Need some clearance about aac+ v2

[Selur]

I read some stuff in the forum and over at codingtechnologies.com and I'm a bit confused, or at least not sure if I got it right:

1. aac+ v1 = he-aac = aac + sbr (Spectral Band Replication), right?
2. aac+ v2 = aac + sbr + ps (Parametric Stereo), right?
3. Only available aac+ v2 codecs atm. are the one form winamp (which can be used through dizmons plugin) and the one inside of nero 7, right?
4. aac+ v2 is optimized for the range of 16-40 kbps, right?
5. if saved in some sort of compatibility mode aac+ v1 decoders will playback aac+ v2 material as mono, right?
6. aac+ v2 is ment for stereo only, right?

assuming 1-6 was right I come to the following assumtions:

a. if one wants to encode a stereo signal at a datarate less or equal to 40kBit/s one should choose aac+ v2
b. if one wants to encode a stereo signal at a datarate between 40kBit/s and 96kBit/s one should choose aac+ v1
c. if one wants to encode a 5.1 stream one should choose aac+ v1 (since aac+ v1 is stereo only)
d. if one wants to encode a stereo signal at a datarate above 96kBit/s one should choose 'normal' aac+

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Hope some of you can correct me if I'm wrong somewhere. :)
Btw. are Nero 7, winamp and ffdshow the only decoders out there to handle aac+ v2?

Thx

Cu Selur

[KpeX]

1. Yes
2. Yes
3. Yes, and also a reference encoder somewhere possibly?
4. Up for some debate, but in general, that is the useful range. It's not that the technology has been 'optimized' for this range, it's just that it's not helpful at much higher bitrates (similar to SBR which is not useful at bitrates much more than 100).
5. Correct, no compatibility mode is necessary, however. The PS and/or SBR will be ignored by non-compatible decoders automatically, with the obvious quality hit.
6. Yes, for mono streams PS is useless.

a. Yes
b. Yes
c. PS could be useful for a 5.1 stream. I don't know offhand if any encoders take use of this yet. However, IMO if you care enough about quality to keep all 6 channels you shouldn't be going anywhere near HE-AAC v1 let alone v2.
d. Yes, aka LC-AAC.

All decoders based off a recent version of faad2 can handle HE-AAC v2. This includes most free decoders and nero.

[scharfis_brain]

which modes of AAC will preserve/destroy the phase inyormation of Dolby ProLogic encoded stereo signals?

[KpeX]

All modes that use m/s joint stereo should preserve dpl(ii). AFAIK this is all modes except HE-AAC-v2/PS.

I don't know of anyone that has done any dolby pro logic tests with PS. It would be interesting to see how well it preserves the stereo image in this respect.

[Selur]

thx for the corrections and confimations :)

Reading about dizmons winamp plugin two questions arouse:
1. is aac+ v2 limited to cbr or is it just a weakness of the plugin?
2. does dizmons plugin use ps for 5.1 sound?

Cu Selur

[LoRd_MuldeR]

For which data-rates / profiles one should use PNS ???
Is it intended for low-bitrates only or does it help always?

[Selur]

iirc pns is ment to delete some 'noise' before encoding and add some simulated 'noise' after decoding and if supported by the decoder it should help while using he-aac. (not totally sure about it, since I'm just starting to read up the whole stuff ;))

Cu Selur

[tebasuna51]

I don't know of anyone that has done any dolby pro logic tests with PS. It would be interesting to see how well it preserves the stereo image in this respect.
I make a test and PS (48 Kb/s) don't preserve dolby prologic info.
For dpl I the central channel is ok but the back channel is absolute silence.
For dpl II the central ok but SL and SR sound in all channels.

[scharfis_brain]

until which bitrate the dpl(II) info is being preserved without PS?

Cause I intend to use a 64kbps Audio stream with DPL.
Which encoding options are recommended in this case?

[bond]

btw "aac+" isnt the name for the format in the standard!

"aacplus" (shortcut aac+) is the name of the implementation of the format from codingtechnologies (like divx is one implementation of mpeg-4)

the official name is imho "he-aac v2"

[LoRd_MuldeR]

iirc pns is ment to delete some 'noise' before encoding and add some simulated 'noise' after decoding and if supported by the decoder it should help while using he-aac. (not totally sure about it, since I'm just starting to read up the whole stuff ;))

Cu Selur

Okay. This means it helps when using HE-AAC but is not recommended for LC-AAC, correct?

So, which decoders support PNS? Is the latest version of FAAD from RareWares able to handle PNS correctly?

[Selur]

This means it helps when using HE-AAC but is not recommended for LC-AAC, correct?
As I understood it: yes
So, which decoders support PNS?
see KpeX first post in this thread ;)

until which bitrate the dpl(II) info is being preserved without PS?
If someone knows this, I would like to know that too. :)

Cu Selur

[LoRd_MuldeR]

The post says that FAAD can handle HE-AAC v2, but does this include PNS ???
Somewhere I read FAAD had problems with PNS.What about the current version?

[Selur]

he-aac v2 without pns would be he-aac v1, so when speaking about he-aac v2 pns is included.
http://www.codingtechnologies.com/products/assets/aacPlus_superset.gif
afaik faad2 handels he-aac v2 fine, but I haven't tested it myself.

Cu Selur

[bond]

selur thats wrong!

PNS (Perceptual Noise Substitution) is NOT the same as PS (Parametric Stereo)

[tebasuna51]

until which bitrate the dpl(II) info is being preserved without PS?

Cause I intend to use a 64kbps Audio stream with DPL.
Which encoding options are recommended in this case?
Only PS destroy dpl info, then HE-AAC v2 don't be used.
With HE-AAC v1 (only SBR) the dpl info is preserved. At least 64 Kb/s is recommended.

[scharfis_brain]

so then which encoder(s) is(are) recommended for HE-AAC v1 at 64kbps?

[tebasuna51]

so then which encoder(s) is(are) recommended for HE-AAC v1 at 64kbps?
You can search in http://www.hydrogenaudio.org/forums/ for quality test. I don't know recent test including Winamp 5.1 and Nero 7 encoders.

On the other hand, talk about fixed bitrates is only for reference, you know the better quality is obtained with vbr settings and the exact final bitrate can vary very much with the source.

[LoRd_MuldeR]

Sure SBR and PNS are differnet things.

So again: FAAD can handle AAC+SBR (HE-AAC) and even AAC+SBR+PS (HE-AAC V2), but what about PNS? It seems to decode AAC files encoded with PNS, but I'm not sure about the quality...