Every time you use an MP3 player or an iPod, you’re using compressed audio files, whether you realise it or not. Whilst MP3 is probably the most common compressed audio format, it’s certainly not the only one available.
Manufacturers like to develop and retain technologies that gives them a commercial and technological advantage over their competitors. To this end we as consumers have ended up with a collection of competing, but unfortunately technically incompatible, solutions to the same problem; that of storing large amounts of audio on portable audio players.
Thankfully the majority of manufacturers (but by no means all) of these portable audio players have eased our potential incompatibility problems by making sure that their players can play the majority of compressed audio formats that are in common usage today.
So what are these common compressed audio formats, why do we need them and what are the associated problems with having so many different formats?
Back in the dark ages of computing, not so long ago, computer memory was not so plentiful, or cheap as it is today. As such, storing large amounts of data, such as audio files, was very costly.
As necessity is the mother of invention, the limited quantities of computer memory available prompted the white coated technical boffins to develop fiendishly cunning ways of throwing away most of the audio data from these files, while still retaining a high level of perceived audio quality.
How they do this is rather complicated, but they essentially save space by not storing the bits of the music that we can’t hear. During compression of a 128 kbits/s MP3 file, typically 90% of the audio data is discarded, leaving a file size of one tenth of the original size. This in turn means that your MP3 player is able to store ten times the amount of songs compared to if it had to store the original uncompressed CD data.
MP3 (MPEG-1 Audio Layer 3) is by far the most well known out of all of the audio compression systems available today, and while it may not be as technologically advanced as some of the newer systems, it is the most widely used and provides perfectly adequate results for moderate bit rates for the majority of people’s requirements.
The major benefit of encoding your audio files in MP3 format is that you are pretty much guaranteed you’ll be able to play your resultant files on almost any modern media player or device. It is for this reason that most podcasts choose to adopt the MP3 format as their preferred compression system.
While most people think that MP3 is a free and open source format, it’s not! There are numerous patents owned by a host of different organisations that are applicable to the MP3 technology. This can make official licensing of MP3 technology for use in encoding software or playback devices quite tortuous. Out of all of the organisations that lay claim to the technology underlying MP3s, the German Fraunhofer Society is probably the most notable.
AAC (Advanced Audio Coding) is actually part of the MPEG-2 and MPEG-4 specifications and is designed to be a superior technological replacement for the older MP3 format. AAC is designed to provide improved sonic quality and transparency compared to MP3 files encoded at the same bit rate, although this advantage only becomes dominant for lower bit rates (below 128 kbits/s).
AAC is the default format that Apple have adopted for their iPods, iPhone and iTunes and for their iTunes online music store. Sony has also adopted AAC as the standard audio encoding system for their PlayStation 3 and has been incorporated into their PlayStation Portable and recent Sony Walkman systems. Other companies adopting this format include Nokia and Nintendo (Wii and DSi).
WMA (Windows Media Audio) is Microsoft’s proprietary audio compression system built into its Windows operating system and is the default compression option used for ripping CDs to your computer using Windows Media Player.
Whilst WMA is a proprietary Microsoft system, the technology has been licensed by numerous third parties meaning that if you’ve ripped your entire CD collection onto your computer’s hard drive in WMA format (as I have), then you have a good chance of being able to play these WMA encoded audio files on a host of compatible devices.
I have a Creative ZenMP3 player, which plays WMA files without any problems and I also have two Netgear MP101 media players at home linked to my home network that can stream music from my server in WMA format.
ATRAC (Adaptive Transform Acoustic Coding) is another proprietary audio compression format, this time developed by Sony, originally for their MiniDisc systems in the early 1990s, but has since been used in the company’s range of portable audio players.
Since its inception, ATRAC’s compression algorithm has been improved over the intervening years, with the newer versions offering improved perceived audio quality over earlier versions for similar bit rates.
Unfortunately, ATRAC encoded files are not widely supported by other manufacturers and as such, if you have a Sony branded audio player and have ripped all of your CD selection into ATRAC files, you’ll be extremely limited as to where else you can play your audio files.
While the Ogg Vorbis audio compression format is not hugely popular outside of the geeky computer nerd circles, it is worth a brief mention as a number of commercial “MP3 players” support the format. More importantly though is the Ogg Vorbis system is FREE!
There are no patents or licence issues to worry about if you choose to adopt this system, although compatibility with other media playback devices may prove to be an issue.
All of the above compression systems loose some audio quality in their compression process. FLAC does not, but the downside is that the same sort of compression levels are not achievable.
FLAC files tend to be between 40 to 50% the size of the original audio file, which is not that impressive compared to a typical 10% figure of an MP3 file.
Like anything in life, it’s a balancing act. If you can afford the additional storage space required and want original quality audio, then FLAC is the way to go. For the majority of people however, these tiny improvements in audio quality compared to the space saving benefits of any of the above compression formats will not be worth the penalty of compatibility issues.
While MP3 is the most common and well known of all the audio compression systems, it’s by no means the best. There are a multitude of different audio compression systems available, with just a handful of the most common ones mentioned above.
The choice of compression system can depend on many factors, but for most people, providing the audio quality is reasonably good and the file sizes acceptably small the overriding issue will probably be compatibility.