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qaac cvbr 128 ends up in 82 kbps, for many different songs. Huh?

Hi,

Since the 2014 listening tests I am re-setting my compression standards.
Since Opus isn't an option for me because it's not supported on all my devices (yet), I went for (iTunes) qaac.

But these are the problems I have with it, from which the bottom one is my main concern here:
  • Option tvbr always hangs the job. (qaac 2.51). Any ideas? Or might it be that this takes longer than like 5 minutes?
  • When I use cvbr, it doesn't matter what target I set (cvbr 128, 200, even 500), it always end up in ±82kbps!?
    And this for several songs from different genres (blues, ambient, rock,..). Don't tell me the encoder decides by itself that this is enough kbps for so different songs!  Any suggestions?

Thank you.

P.S.: I know that 96 is almost transparent for qaac cvbr 96, but I still targetted higher just to be sure, even though my ears are not that good.  :-*

Re: qaac cvbr 128 ends up in 82 kbps, for many different songs. Huh?

Reply #1
It would help to know the exact command line string you are using.

Re: qaac cvbr 128 ends up in 82 kbps, for many different songs. Huh?

Reply #2
I'm using QAAC with LameXP and Apple Application Support extracted from latest QuickTime, and I've not faced any issues with CVBR/TVBR encodes as you have, so I suggest you give that a whirl. The GUI allows adjusting CVBR bitrate or TVBR quality (0-127), and you can pass custom command line options as well for controlling other (advanced) settings of QAAC. In fact there's a little blue help button beside the custom options field, clicking which shows all command options supported by the selected encoder straight from the official documentation!

And like Zarggg has suggested, it would help if you could provide the exact command string that you're passing.
Rap is NOT music

Re: qaac cvbr 128 ends up in 82 kbps, for many different songs. Huh?

Reply #3
In foobar2000 these parameters gave me cvbr with average bitrate of 128
Code: [Select]
-v128 -q2 -s -o %d -
-v = cvbr
-s = silent
-o = output
%d = ouput name, foobar variable

And here is a TVBR example that usually gives ~140kbps
Code: [Select]
-V73 -q2 -s -o %d -

Re: qaac cvbr 128 ends up in 82 kbps, for many different songs. Huh?

Reply #4
TVBR:
qaac.exe --raw --raw-rate $(SampleRate) --raw-channel $(Channels) --raw-format S$(SampleBits)L --he --tvbr 91 -q 2 --threading --title "$(Title)" --artist "$(Artist)" --album "$(Album)" --track "$(Track)" --date "$(Year)" --genre "$(Genre)" --comment "$(Comment)" - -o "$(DestFileAudio)"

I just noticed that he option is not available for tvbr. So that's probably why it crashes. WOuld be better to refuse and ouput an error, but well.
Pitty that my acount is locked on mediacoder forum AND that the posts I made from a fresh acount ("AccountLocked") don't get through the moderation, NOR does my e-mails on the designated "forum problem".  Someone shout those admins/moderators the forum is locked for many people!
I have so many feedbacks and bugs that I never could send to mediacoder.
Anyone still active @meiacoder, can forward my concerns?


CVBR:
qaac.exe --raw --raw-rate $(SampleRate) --raw-channel $(Channels) --raw-format S$(SampleBits)L --he --cvbr 128 -q 2 --threading - -o "$(DestFileAudio)"

This time "Idiotesque" from RAdiohead. Result: 84kbps
When I do it manually without HE option, the bitrate is close to target.
So my question becomes: Is it normal that HE option always ends up around 84kbps?

P.S. I'm not gonna switch software. I know how thát goes. Then you get problems there (at least I will, even if someone ele doesn't!) and I4ll end up in a PC full with software and full of help topics... :-(

Re: qaac cvbr 128 ends up in 82 kbps, for many different songs. Huh?

Reply #5
Quote
I just noticed that he option is not available for tvbr. So that's probably why it crashes. WOuld be better to refuse and ouput an error, but well.
If you run qaac directly from command prompt, you will see that qaac does exactly what you say (and it does not crash).

Quote
Is it normal that HE option always ends up around 84kbps?
For 44.1kHz stereo, highest bitrate option offered by Apple encoder for HE-AAC is 80kbps.
And It looks rather strange to me that you want 128kbps and HE-AAC. Do you know what HE-AAC is? It is basically a technology for efficient encoding in lower bitrate (~64kbps), where accuracy of upper half frequency components is sacrificed (it is replicated by a technology called SBR).
When you want 128kbps, just use LC.

Re: qaac cvbr 128 ends up in 82 kbps, for many different songs. Huh?

Reply #6
Quote
I just noticed that he option is not available for tvbr. So that's probably why it crashes. WOuld be better to refuse and ouput an error, but well.
If you run qaac directly from command prompt, you will see that qaac does exactly what you say (and it does not crash).
OK. Another Mediacoder bug?  May they realise it out of thin air. :-( (cfr. blue text above)
Quote
Is it normal that HE option always ends up around 84kbps?
For 44.1kHz stereo, highest bitrate option offered by Apple encoder for HE-AAC is 80kbps.
And It looks rather strange to me that you want 128kbps and HE-AAC. Do you know what HE-AAC is? It is basically a technology for efficient encoding in lower bitrate (~64kbps), where accuracy of upper half frequency components is sacrificed (it is replicated by a technology called SBR).
When you want 128kbps, just use LC.
Yeah, I know a bit. I just thought it would sacrifice relatively to the required setting or that even the low end part would be relative, but as you said it's the Apple encoder limit. I don't think you have to know HE-AAC to know that; you just have to know that apple limits it, not?  HE-AAC doesn't imply a specific maximum, does it?
Anyway, thanks! At least I know now. (I'd mark this topic "solved", but I can't find an original post edit option..:-/ ).
Also: Yes, meanwhile, I have considered not using HE. It does indeed feel rather silly at higher bitrates now.  :-)

Re: qaac cvbr 128 ends up in 82 kbps, for many different songs. Huh?

Reply #7
I think you still don't understand what SBR is and more importantly, how it is designed to work.

SBR is not a tool that is applied in addition to the other tools. It is a tool that first downsample the signal, sends it to the LC encoder, and then tries to compensate that downsampled signal with its "magic".  The downsampling target is not variable. It is fixed to half of the original sample rate, so for 44Khz you get a 22Khz AAC-LC + SBR on top to "simulate" a 44Khz file.

There is another case of which I don't remember the exact name which works with an upsampled signal. That case is probably more similar to what you were expecting. Winamp's AAC encoder used to have that option.

Re: qaac cvbr 128 ends up in 82 kbps, for many different songs. Huh?

Reply #8
Quote
Is it normal that HE option always ends up around 84kbps?
For 44.1kHz stereo, highest bitrate option offered by Apple encoder for HE-AAC is 80kbps.
And It looks rather strange to me that you want 128kbps and HE-AAC. Do you know what HE-AAC is? It is basically a technology for efficient encoding in lower bitrate (~64kbps), where accuracy of upper half frequency components is sacrificed (it is replicated by a technology called SBR).
When you want 128kbps, just use LC.
Yeah, I know a bit. I just thought it would sacrifice relatively to the required setting or that even the low end part would be relative, but as you said it's the Apple encoder limit. I don't think you have to know HE-AAC to know that; you just have to know that apple limits it, not?

You're telling it to encode the AAC part at half the sampling rate when you use HE.  It'll try to hit the target bitrate, but if you set the sampling rate low enough, and the bitrate high enough, it may not actually be able to do both.

Re: qaac cvbr 128 ends up in 82 kbps, for many different songs. Huh?

Reply #9
Thanks (to both) for the clarification. I did indeed not know about the fixed downsampling and thus it's inabililty to fake or reach higher bitrates.
(Though it's theoretically possible, I guess I have to stop presuming the maximum out of the magic. :-)  Luckily there are magicians like you that can correct me!  ;-) Tx again.)

 
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