Skip to main content

Notice

Please note that most of the software linked on this forum is likely to be safe to use. If you are unsure, feel free to ask in the relevant topics, or send a private message to an administrator or moderator. To help curb the problems of false positives, or in the event that you do find actual malware, you can contribute through the article linked here.
Topic: Personal blind listening test – MultiCodec at ~192 VBR kbps (Read 10230 times) previous topic - next topic
0 Members and 2 Guests are viewing this topic.

Re: Personal blind listening test – MultiCodec at ~192 VBR kbps

Reply #75
@jaybeee
Also exhale xHE-AAC was the only encoder which was tested with CVBR mode (constrained VBR) while all other competitors were tested in their VBR modes.
exhale only supports CVBR.
I'm kinda late here, but I just wanted to ask - isn't Opus's "VBR" also kind of constrained? Opus provides no way to specify a target quality and let bitrate be whatever it ends up being, it can only target a specific bitrate (which, yes, it likes to overshoot, but the point still stands).

True VBR is when you throw stereo audio and mono audio at an encoder with the exact same settings and get close to double the bitrate for the former compared to the latter. LAME's -V, Vorbis's -q, etc. all behave this way. There's no way to do this with Opus.

Re: Personal blind listening test – MultiCodec at ~192 VBR kbps

Reply #76
Exhale's CVBR admits 1.25x variation of bitrate.
Opus VBR admits 2x ( for example target bitrate 128  kbps, peak 256 kbps) variation of bitrate and comparable to other VBR encoders. So, yes, it's VBR.

Every encoder has its own VBR implementation and adding it into some category doesn't reflect reality oftenly.
Whether it's  called "quality based" or "true" or  just "VBR" it's secondary. It's VBR.   


P.S. But if You wish,  Opus VBR implementation is quality based VBR.  It increases/decreases bitrate on type of signale (tonal, transients),  stereo (wide, narrow), complexity etc.... So  it's  "true" or "quality based"  if You wish to call it this way.
Opus has no fancy -V or -q mode instead Opus uses -b (bitrate) as targeting bitrate but it doesn't change the fact that it's VBR (outstanding and well tuned one)

P.S.2. It's simple to observe that only Opus was transparent on every killer sample. No way it would be possible if it hadn't well tuned VBR mode.  

Re: Personal blind listening test – MultiCodec at ~192 VBR kbps

Reply #77
Question, Is common for some to rate Lame MP3 at V2 as 4.90?.
Got locked out on a password i didn't remember. :/

Re: Personal blind listening test – MultiCodec at ~192 VBR kbps

Reply #78
P.S.2. It's simple to observe that only Opus was transparent on every killer sample. No way it would be possible if it hadn't well tuned VBR mode.  
It was not my intent to suggest that Opus's VBR "isn't VBR", nor that it isn't well tuned. Merely that it is - nevertheless - constrained, to some degree.

I mean, as long as the bitrate varies in any fashion, that's VBR - literally by definition. The bitrate is variable = variable bitrate = VBR. Whatever Exhale is doing is also VBR, because it produces files with variable bitrate.

I was not aware of the exact difference to which degree Exhale limits the variability of the bitrate compared to Opus, and I do agree that makes Exhale's VBR more constrained than Opus's. Nevertheless, the point remains that Opus has no way of encoding VBR without targetting a specific bitrate. I agree, this doesn't mean that Opus's VBR "isn't VBR". But it does mean that there's no way to encode with Opus while targetting a specific quality level rather than a specific bitrate. And "targetting a specific bitrate" is nothing other than constraining the bitrate to some degree. Yes, it's clearly incredibly well tuned - as obvious from the test results. If anything, the only thing I lament about this situation with Opus's VBR is that it could do even better than it already does, if it provided a way to encode VBR without having any specific target bitrate.

Re: Personal blind listening test – MultiCodec at ~192 VBR kbps

Reply #79
But it does mean that there's no way to encode with Opus while targetting a specific quality level rather than a specific bitrate. And "targetting a specific bitrate" is nothing other than constraining the bitrate to some degree.
https://wiki.xiph.org/OpusFAQ#How_is_the_bitrate_setting_used_in_VBR_mode.3F

Quote
How is the bitrate setting used in VBR mode?
Variable bitrate (VBR) mode allows the bitrate to automatically vary over time based on the audio being encoded, in order to achieve a consistent quality

The bitrate setting controls the desired quality, on a scale that is calibrated to closely approximate the average bitrate that would be obtained over a large and diverse collection of audio. The actual bitrate of any particular audio stream may be higher or lower than this average.

Hence, it's quality based.

Re: Personal blind listening test – MultiCodec at ~192 VBR kbps

Reply #80
But it does mean that there's no way to encode with Opus while targetting a specific quality level rather than a specific bitrate. And "targetting a specific bitrate" is nothing other than constraining the bitrate to some degree.
https://wiki.xiph.org/OpusFAQ#How_is_the_bitrate_setting_used_in_VBR_mode.3F

Quote
How is the bitrate setting used in VBR mode?
Variable bitrate (VBR) mode allows the bitrate to automatically vary over time based on the audio being encoded, in order to achieve a consistent quality

The bitrate setting controls the desired quality, on a scale that is calibrated to closely approximate the average bitrate that would be obtained over a large and diverse collection of audio. The actual bitrate of any particular audio stream may be higher or lower than this average.

Hence, it's quality based.
As much as I'd like it to be so just because they worded it that way, it actually isn't.

Both of these were encoded with bitrate set to 128 (same source audio):


Since setting the bitrate to 128 resulted in almost the exact same bitrate for both the stereo and the mono encode, the VBR is clearly bitrate based, not quality based.

Re: Personal blind listening test – MultiCodec at ~192 VBR kbps

Reply #81
As much as I'd like it to be so just because they worded it that way, it actually isn't.
Every article, documentation and site indicates Opus's VBR is quality based.  So this "they" is a little bit wider than You think.
I see only one person,You, who thinks than Opus's VBR is not "quality based".


Ask yourself a question if there is a real-case (reasonable ) implementation of VBR which is not quality based and post here example.

Another question will be  whether every real-case VBR encoder  is truely unrestricted and doesn't do some tricky bitrate restrictions based on how much bitrate was already used and so on. You will be surprised that some popular encoders (which have "q" setting) do that. "q" setting is not a panacea.  And here you have a very wide and quality based VBR encoder and complain that it's not quality based just because devs named and mapped "q"  setting with "b" setting.

More realistic two indicators of what someone can expect from encoder is wideness of variability  of VBR implementation and, of course, blind tests.  And Opus's VBR checks those boxes perfectly!.   "q" setting isn't an indicator of anything.

Since setting the bitrate to 128 resulted in almost the exact same bitrate for both the stereo and the mono encode
This has nothing to do with implementation of VBR. It's just a different mapping approach. You just ask an encoder to encode mono file  at that setting. And it does so.

Now if your create a stereo (not mono) file with exact the same L/R channels Opus will lower bitrate because of redundancy as a VBR encoder would do.

Re: Personal blind listening test – MultiCodec at ~192 VBR kbps

Reply #82
Opus brought this upon itself and it is indeed confusing.

If they said the bitrate was the stereo bitrate, and if you had mono or 5.1 it changed the target rate internally to match that quality, then it would make sense to treat the bitrate as a quality figure. But I believe (and I did not test myself sorry), if I have mono or 5.1 and I say 192 kbp, it will average around that 192 kbps in a large enough corpus.

In other words, one has to learn a rating for mono, stereo, 5.1, etc. 192 kbp is more than perfect for stereo, but definitely cannot be of the same quality for 5.1 or event 7.1

That is why it is hard for normal users. (Admittedly I care less as I only do stereo.)

Re: Personal blind listening test – MultiCodec at ~192 VBR kbps

Reply #83
Every article, documentation and site indicates Opus's VBR is quality based.  So this "they" is a little bit wider than You think.
I see only one person,You, who thinks than Opus's VBR is not "quality based".
It is "quality based" to the extent that the bitrate variation within the encode will, to a certain extent, vary depending on the signal complexity, in order to - again, to a certain extent - maintain a certain level of quality. (Note that this is the exact same sense in which pretty much any form of VBR - ABR and constrained VBR included - is "quality based".)

But it is not "quality based" in the sense that providing a target bitrate means just setting a quality level, as very clearly evidenced by the example I posted above: ~128 kbps VBR mono and ~128 kbps VBR stereo are certainly different quality, and yet encoding both with the same target bitrate setting produced them as such - at almost the exact same bitrate, rather than attempting to achieve the same level of quality.

This has nothing to do with implementation of VBR. It's just a different mapping approach.
These two sentences contradict each other. "Mapping approach" is a part of the implementation of VBR. If it has to do with "a different mapping approach", it also has to do with the implementation of the VBR.

You just ask an encoder to encode mono file  at that setting. And it does so.
Yes, that is literally what I am saying - I requested the VBR to achieve a bitrate of ~128 kbps, and it did that rather than achieving a certain level of quality. Therefore, the bitrate setting for the VBR determines a target bitrate, not a target quality. I don't understand why this is so complicated.

Re: Personal blind listening test – MultiCodec at ~192 VBR kbps

Reply #84
All right. I see, We were talking about two different things then. 

Development of Opus is finished nowadays. So don't expect -q setting for mono/stereo/5.1 quality-based setting.
The End.


Re: Personal blind listening test – MultiCodec at ~192 VBR kbps

Reply #85
It is quality based, but they just say find out your acceptable quality indicator (happens to be bit rate over a large average corpus) for mono, stereo, and for each multi-channel, and they will guarantee that we will keep it at that quality. Complicated music will still be above target and simple below. It is not ABR as there is no feedback loop to guarantee the average bitrate not to exceed the bitrate you gave.

IgorC beat me to it, but yeah.

To be honest a bit confusing, but not a show-stopper.

Re: Personal blind listening test – MultiCodec at ~192 VBR kbps

Reply #86
Opus brought this upon itself and it is indeed confusing.

If they said the bitrate was the stereo bitrate, and if you had mono or 5.1 it changed the target rate internally to match that quality, then it would make sense to treat the bitrate as a quality figure. But I believe (and I did not test myself sorry), if I have mono or 5.1 and I say 192 kbp, it will average around that 192 kbps in a large enough corpus.

In other words, one has to learn a rating for mono, stereo, 5.1, etc. 192 kbp is more than perfect for stereo, but definitely cannot be of the same quality for 5.1 or event 7.1

That is why it is hard for normal users. (Admittedly I care less as I only do stereo.)
A quick experiment with this disc image. A typical classical album.
https://www.discogs.com/Smetana-Wiener-Philharmoniker-James-Levine-The-Moldau/release/2148148
X

Re: Personal blind listening test – MultiCodec at ~192 VBR kbps

Reply #87
(Admittedly I care less as I only do stereo.)
I have a few albums by The Beatles and one or two others that are in mono. It's more annoying than anything else that I can't just actually set the quality level to what I want and forget it, but whenever I want to (re)encode I need to go "ok, so these albums are in mono, so I gotta lower the bitrate, then when I'm done with them raise it back up again...".

Re: Personal blind listening test – MultiCodec at ~192 VBR kbps

Reply #88
In my bitrate table (one file = one album ; ~255 albums on various genre), you can see some interesting variations for OPUS VBR:



(see the OPUS tab for these details)

For VBR 192 the lowest bitrate for an album is 151 kbps (128 kbps if I include movie soundtrack) and the highest is 235 kbps. The lowest value are usually mono CD (2 identical channels). It is true that some VBR codecs have stronger bitrate amplitude than OPUS but with ±20% on albums (it's probably higher on tracks and for sure much higher on shorter samples) it's clearly not "bitrate based" :)

Re: Personal blind listening test – MultiCodec at ~192 VBR kbps

Reply #89
The lowest value are usually mono CD (2 identical channels). It is true that some VBR codecs have stronger bitrate amplitude than OPUS but with ±20% on albums (it's probably higher on tracks and for sure much higher on shorter samples) it's clearly not "bitrate based" :)
That is with dual-channel mono though. Try single channel. :P

The reason it matters btw, if you check the data in bennetng's message, dual channel mono still incurs a not insignificant bitrate penalty compared to single channel for the same quality level. It is simply unnecessarily wasteful to encode mono in dual channel. But, if you tell Opus to encode single channel... then it targets the bitrate, not the quality level.

Re: Personal blind listening test – MultiCodec at ~192 VBR kbps

Reply #90
The reason it matters btw, if you check the data in bennetng's message, dual channel mono still incurs a not insignificant bitrate penalty compared to single channel for the same quality level. It is simply unnecessarily wasteful to encode mono in dual channel. But, if you tell Opus to encode single channel... then it targets the bitrate, not the quality level.
I think OPUS detects first the number of channels and then change internally some settings.
If you ask ~128 kbps VBR (-b 128) it will set the encoder differently according to the number of channels. That's why a 1.0 file has a totally different bitrate than a 2.0 file with two identical channels. The same apply for multichannel : -b128 for a 5.1 provides a much worse quality per channel than -b128 for 2.0. Both soundtrack will end with ~120…130 kbps but the stereo will have ~60kbps per channel and the 5.1 only ~20 kbps per channel.

In other words, -b128 doesn't have one single quality target: it has a significantly higher quality target for a mono (1.0) file than for a stereo (2.0) file, and even a much better quality target compared to a 5.1 file.
For the end user it's much easier to manage to get the desired bitrate with non-stereo file. But i's also confusing compared to other codecs.

Exemple: I like the quality of Apple's AAC at ~128 kbps (setting: -q 64). If I want this quality for a movie/concert in 5.1 I just have to keep -q64. But I don't have any idea of the final bitrate (probably ~3× higher because the number of channels is ×3¹).

With Opus, I'd like to keep the quality I'm used to get with -b 128 on CD for my 5.1 movie/concert. I don't have any idea of what setting I should use (probably something close to -b 384¹ because there are three time more channels to reproduce) but I'll know the approximate bitrate I'll get.

___
¹ In fact it should be inferior to this if the encoder is tuned for handling multichannel and encode efficiently channels similarities.

Re: Personal blind listening test – MultiCodec at ~192 VBR kbps

Reply #91
Analyzing a number of listening tests towards my dissertation a few years ago, I came up with a simple function which tells you quite accurately how to get roughly the same audio quality for different channel configurations. The following function gives you a weight w for each cc, where cc is the channel configuration written as a decimal number (1.0 for mono, 2.0 for stereo, 5.1 for surround, etc.):

w(cc) = cc^0.75

If you want to know the quality equivalent mono bit-rate of, e.g., 128 kbps stereo, you simply calculate 128 * w(1.0)/w(2.0) = 128 * (1.0/2.0)^0.75 = 76 kbps. That function also tells you that, with 5.1 surround, you need roughly twice the stereo bit-rate for the same level of audio quality. Based on my experience that's quite reasonable, at least with modern codecs like Opus, (x)HE-AAC, and MPEG-H Audio.

Chris
If I don't reply to your reply, it means I agree with you.

Re: Personal blind listening test – MultiCodec at ~192 VBR kbps

Reply #92
Analyzing a number of listening tests towards my dissertation a few years ago, I came up with a simple function which tells you quite accurately how to get roughly the same audio quality for different channel configurations. The following function gives you a weight w for each cc, where cc is the channel configuration written as a decimal number (1.0 for mono, 2.0 for stereo, 5.1 for surround, etc.):

w(cc) = cc^0.75

If you want to know the quality equivalent mono bit-rate of, e.g., 128 kbps stereo, you simply calculate 128 * w(1.0)/w(2.0) = 128 * (1.0/2.0)^0.75 = 76 kbps. That function also tells you that, with 5.1 surround, you need roughly twice the stereo bit-rate for the same level of audio quality. Based on my experience that's quite reasonable, at least with modern codecs like Opus, (x)HE-AAC, and MPEG-H Audio.

Chris
excellent! that should be in the wiki ;)

 
SimplePortal 1.0.0 RC1 © 2008-2021