stereo: 128x2.5= 320. I agree about HE-AAC. When I first listened to stereo 32 kbps HE-AAC,I was surprised with the quality. However,since I want as good quality as possible at reasonable bitrates,I do not like the effects of HE part,even if they are very small.So 256LC 4me:)

[shon3i]

I did some research and found that 2.5x multiplier probably is the most realisticYes and that rule is only for LC-AAC.

[Favorito]

Yes and that rule is only for LC-AAC.

Yes that rule is for LC. I guess for HE the multiplier should be a bit bigger than 2.5?

[shon3i]

Yes that rule is for LC. I guess for HE the multiplier should be a bit bigger than 2.5?
No, should be smaller, for example 1.5, because 56-64kbps HE-AAC is same as 128kbps mp3. So 160-192kbps HE-AAC 5.1 must have quality as 128 mp3

[Favorito]

Speaking about subjective quality,quite a lot of people often can't ABX properly even 32HE-AAC from 128Mp3 on some music and if they don't know what to look for. In this case,however,when i talked about 2.5x multiplier,I was comparing to the same format. LC to LC and not in between formats. I think HE should have higher multiplier because in HE 5.1 center channel needs more than just stereo/2.