[xnor]

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Okay, lot's of comments! Here's what I know (and as an audio engineer, look, we're not scientists - some of these arguments reach scientific levels to the point where it's no longer about what's important, which is perception).

Yes, perception is very important which is why we make listening tests. You need to eliminate (sub)conscious bias to get valid results. Any audio 'engineer' (sorry for the quotes, but engineer requires an academic degree over here) should know that.
 
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"24 bit to MP3 involves two conversions... 24 bit to 16 and uncompressed to compressed." - No, it depends on what bit resolution the encoder can handle. LAME 3.99 can encode an MP3 directly from a 24bit file (the LAME encoder is one of the most, if not the most popular encoder in the mastering community, likely what most of the MP3s out there have been encoded with).

Sure, some encoders indeed can handle above 16 bits, but the resulting MP3 isn't accurate anywhere close down to 24 bits. The only difference between a dithered 16-bit and 24-bit file encoded as MP3 is noise. Low level noise.
 
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Perhaps, the idea of keeping things CBR is (from other engineers who share this POV) to keep the encoder consistent; VBR will reduce the size of the file even more and when creating MP3s, my idea is to keep as much of the data as possible (a bit counterintuitive, I suppose). Pondering whether VBR sounds better than CBR is right up there with saying one fake Sugar brand is better than the next; they're still NOT real sugar

I don't understand 'keep the encoder consistent' but yeah your idea to keep as much data as possible is right. Since 320 CBR is the highest possible bitrate (higher than V0) you get the highest possible quality but also much bigger files, and: "but to date, no one has produced ABX test results demonstrating that perceived quality is ever better than the highest VBR profiles" (HA wiki).
 
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Trust me, the only ones obsessing over things like ABX testing aren't typically the people responsible for delivering this content to the masses (tends to be really analytical audiophiles that love to argue more than just chilling out and listening to the tunes!)

Sorry but I don't.
 
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"MP3 320 CBR doesn't filter out stuff above 16 kHz. As someone who masters audio you should know that." - I mentioned the LAME encoder, other encoders might not do it, but I mentioned that LAME is one of *the* most popular encoders, so likely some commercial tracks that people download have everything past 16kHz filtered out. Versions prior to 3.99 didn't, but I see a lot of MP3 files with missing frequencies past 16kHz; it's not that uncommon.

LAME also doesn't filter above 16 kHz with the highest settings. Not even with 192 CBR. If you get a LAME-encoded CBR file with everything above 16 kHz filtered out you got most likely a 128 kbit/s file - something I wouldn't even download for free.
 
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On paper, this is the truth. In the real world, I'll tell you what I did one time. I grabbed my wife's favorite CD and made a 320kbps MP3 version of it and I popped it in the car stereo on our way to run errands. After about 10 minutes, she said "Something's wrong with this CD, it sounds like it's going bad or something." My wife completely hates anything to do with analyzing audio and is simply someone who loves music without having any affection to anything technical (my favorite kind of person).

Nice story.
 
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Once you start talking science, it's possible to start believing things because someone can present a very articulate reason to the cause; I don't care for written theories of how a person perceives sound.

Yeah right, you start believing things for good reasons. Theories are not based on hot air but for example on listening tests.

 

[bigshot]

I've never seen a 24 bit MP3. I didn't even know such a thing was possible. Are the file sizes larger? I don't see how they could be with a defined kbps for the mp3 (256, 320 or whatever.) Can portable mp3 players handle 24 bit playback? I don't think AAC does that. I think iTunes downconverts 24 bit files to 16/44.1, then converts to AAC.

CBR uses the same number of bits to render dead silence as it does to render a complex orchestral string tone. VBR will only use as much as it needs to render the simple parts flawlessly, and it will give extra rendering quality to the complex parts. That means more efficient encoding because it's using the bandwidth efficiently. Sound quality isn't an issue with CBR or VBR. The only reason they offer you the option is in the early days, some primitive players couldn't play dynamically optimized bitrates. Everything can handle VBR now. There is absolutely no reason to use CBR any more. It isn't better quality, it's worse, because it's a file full of ballast.

By the way, I work in the business too, and I've done my own listening tests between 16 bit and 24 bit and uncompressed vs compressed. I found that at normal listening levels, there's no audible difference between 24 and 16, and AAC 256 VBR is audibly transparent to uncompressed. I'd encourage you to do the tests too. I didn't believe it until I did it myself either.

 

[xnor]

No there's nothing like a 24 bit MP3, but some encoders support 24-bit input. The output always is a 320 kbit/s (assuming 320 CBR) file. Afaik there's only one decoder (l3dec) that is accurate down to 24 bits assuming the input is a simple and very low-level signal (if it's masked by louder tones chances are low that the encoder will keep such low-level signals).
 
Regarding CBR vs. VBR: I cannot speak for AAC, but LAME's -V 0 switch limits the bitrate to the range 220 to 260 kbit/s. Of course, lots of silence will result in a waste of space with CBR, no question about that. Also, MP3 CBR does employ a mechanism called bit reservoir that allows the encoder to encode transient sounds better. Unused bits in one frame can be used in the following frame.

 

[bigshot]

Xnor, if I understand you correctly, it's just converting on the fly, and the only difference between encoding your mp3s directly from 24 bit and downconverting first is the quality of the dither? Is that correct? Because if so, I can't imagine there being any audible difference at all, because a good dither is totally transparent.

 

[xnor]

Atm I don't have time to do extensive ABX tests but DiffMaker shows a difference in correlation depth of 2 dB (btw, the correlation depth doesn't even reach 96 dB) and a simple null test shows a difference of less than 0.5 dB (peak, rms is ~0.2 dB) between the two.
 
I seriously doubt audible differences.

 

[HiFi1972]

Wow, for a bunch of proper engineers, some of you can be naaasty!! I was going to respond to some of the comments, but I'm suddenly not a credible source because I lack a proper degree
 
Oh well, I guess I'll just go and join the many other professionals who are working on audio who also lack proper degrees. Bye Scientists! Have "fun" in your research of fat-free, diet audio (had to use the quotes here too, ha!)

 

[bigshot]

No one questioned his qualifications that I saw. His profile says he's a sound tech. That's the guy who sets up the mixing stage for the sound mixer and runs the dubs afer the session. That's an audio engineer in my book.

 

[immtbiker]

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No offense, but everything you say in that paragraph is totally wrong, and I don't mean just your math.
Not 10%, 10X. High bitrate lossy has audibly identical soundstage and "air" (which are functions of the transducers, not the file format), the dynamics are identical and the response curve on the bass is the same.

No offense taken. I've always respected your opinion. When I re-read my post, I realized my math was in percentages of 100 and not 10's and I edited it before reading your post.
The rest, I have to take a serious look at.
 
A-

 

[bigshot]

It's not a direct A/B comparison, but it's easy to set up a quickie blind test in iTunes. Just rip the same CD three times... Once as Apple Lossless, once as a 320 MP3 and once as AAC 256. Put it on random shuffle and turn off your monitor. When each song is about to end, try to guess which file format it is and turn on the monitor, check the file type column and see if you're right. Good luck! Much harder than many people think.

 

[wberghofer]

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[…] Much harder than many people think.

 
You know, we had a → very similar discussion a few weeks ago, and I’m aware that we share quite contrary opinions about the never-ending story “Lossless vs. lossy file formats”.
 
My assertion has no “scientific” background, I can’t offer any statistical data and I don’t operate a perfectly calibrated sound lab suitable for ABX testing, but I certainly do know that after listening for approximately one hour to lossy compressed music my audio perception feels somehow exhausted or spent. However, even after some hours listening to lossless music, this condition has not occured.
 
It does not matter if I use my KRK active monitors or my Beyerdynamic T1 headphones for listening. I can assure you that this is not caused by some placebo effect. I know that this effect also occurs in other people who are not interested in analytical comparisons of playback quality, but simply prefer to enjoy the music instead.
 
Werner.

 

[Clarkmc2]

I am terrible at critical listening because I can't stay focused on the audio quality. Almost immediately I focus on the music and forget to pay attention to the sound quality.

It is not that I am adverse to experiment, but rather a function of how completely I love music. As I have explained, I can't multitask listening to music. I am not a natural at mixing the sacred and the profane, I suppose. I prefer to think of it as prioritizing my time on Earth.

 

[proton007]

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I am terrible at critical listening because I can't stay focused on the audio quality. Almost immediately I focus on the music and forget to pay attention to the sound quality.
It is not that I am adverse to experiment, but rather a function of how completely I love music. As I have explained, I can't multitask listening to music. I am not a natural at mixing the sacred and the profane, I suppose. I prefer to think of it as prioritizing my time on Earth.

 
Agree.
If the music is interesting, I don't mind youtube videos, as long as they are not terribly compressed.

 

[bigshot]

I certainly do know that after listening for approximately one hour to lossy compressed music my audio perception feels somehow exhausted or spent. However, even after some hours listening to lossless music, this condition has not occured..

Classic expectation bias. I'm sure you listen to low resolution sound on television sets or car radios all the time without becoming exhausted. When you put on a DVD or bluray, there's a good chance you're listening o lossy audio without even knowing it. Cable TV uses compressed audio. It's all around you, not just in iTunes.

Sound quality isn't a magical thing that makes you happy or sad or energized or exhausted. Music can do that, but not just sound quality... Not unless there is a huge headache inducing response spike in an inaudible frequency, and lossy audio just doesn't have that.

It is very easy to find out what the difference is between lossy and lossness. Even if you're sloppy about setting up your test, it's still easy to discover that they are very very VERY close. The fact is, it's so close, the only way to know for sure is to set up a line level matched switchable A/B comparison... And even then, it's so close it's impossible to tell... Because there is no audible difference.

It's easy to tell that lossy sounds as good as lossless. Any fair comparison will show you that. It's a lot of work to tell for sure whether they're audibly identical or not. Most people don't want to spend the time. They just say, "I'll play it safe and just encode lossless, just in case." That's fair if you really don't care. But that doesn't change the outcome of the tests done by those who *have* taken the time to do the test.

I'm not being stubborn or insistent. I've done the test. I know. No one can convince me otherwise because I experienced it for myself. That isn't the case with thse who rely on "feelings" and "impressions". They don't know, they just feel the need to justify their decision to not care and play it safe. That's being stubborn and insistent.

There is a difference between lossy and lossless... file size. That's enough to create an expectation bias in people who worry about OCD stuff. Normal folks with human ears who take the time to find out, just *know*.

 

[bigshot]

I am terrible at critical listening because I can't stay focused on the audio quality. Almost immediately I focus on the music and forget to pay attention to the sound quality.

If you have speakers and want to get the most out of them, you might want to hire someone to calibrate your response then. Because equalizing requires a LOT of very precise listening and analysis. Unfortunately, it isn't something that you can just let slide. It's the single most important thing you can do to achieve good sound.

But if average sound is fine, just buying a couple of inexpensive bookshelf speakers and using the bass and treble is fine. I wouldn't spend more than $700 on a stereo without equalizing though. It's a waste of money to buy good speakers and play them out of calibration.

 

[wberghofer]

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Classic expectation bias. […]

 
Classic expectation bias cannot be the case when people are not aware about the audio source or the file type. Please stop telling me and others what we feel, I’ve been listening long enough to both lossy and lossless music, and I do know how I feel after a while.
 
You also can’t compare the attention level paid to music playback or the soundtrack of TV and movies. When watching movies or TV, the moving image is the dominating part of the experience, but not the sound track.
 
When reading your posts, I often get the impression that your main goal was that your audio library fits into 2 TB of storage. If you’re happy with your incredibly extensive audio library ripped to AAC 256 VBR, then so be it. I’m happy when listening to my selected library in ALAC format, and fitting its size to a given storage size was not my primary goal; it was quality instead.
 
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[…] I know. No one can convince me otherwise because I experienced it for myself […]

 

That’s wonderful self-explanatory, isn’t it?
 
Werner.