Become a MacRumors Supporter for $25/year with no ads, private forums, and more!

Clarification of MPEG 4, AAC and Apple

MacRumors

macrumors bot
Original poster
Apr 12, 2001
51,581
13,195
Based on posts/responses on the forums, it appears there is still a significant amount of confusion regarding audio codecs and their implications.

For clarification purposes, "MP3" is officially known as MPEG-1 Layer 3. This audio codec provides the popular compression format that both iTunes and the iPod support.

Songs can be encoded at varying "bitrates". The most common bitrate for MP3 is probably "128kbps". This translates into 128 kilobits per second -- which means the format will use 128kilobits of data to encode one second of audio - no more, no less. Therefore, the final size of a file depends on both Bitrate and the Length of the Song.

Many users, however, prefer to utilize larger bitrates to achieve higher quality audio, but at the sacrifice of a larger final file size. Based on this popularly referenced c't magazine blinded study, it is commonly held that 256kbps MP3 are equivalent to original CD Audio:

In plain language, this means that our musically trained test listeners could reliably distinguish the poorer quality MP3s at 128 kbps quite accurately from either of the other higher-quality samples. But when deciding between 256 kbps encoded MP3s and the original CD, no difference could be determined, on average, for all the pieces. The testers took the 256 kbps samples for the CD just as often as they took the original CD samples themselves.

AAC/MPEG4

This page at Apple helps clarify some terms and definitions regarding the audio format: AAC. Advanced Audio Coding (AAC) is the audio codec for the standard known as MPEG-4. According to Apple's site, AAC provides advantages over MP3 -- but the most significant for end-users is the improved compression algorithm:

AAC compressed audio at 128 kbps (stereo) has been judged by expert listeners to be "indistinguishable" from the original uncompressed audio source.*

As a result, the advantage of AAC will be better quality audio at the same file sizes. Or, alternatively, equal or better quality at smaller sizes.

Some commonly asked questions:

Q: Is a 128kbps AAC/MPEG4 file smaller than a 128kbps MP3?
A: No. They are exactly the same size... but the AAC file should sound better. See above.

Q: Will there be a way to convert my MP3's to AAC files?
A: Converting directly from MP3 to AAC is not recommended (by this author). Going from a 128kbps MP3 to a 128kbps AAC file will provide no space spavings, and yet you will likely lose audio quality. (both are "lossy" file formats). Remember, you will never "regain" the quality lost when a song was encoded into MP3. The recommended course of action would be to re-rip the files from its original format (CD, for example).
 

Abstract

macrumors Penryn
Dec 27, 2002
24,561
403
Location Location Location
Bah, I hate it when they say that 256kbs is the same quality as an Audio CD. That's bull. I encode at 320 kbs and that sounds fine, but the bass is the weakest part of mp3 encoding. There are much better formats out there that are almost lossless quality.

Is this AAC going to be better than "almost lossless", because I sure can't see anything compressed as being completely lossless.
 
Comment

grapeice

macrumors newbie
Jul 23, 2002
7
0
Thanks!

Thank you for finally laying this all out. I know I heard this all, but I tend to forget, and I think others did too. It'll be interesting to see what Apple really goes with on this Music Subscription Service, if indeed that really rolls out too. :)
 
Comment

mattalici

macrumors member
Apr 18, 2003
33
0
LA
I love this!

I love that MacRumors takes the time to spell this stuff out for the little people. It took me like 5 years to figure out what mobo meant. (motherboard) I thought it was an insult.

Team MacRumors rules!
 
Comment

Steamboatwillie

macrumors regular
Mar 25, 2003
215
0
Memphis, TN
I don't agree 100% but mostly

As far as MP3s that is...

Encoding with different encoders, with different settings, yeilds different results. My favorite is LAME set with the --r3mix options. These files sound excellent and are close to most 128kbs file sizes. I encourage anyone interested to go to http://r3mix.net/ and read about it. My point is: not all MP3 files can be judged for quality based on just the bitrate. Also, unless the file sizes are reduced dramatically, I see no need for new codecs. I have an in dash MP3/CD player in my car and I'de like to get a few years out of it before I feel compelled to upgrade to whatever is new and better. I feel MP3 still has a lot of life left in it.
 
Comment

arn

macrumors god
Staff member
Apr 9, 2001
15,650
4,461
Originally posted by Abstract

Is this AAC going to be better than "almost lossless", because I sure can't see anything compressed as being completely lossless.

of course there are lossless compressions out there... there are a few audio ones (shorten, is on that comes to mind), along with all the usual compressions - zip, stuffit, gz, lzw.... those are all lossless.

AAC is lossy, of course... I don't know which formats you are talking about (almost lossless)

arn
 
Comment

Sheebahawk

macrumors member
Apr 2, 2003
63
0
Long Beach California
ipod and mpeg4

Can an ipod/itunes play mpeg4's as it is right now? if not I should probably wait until it does before buying one... I plan on using it in my car and I like my bass loud and clear...

would it be just as easy to start using mpeg4 as the standard audio format for apple's music solutions? like ripping cd's into mp4 on the next version of itunes? Calling it mp4's (unless mp4 is already taken by mpeg-1 layer 4 or something) would definately make the masses think that it is superiour to mp3's, and using it as the standard in apple's music service would just provide yet another advantage over gnuetella and any competing solutions.

Now I'm getting worried that i'll have to pay for the thousand songs I've already "borrowed", just to get the mpeg4 versions, so they sound better. I've already put all my cd's into storage/given them away/sold them after ripping them into mp3...

Mpeg-4's descriotion sounds good though, I hope apple pushes it as the new standard, as I've always worried about my mp3's sounding inferior to people who still use CD's.
 
Comment

evilbert420

macrumors member
Jul 22, 2002
71
0
MP3 to AAC

"Going from a 128kbps MP3 to a 128kbps AAC file will provide no space spavings, and yet you will likely lose audio quality."

Okay, but if all my MP3s are 320kbps, then that might be acceptable to convert to a 128kbps AAC, no?

I grimace to think about having to re-rip another 15gigs worth of albums. I assume it's only a matter of time before a conversion mechanism is available, unless AAC has some copy-protection embedded that would prohibit this.

When answering a question, it's okay to give your opinion... but you didn't answer the question of whether it can be done.
 
Comment

arn

macrumors god
Staff member
Apr 9, 2001
15,650
4,461
Re: MP3 to AAC

Originally posted by evilbert420
Okay, but if all my MP3s are 320kbps, then that might be acceptable to convert to a 128kbps AAC, no?

When answering a question, it's okay to give your opinion... but you didn't answer the question of whether it can be done.

The question becomes - why do you want to convert to AAC? Why do you want to convert your 320kbps MP3 to 128kpbs AAC?

It won't sound better... if anything, it'll sound worse.
It will take up less space... but drive space is cheap.

If you have an AAC-only playing device - that might be the most legitimate reason to do so.

As for "is it possible" - yes, it's possible. Right now, you'd have to convert to AIFF (noncompressed format first) and then convert that to AAC.

arn
 
Comment

ennerseed

macrumors regular
Jan 3, 2002
142
0
recmpress ect

just some personal thoughts...

I would keep you mp3s as they are.

i would re-rip your cds to aac... this time make sure it sounds good to you!

I have thousands ( 4221 ) of mp3s, I could re-rip but they are from vinyl and are a pain in the a** to record, much less tag properly. I have totally stoped recording my records till I find out what the final deal is with aac, iTunes, iPod.

As time went on I went from 128k to 320k and really wish this stuff came, would be coming, about faster.

Thanks for the info Arn
 
Comment

Tom800

macrumors member
Nov 29, 2002
72
0
Encoders

Is it possible that iTunes 4 will have the LAME encoder or a similarly top-quality encoder at its heart? I've heard the current iTunes encoder is decent and fast, but compromises on quality... Could there be an option to toggle between encoders?
 
Comment

arn

macrumors god
Staff member
Apr 9, 2001
15,650
4,461
Re: Encoders

Originally posted by Tom800
Is it possible that iTunes 4 will have the LAME encoder or a similarly top-quality encoder at its heart? I've heard the current iTunes encoder is decent and fast, but compromises on quality... Could there be an option to toggle between encoders?

you can use iTunes-Lame Encoder in the meanwhile

arn
 
Comment

redAPPLE

macrumors 68030
May 7, 2002
2,626
2
2 Much Infinite Loops
Originally posted by Abstract
Bah, I hate it when they say that 256kbs is the same quality as an Audio CD. That's bull. I encode at 320 kbs and that sounds fine, but the bass is the weakest part of mp3 encoding. There are much better formats out there that are almost lossless quality.

Is this AAC going to be better than "almost lossless", because I sure can't see anything compressed as being completely lossless.

i agree. compressing any file, would result to quality loss.
 
Comment

bignumbers

macrumors regular
May 9, 2002
206
0
AAC really better?

Has anyone independently done a real comparison of MP3 vs AAC? Apple claims AAC is better, but (as much as I do like Apple) they are of course biased towards their own products.

And you probably can't even do a direct comparison of MP3 vs AAC, because there are a multitude of encoders. If Apple is comparing a great AAC to their adequate (but not great) MP3, is that a valid comparison?

I agree that a conversion to something other than MP3 will be a tough sell. Many consumer CD players now play MP3 CD's. What will happen if you have a library of AAC's and want to make an MP3 CD? Could you? Would you need to convert everything? At what loss of time and quality?

And would there be a way to maintain mirror libraries of different formats? I'd like that now. I like high-quality MP3's for listening at home through good speakers. But when I'm mowing the lawn, do I really need 256K+? I have two MP3 players, a 5GB iPod and a 64MB Nomad IIMG; how about loading the Nomad with 64K music so I can store more than 45 minutes?

Oh, the confusion...
 
Comment

centauratlas

macrumors 65816
Jan 29, 2003
1,359
2,195
Florida
MP3 to ACC

>The question becomes - why do you want to convert to AAC? Why do you want to convert your 320kbps MP3 to 128kpbs AAC?<

For me, I would convert from 320kbps to some-kbps AAC for a couple of reasons:
1. If I can get the same quality at say 240kbps AAC as 320kbps MP3, then that gets more room on the iPod
2. It saves some room on the hard drive and gets the same quality.

Admittedly if Apple made a 50GB (or larger) iPod I would just record at the best quality bit-rate with the best quality encoder. But they don't yet do so.

Ideally what I would like it to have 7000 songs scanned in at the best quality available (320kbps MP3 when I did my scanning), and have iTunes have an option to send a 160 kbps (or something) version to my iPod. Then when i got a bigger iPod I would up the quality being synched to it.

Alternatively, I'd like something like the Rendezvous enabled iTunes with a tablet and speakers on the tablet. Then I'd have all my tunes available anywhere the tablet was in the house.

>It will take up less space... but drive space is cheap.

Except when you absolutely can NOT get more space on the iPod... ;-)
 
Comment

bikertwin

macrumors regular
Nov 6, 2002
198
0
This Old House
And remember that using VBR (variable bit rate), even iTunes' MP3 encoder does a good job at 160 kbps. Takes a little longer to encode, but it's worth it for the quality. MP3's tinny sound at 128 kbps drives me batty, but I still need to keep the file size down since my Sony Clie only holds a 128 MB memory stick.
 
Comment

mangoduck

macrumors regular
Oct 26, 2002
115
0
lost at sea
for those of you asking about mp3 to aac conversion, i really see no point.

lets say you have a jpeg file that you want to convert to some newer and more efficient jpeg compression algorithm. in photoshop, or graphics program of choice, open the file and save as / save for web and select jpeg. even though the new version of the format is better overall, your final product should look even worse than before. not only do you not magically regain image quality simply by opening the file in an image editor, but you also compress the artifacts that resulted from the FIRST compression.

i use this example because (i think, correct me if i'm wrong) mp3 audio compression uses the same principle as jpeg, and later, mpeg. i swear if you could listen to a jpeg, it would sound like an mp3.

so in short, you don't really gain anything from this conversion. stick with your existing mp3s, and just use aac for new rips from the source.
 
Comment

kwajo.com

macrumors 6502a
Jul 17, 2002
895
0
Bay of Fundy
Re: AAC really better?

Originally posted by bignumbers
Has anyone independently done a real comparison of MP3 vs AAC? Apple claims AAC is better, but (as much as I do like Apple) they are of course biased towards their own products.


I have ripped many of my most treasured CDs in mp4 through Quicktime and they are mixed in my iTunes library along with everything else (mp3s, wavs, aiffs). honestly, they do sound improved, and, just as with mp3, the higher the bitrate, the better. I have experimented with mp3-to-mp4 and it is not worth it, the quality does go down, so don't even think about it. the mp4s (despite what Apple says) do use more CPU, but that will probably improve as they become more integrated. don't listen to people who say that mp4s at half the bitrate of mp3 sound the same; that is garbage. 64 kbps mp4s do not sound the same as 128kbps mp3s, though they are miles ahead of their mp3 counterpart. I use either 160 or 192 as the bitrate for my mp4s, and for me tht yeilds good results (if I want full quality, I make the effort to go grab the CD off the shelf).

so in the end they do sound better, and once iTunes makes it easier to rip them and plays back a bit more smoothly, I would recommend re-ripping as many of your CDs as you have the patience to do.

p.s. It is true that telling people that you have a beatles collection ripped in 'mp4' sounds impressive, higher numbers make people believe it is better no matter what
 
Comment

impierced

macrumors 6502
Sep 30, 2002
273
0
Originally posted by Steamboatwillie
Try LAME --r3mix and save a bunch of disk space.

The "--r3mix" has been superseded by the "archive quality" "--alt-preset standard" for lame encoding.

--r3mix will be a bit smaller at good quality, but the --alt-preset standard will sound much better.

Do a blind test on your hi-fi system and I think you'll agree.
 
Comment

bennetsaysargh

macrumors 68020
Jan 20, 2003
2,367
0
New York
blind test

ok everyone. do a blind test and see for yourself which is the higher quality. a 192kbps mp3, or a 96 kbps mp4. i'm about to do mine now. i'll report back with my results later.
 
Comment

bennetsaysargh

macrumors 68020
Jan 20, 2003
2,367
0
New York
i just did a blind test, and mixed the 1st half and second half of a song. (1st half in mp3 and the 2nd in mp4. also done visa versa).
my results. they both sounded the exact same quality. the mp3 file was 5.5mb, while the mp4 was only 2.8mb. i'll stick with the mp4.
 
Comment

Abstract

macrumors Penryn
Dec 27, 2002
24,561
403
Location Location Location
That's not much of a blind test. :p


I wouldn't touch a thing. Its not as if this is an issue for me right now. It wouldn't be difficult to re-rip an album, but since I have everything at 320kbs, why would I want to switch over to mp4? To save HD space? I have plenty of space because i don't carry too many mp3's. When I don't like an mp3, or if I know I'll never listen to it ever again, I delete it. What would I do with 11 GB of mp3's, maybe show off my large collection? I have only what I know I may listen to. If you have enough HD space, then don't switch. Just because a new technology comes out, it doesn't mean that you need to make an issue out of nothing. If music quality wasn't a problem before, then don't switch for the point of switching. My music sounds great the way it is. ;)
 
Comment
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.