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48 kbps AAC Encoders Test - Q1 2006 Edition
NoXFeR
post Dec 15 2005, 02:00
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Well, in my opinion, the test should be about how good 48 kbps really can be using recent codecs, and as such VBR should be used, and ABR where VBR isn't appropriate.

Edit: Phrasing
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guruboolez
post Dec 15 2005, 10:35
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[JAZ] & Serge Smirnoff> I know that 48 kbps stream exists; the problem is that several 56K users can't listen to them. Ask Roberto; he planned to test 48 kbps after his last 128 multiformat test. But several members told him that 48kbps couldn't be properly read with low (56K) connection. Then he switched to 32 kbps as target for his listening test.
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IgorC
post Dec 15 2005, 14:54
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So you are pruposing a 32 kbit/s test, right?
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guruboolez
post Dec 15 2005, 15:01
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QUOTE (IgorC @ Dec 15 2005, 02:54 PM)
So you are pruposing a 32 kbit/s  test, right?
*

At all. I just wonder about the choice of testing CBR or ABR -- or any controlled bitrate allocation encoding mode -- over VBR. The arguments I saw don't make sense to my mind.

I could understand why CBR/ABR is privileged over VBR for low bitrate encoding: bitrate must be controlled for streaming. But I don’t know any form of internet connection which could handle CBR 48 kbps but not VBR 48 kbps. Either you have a 56K or less, or you have 128K or more. I don’t know anything between. With 128K, you can safely stream 48K with huge bitrate peak. With 56K, streaming 48 kbps file, even at constant bitrate, is unlikely.

VBR could be discarded for the sake of “predictable size”. It’s indeed interesting for DVD backup (you proposed it, IgorC). But if the purpose of the test is DVD ripping, it wouldn’t make sense to use 44.1@PCM samples when all DVD are using 48KHz sampling rate and are rarely providing LPCM stereo tracks (but rather lossy encoded signal). A “DVD backup listening test at 48 KHz” would interest many people, but then, the chosen samples should obviously be in relation with the object of the test: several speech samples (with and without music), 48 KHz, high dynamic (both loud and very quiet samples) and last but not least AC3 and/or DTS samples as source. We can’t use the worst samples of previous listening tests as Ivan proposed it.

Both arguments (streaming and DVD backup) are going against either the selected bitrate (48 Kbps vs streaming) or the possible application of the test settings (DVD Video ripping vs samples coming from CD Audio). We need some coherence. Are we looking for the best AAC setting in this pre-test? If the answer is positive, then it won’t make sense to discard VBR. Or does someone suddenly dispute the well-known fact that VBR is better than ABR/CBR? If not, if VBR encoders are available and if we’re starting a pre-test for 48 kbps encoders/profile, then we should at least give a try to existing VBR encoders. If we have to discard one encoder/setting (e.g. to limit listening fatigue), it would rather be a CBR one because they’re well-known to provide inferior quality to VBR encoding mode. ABR/CBR are maybe better than VBR at this bitrate, but if someone is tempted to claim this, he should prove it (the burden of the proof lies on people making unusual claims, and VBR<CBR is clearly unusual; so it must be proved – cf. TOS#8).

Therefore, I can't see any valid reason to discard VBR from such test.
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IgorC
post Dec 15 2005, 15:09
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It was mentioned 48 kbit/s is very interesting to tests because it´s a highest bitrate for PS. So it test also to evaluate PS.

Guru you already choosed a bitrate that you want 80 - 180 kbps in your previous test. When people asking you to do some test at 48-64 kbit/s you said it´s not interesting for you. So let to us to see some result on 48 kbit/s smile.gif
You always have choosen a bitrate what you want and now you want that we all hear you always.

This post has been edited by IgorC: Dec 15 2005, 15:13
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JohnV
post Dec 15 2005, 15:21
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QUOTE (guruboolez @ Dec 15 2005, 05:01 PM)
QUOTE (IgorC @ Dec 15 2005, 02:54 PM)
So you are pruposing a 32 kbit/s  test, right?
*

But I don’t know any form of internet connection which could handle CBR 48 kbps but not VBR 48 kbps. Either you have a 56K or less, or you have 128K or more. I don’t know anything between. With 128K, you can safely stream 48K with huge bitrate peak. With 56K, streaming 48 kbps file, even at constant bitrate, is unlikely.
*


One area for 48kbps would be mobile streaming in GSM EDGE and 3G -networks.

This post has been edited by JohnV: Dec 15 2005, 15:21


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guruboolez
post Dec 15 2005, 15:21
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QUOTE (IgorC @ Dec 15 2005, 03:09 PM)
It was mentioned 48 kbit/s is  very interesting  to tests because  it´s a highest bitrate for PS. So it test also to evaluate PS.

Guru you already choosed a bitrate that you want  80 - 180 kbps in your previous test. When people asking you to do some test at 48-64 kbit/s you said it´s not interesting for you.  So let to us to see some result on 48 kbit/s  smile.gif
You always have choosen a bitrate what you want and now you want that  we all hear you  always.
*

It seems that you don't understand. I have nothing against the choice of bitrate. I just can't see any valid reason TO NOT USE VBR. Is it clearer? wink.gif
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guruboolez
post Dec 15 2005, 15:22
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QUOTE (JohnV @ Dec 15 2005, 03:21 PM)
QUOTE (guruboolez @ Dec 15 2005, 05:01 PM)
QUOTE (IgorC @ Dec 15 2005, 02:54 PM)
So you are pruposing a 32 kbit/s  test, right?
*

But I don’t know any form of internet connection which could handle CBR 48 kbps but not VBR 48 kbps. Either you have a 56K or less, or you have 128K or more. I don’t know anything between. With 128K, you can safely stream 48K with huge bitrate peak. With 56K, streaming 48 kbps file, even at constant bitrate, is unlikely.
*


One area for 48kbps would be mobile streaming in GSM EDGE and 3G -networks.
*


Doesn't it work with VBR? Is streaming already available for mobile?

This post has been edited by guruboolez: Dec 15 2005, 15:22
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JohnV
post Dec 15 2005, 15:24
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QUOTE (guruboolez @ Dec 15 2005, 05:22 PM)
Doesn't it work with VBR? Is streaming already available for mobile?
*
Should work yeah. I didn't comment against or for VBR, just mentioning one area of use for 48kbps streaming.

This post has been edited by JohnV: Dec 15 2005, 15:24


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IgorC
post Dec 15 2005, 15:26
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QUOTE (guruboolez @ Dec 15 2005, 06:21 AM)
It seems that you don't understand. I have nothing against the choice of bitrate. I just can't see any valid reason TO NOT USE VBR. Is it clearer? wink.gif
*


So why you´re insisting to change bitrate? 32 kbbs ....

This post has been edited by IgorC: Dec 15 2005, 15:27
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IgorC
post Dec 15 2005, 15:33
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I don't agree to use VBR at least for high anchor. For 48 kbps VBR high peak isn't problem but for 128 kbit/s VBR there will be higher peak like 160-180 kbps. It is impossible to stream at 128 kbit/s.
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IgorC
post Dec 15 2005, 15:39
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QUOTE (Gabriel @ Dec 14 2005, 09:43 AM)
The mp3 cbr is very restricted, as the bit reservoir is only 4088 bits. The AAC reservoir is way higher


So why we should give a prior for mp3? If mp3 is based on old tech and AAC is more flexible. It's only problem for mp3 and not for AAC.

I.e if codec support more advanced features and other no, it´s not reason to disable them.

The same thing happening with video. Some h.264 codecs still doesnt support High Profile but only main profile. So it´s not reason to test all h.264 codecs as they were main profile.

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ATWindsor
post Dec 15 2005, 16:15
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QUOTE (IgorC @ Dec 15 2005, 06:26 AM)
QUOTE (guruboolez @ Dec 15 2005, 06:21 AM)
It seems that you don't understand. I have nothing against the choice of bitrate. I just can't see any valid reason TO NOT USE VBR. Is it clearer? wink.gif
*


So why you´re insisting to change bitrate? 32 kbbs ....
*



His not insisting on changing the bitrate, he's saying that "if we are not to use VBR because we are testing for streaming, why are we testing a bitrate that is not a good choice for streaming (48 kbps)

AtW
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Gabriel
post Dec 15 2005, 16:20
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QUOTE
So why we should give a prior for mp3? If mp3 is based on old tech and AAC is more flexible. It's only problem for mp3 and not for AAC.

I.e if codec support more advanced features and other no, it´s not reason to disable them.

I just meant that in CBR for such low bitrates, AAC is not as restricted as MP3 is.
It did not implied that this would be a justification to restrict AAC to cbr.

To me 48kbps is a streaming bitrate, and streaming must be cbr. However, it can feature a big buffer if increased decoding delay is acceptable.
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guruboolez
post Dec 15 2005, 16:24
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QUOTE (IgorC @ Dec 15 2005, 03:26 PM)
QUOTE (guruboolez @ Dec 15 2005, 06:21 AM)
It seems that you don't understand. I have nothing against the choice of bitrate. I just can't see any valid reason TO NOT USE VBR. Is it clearer? wink.gif
*


So why you´re insisting to change bitrate? 32 kbbs ....
*


blink.gif
Could someone explain him?

EDIT: ATWindsor did smile.gif

This post has been edited by guruboolez: Dec 15 2005, 16:25
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guruboolez
post Dec 15 2005, 16:27
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QUOTE (IgorC @ Dec 15 2005, 03:33 PM)
I don't agree to use VBR  at least for high  anchor.  For 48 kbps VBR high peak isn't problem but for 128 kbit/s VBR there will be higher peak like  160-180 kbps. It is impossible to stream at 128 kbit/s.
*

High anchor is here for reference; not to reflect a practical purpose.
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IgorC
post Dec 15 2005, 17:36
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QUOTE (guruboolez @ Dec 15 2005, 07:27 AM)
High anchor is here for reference; not to reflect a practical purpose.


yes. But later people will say "ah yeah 48 kbit/s PS was clear worth than 128 MP3 " while there won't be ideal 128 but 133-135 kbit/s.
If VBR is better so let's control bitrate ( -V 5 ... -V 7). I.e. size of MP3 128 kbit/s should be 2.67 bigger than 48 kbit/s AAC+2. (128/48)

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NoXFeR
post Dec 15 2005, 17:40
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Gabriel: Is there any reason why streaming must be cbr?

As far as I see, it could be better to use VBR in some cases when streaming: Consider that your stream has an average bitrate of say 96kbps using VBR and you have a reasonably large buffer, would not that sound better than a 96kbps CBR stream? And if the buffer is large enough, it should not be a problem listening to this without chopping using a 128kbps conection.
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Shade[ST]
post Dec 15 2005, 17:45
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QUOTE (NoXFeR @ Dec 15 2005, 10:40 AM)
Gabriel: Is there any reason why streaming must be cbr?

As far as I see, it could be better to use VBR in some cases when streaming: Consider that your stream has an average bitrate of say 96kbps using VBR and you have a reasonably large buffer, would not that sound better than a 96kbps CBR stream? And if the buffer is large enough, it should not be a problem listening to this without chopping using a 128kbps conection.
*

The point of streaming is to listen without a download delay. For such a reason, you have to make sure your stream is constant, or the decoder will have to wait for some parts of it to arrive before being able to decode them. If you're using CBR, it's easy to plan how much of a buffer you'll need to have, to decode the file without skipping.
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NoXFeR
post Dec 15 2005, 17:57
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Well... Lowering the average bitrate of the VBR to 80kbps could still be better than the 96kbps CBR stream while requiring the same buffer. I understand that it is advantageous to have a easily predictable buffer size, though, even though I believe it could be calculated for VBR streams as well.
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Shade[ST]
post Dec 15 2005, 18:36
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QUOTE (NoXFeR @ Dec 15 2005, 10:57 AM)
Well... Lowering the average bitrate of the VBR to 80kbps could still be better than the 96kbps CBR stream while requiring the same buffer. I understand that it is advantageous to have a easily predictable buffer size, though, even though I believe it could be calculated for VBR streams as well.
*

we're talking about 48kps here. 56k modems can't have that sort of overhead.

Anything over 48kps will be skipping. And no, you can't predict the upcoming bitrate (otherwise you wouldn't need 2-pass modes...)
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NoXFeR
post Dec 15 2005, 18:51
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The bitrates were examples, modify them to the 48kbps-range for direct relevance. For instance, it is possible that 40kbps VBR sounds better than 48kbps CBR and at the same time they require the same buffer.

And if everything above 48kbps skips, a buffer isn't used. And as has been said here earlier, it isn't reasonable to expect 56kbps modems to play 48kbps streams reliably. It can be done, but it isn't the scenario one would expect. When I had dial-up, I tried several times and failed 90% of the time.

Lastly, of course you can predict the upcoming bitrate; using some statistics on similar music, artists and masterings should give a reasonable estimate. But that wasn't what was questioned: The question was whether one could easily predict what buffer size would be needed. One way to do this would be to take the song with the highest average bitrate until now and use a buffer size which allows this song to be played smoothly. This isn't a good way to do it, but it is a way to do it, and shows that it is possible.
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Shade[ST]
post Dec 15 2005, 20:06
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If a 40kbps VBR never goes above 48 kbps, it will never sound better than 48 kbps cbr..

the same applies to mp3s. preset insane is better than ape or aps because it's the upper limit of the bitrate of any mp3. (also the reason mp3s are the only format to have a cbr value at the top of their quality scale..)
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Ivan Dimkovic
post Dec 16 2005, 12:28
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One thing which worries me here - if the part of the this test's purpose would be to decide the best competitor for the 48 kbps multiformat test - then we also have a problem.

Vorbis will be tested in its quality-controlled mode, right?

So, we will compare best CBR encoder from the AAC test with the VBR encoder - which is quite unfair if I may say.
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IgorC
post Dec 16 2005, 14:01
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Coding Technologies Enhanced aacPlus (HE-AAC v2) ?

what codec should it be? From winamp, cd-da extractor or it will be provided from codingtechnologies?

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