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Topic: AAC+ . Will it be High quality? (Read 7471 times) previous topic - next topic
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AAC+ . Will it be High quality?

With the new codecs for Nero by Mausau, I started to make some tests, and was a bit dissapointed by the mp3pro "highest" quality setting.

This made me think if AAC+, which makes use of SBR as well, will have the same faults. (I suppose Ivan could reply this already), or one should stick with (plain) AAC for quality?



To illustrate this a bit, here there are some samples:

Nero mp3PRO (163KB) (rename to .mp3)
LAME 3.91 --alt-preset 128 (168KB) (rename to .mp3)
Nero AAC (MP4) Normal(227KB) (rename to .mp4)

mp3PRO File is made with the settings:
encoding quality : highest
variable bitrate : highest
allow IS
allow downmix
padding ISO
(dissallowing IS and downmix doesn't make differences in sound)

AAC File is made with the settings:
Variable bitrate : Normal::High
Quality : Highest
Profile : LC

The mp3pro file is, maybe, less annoying than the lame ABR one (mostly because of the dropouts in the latter) but still sounds bad. Just compare it to the AAC file.

Btw: Here's the original sample file in .flac . Ivan, if you have a working AAC+ encoder (and decoder), could you provide a sample to see how it will sound? (that is, encode it, decode, and put the aac+.flac online) : FLAC (1.26MB)

[Edit: Grammar]

AAC+ . Will it be High quality?

Reply #1 –
mp3pro is great at low bitrate (50-80 kbps). At 120 kbps, there are more artifacts than with a lame ABR preset.

AAC+ . Will it be High quality?

Reply #2 –
also I've heard that vbr doesn't really improve quality with mp3pro much, and can damage it.

AAC+ . Will it be High quality?

Reply #3 –
Uhm. VBR does help mp3Pro at lower bitrates. Never tested high bitrate, since it's not meant for it.
Juha Laaksonheimo

AAC+ . Will it be High quality?

Reply #4 –
I tried with VBR, because this way it uses up to 144kbps [Edit: 160kbps actually] frames, whereas the Constant bitrate only goes up to 96kbps (at least the codec in nero).

What is mostly noticeable in this sample, is a sensation of filtering, and missing highs (which corresponds to SBR), appart of the artifacts. It make it sound a bit empty.

Quouting JohnV:
> Uhm. VBR does help mp3Pro at lower bitrates. Never tested high bitrate, since it's not meant for it.

AAC+ is targeted at low bitrates as well, isn't it?

AAC+ . Will it be High quality?

Reply #5 –
Quote
,Apr 14 2003 - 12:39 AM]What is mostly noticeable in this sample, is a sensation of filtering, and missing highs (which corresponds to SBR), appart of the artifacts. It make it sound a bit empty.

Just to make sure: Always remember to use mp3pro with mp3pro capable player/decoder. Otherwise you'll definitely get "a sensation of filtering and missing highs", since normal mp3 player/decoder doesn't output over 10khz frequencies.

I hope the mp3pro encoder doesn't use Instensity Stereo even though it is allowed, because it can definitely lower the quality at higher bitrates. Just in case this should be never checked for higher bitrates (though who uses Mp3Pro anyway at high bitrates?)

Anyway, just to be sure everybody is testing correctly mp3pro decoded file, the mp3pro decoded wav is available here.

Quote
AAC+ is targeted at low bitrates as well, isn't it?
Yep.
Juha Laaksonheimo

AAC+ . Will it be High quality?

Reply #6 –
Quote
,Apr 13 2003 - 10:34 PM] This made me think if AAC+, which makes use of SBR as well, will have the same faults. (I suppose Ivan could reply this already), or one should stick with (plain) AAC for quality?

Please use the search function of this board or read the Wiki pages on Audiocoding.com about the purpose of SBR.

Quote
The mp3pro file is, maybe, less annoying than the lame ABR one (mostly because of the dropouts in the latter) but still sounds bad. Just compare it to the AAC file.


Basically you're comparing apples and oranges here, because Nero AAC -normal results in 227 KB file size which is about 40% bigger than the mp3PRO file. Do a comparison at ~64-96 kbps for all three codecs which would be much fairer to the objectives of the mp3PRO format.
ZZee ya, Hans-Jürgen
BLUEZZ BASTARDZZ - "That lil' ol' ZZ Top cover band from Hamburg..."
INDIGO ROCKS - "Down home rockin' blues. Tasty as strudel."

AAC+ . Will it be High quality?

Reply #7 –
AFAIK, AAC+ does not uses SBR at high bitrates, "where encoder has enough space".

AAC+ . Will it be High quality?

Reply #8 –
Quote
Just to make sure: Always remember to use mp3pro with mp3pro capable player/decoder. Otherwise you'll definitely get "a sensation of filtering and missing highs", since normal mp3 player/decoder doesn't output over 10khz frequencies.


Of course. I used Thompson mp3pro plugin for winamp, as well as listening directly via Nero wave editor. I was mentioning "holes" in the high frequencies, probably because it estimates it to be not audible, but surely is.

Quote
Please use the search function of this board or read the Wiki pages on Audiocoding.com about the purpose of SBR.

I suppose you mean this sentence (written by yourself):
Quote
SBR means "Spectral Band Replication" and is used with AAC (called aacPlus or AAC+ then) or MP3 (called mp3PRO) to increase the coding efficiency of these standard codecs, but only for low bitrates around 20-64 kbps for AAC and 32-96 kbps for mp3PRO, as it will not help for higher bitrates when the codecs have sufficient headroom to encode the high frequencies without SBR

This is wrong, at least for mp3PRO.
An mp3PRO stream is a MPEG2 Layer 3 stream, which has a range from 8 to 160kbps, and a sample rate of 16, 22.05 or 24KHz ( I am sure you're aware of this ).
Since the MP3 Part only encodes half of the spectrum ( up to 11Khz if the file is sampled at 44Khz), the SBR part has to do the rest (11...22Khz), even up to 160kbps. And it doesn't seem to be efficient in my sample.

If it is going to work the same way with aac+ (which is what I don't know), I expect similar results, which means: useless for High quality.

Quote
Basically you're comparing apples and oranges here, because Nero AAC -normal results in 227 KB file size which is about 40% bigger than the mp3PRO file.

I was not comparing the quality of the mp3PRO against AAC. That's why I supplied the Lame one, and just to show that it's a small improvement in that range.
I put the AAC just for a sample of how it should sound. I suppose downloading 200KB is nicer than the 1.2MB of the .flac file.

Quote
AFAIK, AAC+ does not uses SBR at high bitrates, "where encoder has enough space".


That's my question and my worries. Will that be true, or not. I think I should read the papers of AAC+, but I searched for an "easier answer" here. In mp3PRO, the SBR is never bypassed.

AAC+ . Will it be High quality?

Reply #9 –
Quote from: [JAZ
,Apr 14 2003 - 10:00 AM] I suppose you mean this sentence (written by yourself):
Quote from: ></span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>[b
QUOTE[/b] </td></tr><tr><td id='QUOTE'><!--QuoteEBegin-->
SBR means "Spectral Band Replication" and is used with AAC (called aacPlus or AAC, then) or MP3 (called mp3PRO) to increase the coding efficiency of these standard codecs, but only for low bitrates around 20-64 kbps for AAC and 32-96 kbps for mp3PRO, as it will not help for higher bitrates when the codecs have sufficient headroom to encode the high frequencies without SBR
<!--QuoteEnd]
This is wrong, at least for mp3PRO.

Not really.

CT, at the beginning, decided that would add SBR support for bitrates only up to 96kbps. (That's why old versions of the Nero MP3pro plugin supported only up to that)

Later, they decided to support the entire MPEG2layer3 bitrate range. Don't ask me why, IMO wasn't a wise idea anyway.

AAC+ . Will it be High quality?

Reply #10 –
OMG! The quote bug again. :-P

AAC+ . Will it be High quality?

Reply #11 –
Quote
Not really.

CT, at the beginning, decided that would add SBR support for bitrates only up to 96kbps. (That's why old versions of the Nero MP3pro plugin supported only up to that)

Later, they decided to support the entire MPEG2layer3 bitrate range. Don't ask me why, IMO wasn't a wise idea anyway.

I'm not sure what you are saying with that.
I could understand that they though that 128kbps didn't need SBR because with MPEG1 Layer 3, it sounds "good enough", but since a mp3PRO file is a MPEG2 Layer 3, the SBR needs to generate the remaining frequencies after all.

The question about AAC+ still remains unanswered.




Side note: Now I've encoded with CBR 96kbps Stereo and it sounds like the VBR file made before (haven't done an abx though).

AAC+ . Will it be High quality?

Reply #12 –
SBR is useful of reconstructing frequencies from ~5 kHz up to 20 kHz

SBR range and base codec frequency range depend on the few important parameters, like desired base codec bit rate,  expected distortion, etc..

When codec is able to cover high frequency range with acceptable perceptual distortion (like MP3 @ 128 kbps) there is no need for SBR.

This "border" frequency is no rocket science.  For Nero Digital  implementation of High Efficiency AAC  it still has not been decided what will be the maximum SBR bit rate,  but  according to internal tests done so far,  there is no need for SBR beyond ~90 kbps for AAC.  I will probably left SBR option for 96 kbps, if people want to have full bandwidth files at that bitrate, instead of standard 14.5 kHz AAC bandwidth.

At 128 Kbps / 44.1  kHz / Stereo, for AAC,  I don't see any particular use of SBR.  During the SBR standard development, there have been options to use single-rate SBR mode, and in that case it would be interesting to use SBR to cover frequency ranges between 16 kHz and 22.05 khz for, say, 128 kbps  stereo.  But I think this has been canceled from the final proposal for SBR - I have to check.

And, finally,  the purpose of SBR is not to generate perceptually identical result,  its purpose is to have best possible quality at very low bit rates.

See:  http://www.m4if.org/public/documents/vault...4-out-30034.zip

AAC+ . Will it be High quality?

Reply #13 –
Now I'm half clear, half confused. Using SBR won't guarantee perceptual transparency. But.. aac+ will use ALWAYS SBR or are you saying that, unlike mp3PRO, it can be gradually used?

Seems you're saying that it is a "On or Off" thing.


Edit: AAC+ *might* be the successor of DAB/MP2 (DRM and XM-Satellite) and AC-3 (Nero Digital is in that direction). That's why I am a bit worried about quality.

AAC+ . Will it be High quality?

Reply #14 –
Well, strictly speaking - I don't think that AAC encoders will allow switching of SBR between frames,    because  that would require switching of the sampling rate as well  if you want to get high frequencies with AAC (SBR AAC uses  half of the total sampling rate for AAC core)

Single rate SBR would theoretically allow that, but it has been removed from the specs.  I don't think it was effective either.

What is sure,  there are many possibilities, and we are evaluating all of those.


Btw - high bit rate AAC [without SBR] will always be available 

AAC+ . Will it be High quality?

Reply #15 –
Quote
Well, strictly speaking - I don't think that AAC encoders will allow switching of SBR between frames,    because  that would require switching of the sampling rate as well  if you want to get high frequencies with AAC (SBR AAC uses  half of the total sampling rate for AAC core)

Can be done by resampling the frames without SBR as well.
But it is disallowed by the standard.

Menno

AAC+ . Will it be High quality?

Reply #16 –
Is there any info on how SBR will be handled in the Nero AAC plugin when encoding at variable bitrate?
Like, would it only be used for anything < normal for example?
Thanks

AAC+ . Will it be High quality?

Reply #17 –
I was wondering if there is a better insider news source than HA concerning AAC development? I mean compared to Ogg- and mp3-sections Tech (AAC) is dead
"There's nothing as pathetic as an aging hipster."

AAC+ . Will it be High quality?

Reply #18 –
AAC is usually more heavily discussed (mainly by Hans-Jürgen, Menno and me) at www.audiocoding.com/phorum . It's the forum where the AAC techie people hang out.

AAC+ . Will it be High quality?

Reply #19 –
Thanks for the board info! Shame on the white font on grey background, my laptop LCD doesn't like that (makes it almost unreadable) 
"There's nothing as pathetic as an aging hipster."