Digital Audio Formats: A Guide

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Teqnilogik

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Today there are a variety of different digital audio formats to choose from. Enough to cause confusion amongst new users who wish to convert their CD library into digital form for easy listening on their computers or portable audio device such as the iPod. This guide is designed to help newer users on deciding on a format to rip his or her music to.

The first thing you should consider is what you need from an audio format. Compatibility? Quality? Playable on your portable device? There is no right or wrong answer on which format you should use. It's a personal choice and it depends on your needs.

There are two types of audio formats: lossy and lossless. Lossy formats throw out audio information when encoding to lower the file size of the song so no lossy format is technically CD quality. However, perceivable quality is more important and lossy formats can provide audio that is indistinguishable from the original CD. Lossless formats work like Zip files. It compresses your audio as much as it can without throwing out any audio information. When the losslessly compressed file is decompressed it will have the same quality it had before it was compressed. In other words, lossless formats retain the CD quality audio on your CDs. There is no quality loss.

The bit rate of a file is the data rate that the audio is compressed at. There is no clear answer to which is best, it all depends on your hearing. Do some comparison tests between the CD quality audio and encoded files at various bit rates and determine which sounds best to you. Bit rates are used in the following ways:

CBR (constant bit rate) - The file is encoded using the same bit rate throughout the entire file.
VBR (variable bit rate) - The bit rate changes throughout the file according to the complexity of the music to offer the best quality.
ABR (average bit rate) - This is a simple VBR mode where the bit rate flucuates through out the song and averages out to be a certain bit rate.

Now let's start reviewing the various audio formats.

LOSSY FORMATS:

MP3

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This is by far the most popular audio format in use today. It was the first lossy compression codec which means it is also the oldest lossy compression format. MP3 can achieve transparent, or indistinguishable from CD, quality at around 192kbps-256kbps to most people on most samples. The LAME encoder is highly recommended when encoding MP3s by the folks at Hydrogenaudio.org. It is the highest quality MP3 encoder available. When using the LAME encoder, using one of the Q settings with the --vbr-new command is recommended. They provide different bit rates depending on the complexity of the music and the quality level that was chosen. For example, you can choose from Q 0-9 and each will give you different bit rates. Q 0 will give you the highest bit rate and Q 9 will give you the lowest bit rate. See the Recommended Settings link below for more info. If you are concerned about compatibility with software and portable audio players then this is the format to use.

Recommended encoders
Recommended settings

AAC
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AAC, or Advanced Audio Coding, is a relatively new format. AAC has been made popular by Apple because of its integration into Apple's iTunes music software and its iPod portable audio player. At any bit rate, AAC should sound better than MP3. Likewise, a 128 kbps AAC file should sound better than a 128 kbps MP3 file. However, LAME encoded MP3 files encoded at 128 kbps are statistically tied to the quality of iTunes AAC at 128 kbps according to this listening test. AAC is gaining popularity and so it is becoming compatible with more media players. The Apple iPod and Microsoft Zune are the two major portable audio devices to support AAC. Note that AAC is not owned by Apple. It is defined in the MPEG-4 standard which means any portable audio device has the capability to add support for the format. The iTunes Music Store uses AAC at 128kbps. However, the iTunes Music Store wraps the FairPlay DRM protection around the MPEG-4 AAC files it sells. FairPlay is proprietary to Apple and currently Apple does not license it to other companies so the iPod remains the only player to be able to play files bought from the iTunes Music Store. Any music ripped to AAC in iTunes does not have any DRM protection attached to it. iTunes now has two free AAC encoder competitors. You have FAAC which is an open source AAC encoder but its quality is not up to par with iTunes or the next free offering. Nero Digital is the second free AAC encoder that is now available free of charge.

Recommended encoder: iTunes AAC encoder.

Other encoders: FAAC, Nero Digital, Compaact

Recommended settings: 128 kbps - 192 kbps depending on which sounds best to your ears.

Ogg Vorbis - http://www.vorbis.com
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This is an open-source and patent free audio format. MP3 and AAC are patented formats that must be licensed in order to be used. The advantage to Ogg Vorbis is that it is free to use without any restrictions. Ogg Vorbis should sound better than MP3 at the same bit rate. Ogg Vorbis has a few portable audio players that play it and media player software is beginning to support it more. A lot of game developers are using the format to avoid paying licensing fees. Ogg Vorbis is not supported by the iPod. iTunes can play Ogg Vorbis thanks to a QuickTime plugin available here, http://qtcomponents.sourceforge.net.

Recommended encoders and settings

MusePack - http://www.musepack.net
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MusePack is considered the best lossy audio format today. It excels at bitrates above 160 kbps and can achieve transparency in the 160 - 200 kbps range to most people on most samples. However, MusePack doesn't have much support. No portable audio device yet plays this format and only a handful of media players support playback of MusePack natively. Most media players require a plug-in to support MusePack. iTunes does not support this format and neither does the iPod.

Recommended encoders and settings

WMA
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WMA is Microsoft's answer to MP3. Exclusive to the Windows platform, WMA offers better sounding files at lower bit rates but currently WMA is not the best audio format. Better tuned MP3 encoders, AAC, Ogg Vorbis, and MusePack all beat WMA's quality at 128kbps and above. This format is not supported by the iPod but iTunes does offer a feature to convert WMA files to AAC/MP3 files for playback on the iPod.

LOSSLESS FORMATS:

FLAC
- http://flac.sourceforge.net
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FLAC stands for Free Lossless Audio Codec which is exactly what it is. It is non-patented and open-source. It supports multiple computing platforms and is considered the best lossless codec available by many. Encoding and decoding are both fast, compression is good, and seeking throughout a file is also fast. Currently, iTunes and iPod do not support FLAC.

Apple Lossless Audio Codec
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This is a new lossless codec developed by Apple for iTunes and iPod. Apple's Lossless Audio Codec's compression is about equivalent to FLAC's using the highest compression setting in FLAC. Apple Lossless will play in iTunes and iPod (with a firmware update). As this is a new codec support is low at the moment. Currently, only iTunes will play it but there has been plugins popping up for Winamp and I imagine more will surface in the future for other media players.

Monkey's Audio - http://www.monkeysaudio.com
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Monkey's Audio is another lossless compression format. It generally compresses better than FLAC using the highest setting, however, having the best compression isn't the best thing when talking about a lossless codec. Monkey's Audio is a Windows-only format and encoding, decoding, and seeking is slower than FLAC.


I wrote this because of the many posts made about which format to choose so I figured this forum needed a sticky about the topic. Feel free to let me know of any inaccurate information in the above and I will correct it accordingly.


Related Links:

- Results of Multiformat at 128kbit/s Listening Test
- Results of AAC at 128kbit/s v2 Listening Test


Updates:

{Edit by AndyH: Added some formatting commands for easier reading; Made thread "sticky"}

09/10/2004 - added recommended encoder and settings links to lossy formats section.
09/16/2004 - updated AAC section, fixed MP3 encoders link.
10/20/2004 - updated MP3, AAC, MusePack sections and added Related Links section.
04/13/2005 - updated various sections; rephrased some statements.
12/12/2006 - updated MP3 and AAC sections.
 
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stasyna

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192 and 256 kbps
Concerning --alt-preset standard, it ranges from 128 kbps to 320 kbps, and is around ~190-210kbps

also, if someone wants best possible VBR quality (and keeping ease of use in mind) --alt-preset extreme is an excellent option.

note the above concerns mp3 only
 
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Galley

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RealPlayer 10 also has a lossless format, RealAudio 10 Lossless. Although RP10 rips CDs as .m4a AAC files be default, it also has RealAudio 10, which is AAC at 128Kbps or greater.
 

slodojo

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I thought it might also be useful to add that, according to the forums at hydrogenaudio.org, the recommended lame version is 3.90.3 as of 9/9/04. 3.96.1 seems to be just as good, according to the preliminary listening tests on those forums, and it encodes much faster, but because there haven't been any improvements over 3.90.3, it is not yet considered the recommended version of lame.

-slo
 

Teqnilogik

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LAME 3.90.3 is the Hydrogenaudio recommended version only because it has been the most widely tested. They know that 3.90.3 is transparent on the most samples. The reason 3.96.1 is not recommended is because it hasn't been as widely tested. I highly doubt you will ever see another version of LAME recommended by them until LAME reaches 4.0. The 4.0 mark might inspire mass testing to make it the recommended version. But in my experiences, 3.96.1 performs just as well as 3.90.3 and often gives lower bit rates on files using --alt-preset standard. Plus it is faster.
 

hans-jürgen

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Hi Teqnilogik, good introduction that you wrote here. :) Of course I have some additional remarks:

* Link to recommended MP3 encoders is not there.
* There are more AAC codecs than iTunes' which is a different situation to MP3 or Ogg Vorbis or Musepack, so it should be mentioned in my opinion.
* I understand that this forum features the iPod, but it's a myth that it is the only AAC portable worth mentioning. The Philips Expanium is much older, the DivaGEM much smaller, and with the new mobile phone generation (Nokia, Sony Ericsson et al) the existing AAC hardware support right now is in fact much wider than your guide says. Even OggPlay, a SymbianOS based software player for these phones, has added MP4 support some days ago (sic!). ;) And AAC/MP4 multichannel support on DVD players is just around the corner.
 

saratoga

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AAC, or Advanced Audio Coding, is a relatively new format. AAC has been made popular by Apple because of its integration into Apple's iTunes music software and its iPod portable audio player. AAC has 30% more encoding power than MP3. At any bit rate, AAC will sound better. A 128 kbps AAC file sounds closer to CD quality than a 128 kbps MP3 file. If you own an iPod this is the format to use. It is gaining popularity and so it is becoming compatible with more media players but currently the iPod is the only major portable audio device that can playback MPEG-4 AAC.
Actually the 30% figure isn't very accurate. At low bitrates its actually very high. Probably closer to 90 or 100% at 32-48kbps.

And by the time you get up to 128k, theres practically no difference. The latest listening tests at 128k actually show iTunes AAC and LAME MP3 statistically tied:

http://www.rjamorim.com/test/multiformat128/results.html

(note the error bars)
 

Teqnilogik

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True, AAC at the moment is statistically tied to LAME MP3. Note that technically, by a small margin, AAC did do better in the test than MP3. However, if you compared AAC to the Fraunhofer MP3 encoder the results would be different. LAME represents the best that the MP3 codec has to offer. It has been very finely tuned to be the best. Unfortunately, LAME isn't the dominate MP3 codec in use today in the majority of music ripping applications. iTunes, Windows Media Player, MusicMatch Jukebox, and others all use Fraunhofer's MP3 encoder. Rip an MP3 with one of those programs and you'll notice a difference between the 128 AAC and 128 MP3. Though, personally I can tell a difference between a 128 AAC and 128 LAME MP3 - there are less artifacts in the AAC.

But generally, the information I've found state that AAC is roughly 30% more efficient than MP3 at encoding. It is also a totally different format as well so artifacts will sound different and can be less frequent as well so that will be a factor on audio quality as well.

Thanks for your reply. I plan on updating my article soon to add more information and explain some of the formats a little bit better.
 
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saratoga

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True, AAC at the moment is statistically tied to LAME MP3. Note that technically, by a small margin, AAC did do better in the test than MP3.
Well its within the error bars, so really it didn't do better any objective sense of the word, and certainly not 30% better which is really what I objected to.

However, if you compared AAC to the Fraunhofer MP3 encoder the results would be different. LAME represents the best that the MP3 codec has to offer. It has been very finely tuned to be the best. Unfortunately, LAME isn't the dominate MP3 codec in use today in the majority of music ripping applications.
Why would you do that though? If ones selection criteria is not quality, then why would they be compareing the quality of codecs? Obviously they would not. If one is interested in quality, then only the best and not the second or third or worst quality possible with a codec is of interest.

I'm also curious why you think fhg is the mainstream codec. This is debateable and there is little evidence.

iTunes, Windows Media Player, MusicMatch Jukebox, and others all use Fraunhofer's MP3 encoder. Rip an MP3 with one of those programs and you'll notice a difference between the 128 AAC and 128 MP3.
Acutally iTunes does not use fhg. It uses a much older and much worse encoder. I certainly hope you aren't using iTunes as your MP3 encoder in any of your tests.

Though, personally I can tell a difference between a 128 AAC and 128 LAME MP3 - there are less artifacts in the AAC.
Such generalizations are not relevent. What settings did you use? What versions? What samples? What equipment? What testing procedure? The list goes on. Its best to just stick with objective facts when discusseing audio, otherwise one gets sucked into a mess of wishy-washy terms and feelings that don't have a concrete meaning.

But generally, the information I've found state that AAC is roughly 30% more efficient than MP3 at encoding. It is also a totally different format as well so artifacts will sound different and can be less frequent as well so that will be a factor on audio quality as well.
The literature is obviously wrong, and you agree with me on this point, so why propigate the error? Better to spread information IMO.

Also, AAC and MP3 (as well as WMA and WMA Pro!) are very similar codecs compared to the rest of whats out there. Thats why they generally produce the same artifacts on the same samples. Ogg and musepack are very different in comparison.
 

Teqnilogik

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True Saratoga, you brought up some good points. I agree that the conclusions I reached could be wrong in most areas. In my test I compared iTunes AAC to LAME MP3 with a set of decent headphones. I know LAME is the best MP3 encoder out there so I use when I encode to MP3. 128 AAC just happens to suit me. But yeah, this is a very subjective area where a million things can come up into the debate about which format is better. Really it's personal preference and what one thinks sounds better and gives them reasonable file sizes. But good listening tests due help in choosing a quality codec.

By the way, what MP3 encoder does iTunes use? Any site with documention on which MP3 encoder it uses? It said, "MPEG-1 Layer 3 audio coding technology licensed from Fraunhofer ISS and THOMSON multimedia," in iTunes' About dialog box so I assumed they used Fraunhofer's encoder.

Thanks for your reply Saratoga, it was much appreciated. Your input was informative.
 
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mlts22

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From what people have said, I'm pretty sure they use the Fraunhofer's encoder. (The MP3 version, not the MP3Pro version which is compatible with MP3, but allows for better low end, though I have not messed around with the MP3Pro format.)
 

dragfree

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T-logik--This is an excellent introduction to audio formats, but there are a few opinions presented as if they are facts.

"MP3 can achieve transparent, or indistinguishable from CD, quality at around 192kbps-256kbps."

Even at 320kbps MP3 is distinguishable from CD with good source material and playback equipment, though less so with typical pop recordings played through an iPod or other DAP with standard earbuds.

"When using the LAME encoder, the --alt-preset standard setting is recommended. It provides bit rates usually between 192 and 256 kbps depending on the complexity of the music and provides transparent quality on most music."

Recommended by whom? I use LAME alt-preset insane 320kbps. It sounds better than alt-preset extreme, which in turn is clearly superior to alt-preset standand. The 320kbps setting comes closest to "transparency."

"AAC has 30% more encoding power than MP3."

30%? This figure is meaningless, yet presented as if it were a fact based on some objectively measurable criterion.

"At any bit rate, AAC will sound better than MP3."

I cannot agree completely. I rather like AAC at 256 and 320. At these bit rates it sounds pretty darned good to me. But so do LAME MP3s. And they all sound similar enough to one another and to the original digital CD files that I would have a difficult time choosing one as superior to another.

"a 128 kbps AAC file sounds closer to CD quality than a 128 kbps MP3 file."

I certainly agree that 128kbps AAC files sound better than 128kbps MP3s. AAC was developed to provide more acceptable quality than MP3s at the low bitrates suitable for streaming transmission over the web. The developers claim that AAC@128 sounds as good as MP3@160. But not even they claim that it's very close to CD quality.

"Ogg Vorbis provides better quality than MP3 and is about equivalent to AAC in terms of quality at the moment."

The listening tests you cite rate Ogg superior to AAC--and that's at 128kbps, the rate which AAC is engineered for, whereas Ogg is designed for high quality instead of high compression and really shines at high bit rates. Interesting that you cite the statistically insignificant difference between LAME and AAC as evidence that AAC is superior, but disregard the statistically significant difference confirming Ogg's superiority to AAC.

For a pretty good basic introduction to lossy compression and competing formats, I recommend this Wikipedia article: http://en.wikipedia.org/wiki/Lossy_data_compression

For an interesting comparison of MP3 and AAC, I recommend this paper on the subject by a Fraunhofer engineer (one of the developers of both): http://www.aes.org/publications/downloadDocument.cfm?accessID=14703162000122117
 
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Teqnilogik

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Thanks for pointing some things out, however, without starting a debate, I'd like to ask you a few questions.

You say Preset Insane sounds better than Preset Extreme. Did you do an ABX listening test to determine this? I'm asking because if you didn't, the placebo effect could be in play here.

And I would say that not ALL lossy codecs are easily picked out at high enough bit rates. If you take say, MusePack, and encode a track at the Braindead setting, I would bet that the majority of the people ABXing that track would not be able to tell a difference between it and the original CD quality.

I did make some modifications to my guide, thanks for pointing out potential areas where people may disagree.
 

dragfree

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Hi, TL. I commend you for the modifications and for your humility in making them. And I apologize for what in retrospect seems an overly critical tone. Yes, I've done ABX testing (using Foobar) of LAME MP3s and AAC at different bitrates, and using good classical & jazz recordings which are generally more revealing than typical pop fare. I would agree that LAME extreme sounds very close to LAME insane, yet in critical passages I can distinguish between them enough of the time (around 7 out of 10) to back up my general impressions. Note they are certainly much closer than AAC at 128 and 256, between which I scored 100% accuracy without effort the only time I tried. And my testing between LAME and AAC at 320--as with AAC at 256 and 320--was inconclusive, which isn't surprising since both sound very similar to CD to me as well, at least when played back through my PC.

If I were extremely concerned about storage space, I'm sure I could get along happily with LAME extreme or AAC@256 strictly for iPod playback, but the extra 20 or 25% storage space the larger files require strikes me as cheap insurance against feeling the need to re-rip in the future, as does using the LAME MP3 format instead of AAC. As for MusePack, I'll take your word for it, especially since I have a hard enough time distinguishing between LAME and CD as it is! :)
 

fallenipod

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ipod 6g needs to be way bigger memory and better battery so we can use lossless format. i listened to it and it sounds good and would really sound good wired to a car. i want that quality but it was 1064kbps lol.
 
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