Introduction
Lossless v Lossy
Lossless
Lossy

Introduction

Confused by the different audio file formats out there? Then this is the page for you!

Here, John Dalling attempts to give a simple rundown of the most common audio file formats available, and their uses.

No single file format is perfect for everybody, which is why so many different ones exist. The best thing to do is to try a few formats out, and discover their advantages and disadvantages for yourself. Someone with super hearing will probably prefer a lossless format, or a lossy format with limited compression. Someone with poor hearing and a small hard disk, on the other hand, will probably prefer a lossy format with greater compression to reduce the file size as much as possible.

Lossless v Lossy

There are two distinct types of audio file format. Lossless file formats retain every single piece of audio information, so when you play it back it will sound exactly the same as when it was created. This means two things: firstly, that there is no distinction in sound quality between different types of lossless sound file; secondly, that files stored in lossless file formats will be bigger than those stored in lossy file formats. However, if you want to create a perfect copy of a music file; for example if you are a music producer looking to archive your tracks; using a lossless file format is the best way to go. The common WAV (wave) file format, used by most audio editors, is a lossless file format.

Lossy audio file formats are designed to reduce the size of the file as much as possible, and they do this by getting rid of some of the data in the original piece of audio. Usually this is done to those parts of the track which are the least audible to the human ear. The MP3 file format is a lossy file format.

Lossless File Formats

WAV | FLAC | Monkey's Audio (APE) | True Audio (TTA)

Lossy File Formats

MP3 | AAC | OGG (Ogg Vorbis) | RealAudio | WMA

WAV File Format

WAV, or wave, was the original sound file format for the PC and has been with us for some time. WAV is a lossless format, so sound quality isn't an issue, but WAV files do tend to be on the large side. The WAV file does have one major advantage, though, in that it is the bog standard file format for audio on the PC. These days, WAV files are primarily used for audio manipulation, and it is often the standard employed by audio editors, sequencers and the like. When it comes to storing full tracks, however, the WAV file is a bit long in the tooth, and there are other, more efficient lossless formats. Despite this, because WAV files do not employ the same heavy compression as other lossless formats, they are quick to play as they don't require decoding.

FLAC File Format

FLAC, or Free Lossless Audio Codec, is a lossless, compressed audio file format. FLAC has become a popular lossless format due to its availability - its source code is in the public domain, which means that anybody can build a FLAC player. FLAC files aren't as efficiently compressed as some others, e.g. Monkeys Audio, but their decoding speed is relatively quick. FLAC files also support tagging within the file itself, rather like ID3 tags for MP3. A disadvantage for Mac users is that the format isn't compatible with OS9. FLAC files can support streaming audio (audio which can be played as it is downloading).

Monkey's Audio (APE) Format

Monkey's Audio is a lossless, compressed audio file format. A Monkey's Audio file can be up to 60% smaller than its WAV counterpart, and as it is a lossless file format, sound exactly the same. Monkey's Audio files have the .APE extension, and also support in-file tagging. One problem at the moment with this format is support - the files are only handled by audio players which have the appropriate plug-in. Another drawback is that, compared to other lossless formats, APE files take longer to decompress ready to play. Great file format if you're looking to store lossless files and save space; not so good if you want your audio files to be played back on lots of different players.

True Audio (TTA) Format

True Audio is another lossless, compressed audio format. The compression can be from about 30% up to 70% of the original size of the file. TTA files can store ID3 tags, like MP3 files. The code is also open source. As with Monkey's Audio, support among major players does not usually come as standard, but plug-ins are available for Winamp, Quintessential Player and more; a standalone producer application is also available called Tau Producer.

Examples from True Audio's website claim favourable comparison to other lossless formats, with a good balance between encoding time and file size.

MP3 - MPEG-1 Audio Layer III

MP3 is probably the most well known music file format out there, and enjoys wide support among software music players, and even modern home stereos and car systems. MP3 is also one of the oldest compressed music file formats, which also means its one of the least efficient. The difference in size between an uncompressed WAV file and an MP3 file is such, however, that despite MP3 not having the best compression codec or sound quality available, it has become the standard file format for today's music listener.

The quality of MP3 files can vary vastly according to the encoder used to create the file, and the bitrate (the number of binary digits streamed per second) of the file is encoded. The two bitrates most widely used are 128kbps and 192kbps. Tests have shown that the majority of people can distinguish between a CD and a 128kbps MP3 file, although at 192kbps the difference is much smaller.

In theory, the higher the bitrate, the better the quality - but the larger the file. Therefore, 128kbps and 192kbps are regarded as currently representing the best compromise between the file size and the sound quality. Modern MP3 encoders can also make use of variable bit rate (VBR) MP3 files. A VBR encoder can add bitrate markers to a file, and change the bitrate according to dynamics of the sound. This can reduce the file size further, by only using high bitrates when required. MP3 files are restricted to a bitrate of 320kbps.

Generally speaking, an MP3 file can be around 10 times smaller than its WAV equivalent, although the actual file size will depend on the bitrate and encoder being used. The LAME encoder is considered one of the best around today, along with modern versions of the Fraunhofer encoder. The LAME encoder is said to be better at encoding at 192kbps or above, but does not perform so well below 128kbps.

MP3 is the file format for you if you want to be able to play your music on a wide variety of software and hardware players, and swap tracks easily with friends. If you're looking to store or archive music files, play them back on just a software player or on your PC, you might be better off looking at one of the other, more modern and efficient formats.

AAC - Advanced Audio Coding

AAC is the successor to the MP3 format. The AAC format is quite a considerable improvement on MP3, with the potential for better quality music at smaller file sizes. AAC stands for "Advanced Audio Coding", and was first specified in a 1997 ISO standard, although this initial standard has since been improved. AAC is also sometimes referred to as MP4 Audio. It can support sample rates from 8kHz to 96kHz, which compares to the 48kHz maximum official sample rate of MP3, and files encoded at 150kbps or above are usually good enough to pass for as good as original quality, with the lossy compression being, for most listeners, inaudible. AAC is designed to improve frequency handling above 16kHz, and can have up to 48 channels.

Perhaps the best known implementation of AAC at present is the iPod and Apple's iTunes site, and the success of the iPod and iTunes could well mean that AAC becomes the standard of digital music in the near future. Record companies also support AAC over MP3 because of its flexibility to be used with digital rights management and copyright protection. Nero's AAC encoder is regarded as one of the best that is commercially available, and according to the HydrogenAudio website, Nero and iTunes are considered to be the safe encoders for archiving music onto your computer. Nero's encoder comes with Nero 6.

Software players are now supporting AAC in fairly large numbers and popular players Winamp, Real Player and Windows Media Player all now support the format. The iPod is of course the most well known hardware player to support AAC, although other manufacturers are beginning to support it as well.

Disadvantages to the format are that AAC is heavily patented, which limits the potential for those wishing to build their own software players, and prevents open source developers from using it. The different types of AAC file can lead to confusion, and with many current players only supporting the AAC LC, it's possible for you to have the wrong type of AAC file for your player. Its comparitavely slow encoding time is also something those who want to archive a large music collection will need to consider.

OGG Vorbis

OGG Vorbis is a (supposedly) patent free, open source lossy audio format which has become popular with digital music fans since its initial launch. Vorbis files are generally of better efficiency than MP3, being similar to AAC. Obviously the major difference between Vorbis and AAC is that AAC is a commercial format whereas Vorbis is open source, so Vorbis is more widely used by the online music technology community, and AAC is more widely used by commercial music fans such as those who enjoy iTunes.

Vorbis files may need to be encoded at a slightly higher bitrate to AAC before the sound can pass for original quality, with technology websites suggesting rates between 150kbps and 175kbps depending on the style of music being encoded. Vorbis supports both fixed and variable bitrate encoding, and can encode up to 48kHz, which is lower than AAC, although still higher than 44.1kHz CD quality. Vorbis also supports audio streaming, like RealAudio, and with gapless playback also supported, it is a very versatile format.

Surprisingly for such a comparitavely young format, Vorbis files are supported by a range of both software and hardware players. Their small file size and versatility makes them a strong competitor in the world of digital audio. One drawback is that they require a larger amount of computer processing power to play and encode than other formats; Vorbis is also not as efficient at higher bitrates so those who require very high quality audio may want to look at the alternatives.

RealAudio

Released by Real Networks as long ago as 1995, RealAudio is one of the older audio formats out there, and has become the choice of many online radio stations and music shops for audio streaming. Very few software players support this format, and RealAudio's own RealPlayer is the main player used for RealAudio, although this doesn't allow audio streams to be saved to disk.

RealAudio's major strength is its efficiency at streaming audio at low bitrates, hence its popularity with online radio. It doesn't perform so well at high bitrates and isn't really an alternative to AAC, MP3 and the like for storing digital music.

WMA

WMA is Microsoft's answer to the digital audio revolution, standing for Windows Media Audio. Thanks to the inclusion of Windows Media Player with all versions of Windows, WMA Standard has become one of the most popular lossy audio formats. It can also outperform MP3 at lower bitrates, although listening tests have suggested it does not do so well at the higher end of the scale. To counter this, Microsoft have launched WMA Pro, which, according to HydrogenAudio, was ranked equal to other high quality formats in an informal public listening test. Microsoft have also produced a WMA Lossless codec, a WMA Voice codec for spoken word audio and a multichannel surround sound WMA codec.

WMA enjoys wide support among software players, with Winamp and Windows Media Player - possibly the two most prevalent players - supporting it.

MPC

MPC, or Musepack, was created by Andree Buschmann, and is a very competitive, lesser known lossy audio format at higher bitrates. Its fast encoding and decoding, and open source encoder status are other major benefits, although MPC does not perform as well at lower bitrates, especially under 64kbps. MPC is not suitable for streaming and does not support multichannel, or sample rates above 48kHz.

MPC does not currently enjoy wide support, particularly among hardware players, although this may change in the future. Winamp plug-ins are available for the format.

© John Dalling, 2006

While every attempt is made to ensure the information on this page is correct, the author cannot accept responsibility for the accuracy of the information provided.