MP3

While of only indirect relevance to "sound cards", a place has to be found somewhere for a technology that took the PC world by storm in the first half of 1999 - and this seems to be the most appropriate.

Derived from the original MPEG standard, MP3 - an abbreviation of MPEG Audio Layer-3 - is one of three coding schemes (Layer 1, Layer 2 and Layer 3) for the compression of audio signals and uses an audio coding technique based on psychoacoustics - the study of how the human brain perceives sound - which has found that it simply can't process a lot of the information the ear picks up. MP3 removes these redundant and irrelevant parts of a sound signal.

The MP3 standard divides the frequency spectrum into 576 frequency bands and compresses each band independently. The human ear is good at hearing mid-range pitch noises, but no so good at high or low pitched noises. These can be heard - but not well enough for the details to be accurately distinguished. These bands can therefore be heavily compressed without any noticeable affect on overall sound quality using a technique known as perceptual coding. Where two sounds occur at the same time, MP3 records only the one that will actually be picked up by the ear. Similarly, a quiet sound immediately following a loud one can be removed, since this wouldn't be picked up anyway. Sounds are also compressed in stereo - if a sound is identical on both stereo channels, it's only stored once - but it appears on both channels when the MP3 file is decompressed and played.

Additionally, MP3 adds a modified Discrete Cosine Transform (DCT) that implements a filter bank, increasing the frequency resolution 18 times higher than that of layer 2. The result in real terms is that MP3 allows compression of CD-quality audio files by a factor of 12 with little loss in quality. About one minute's worth of CD-quality audio can be compressed to about one megabyte of data - so a typical 4-minute CD track can be stored in a file of between 3.5MB and 5MB. An MP3 file - they use the file extension .mp3 - can also contain information about the file itself in a tag. The tag can contain things like the artist's name, a graphic (usually the CD cover art), a URL for further information, the song's lyrics, the genre, etc.

In the mid-1990s students at US college campuses began to use MP3 technology to trade recordings between themselves - and it quickly became part of everyday campus life. It was only slowly emerging into the mainstream - until the Recording Industry Association of America (RIAA) decided to sue Diamond Multimedia over its distribution of a Korean invention called the Rio in the autumn of 1998. This Sony Walkman-like device was essentially an MP3 storage device capable of playing up to an hour of MP3-coded music. The original suit failed to prevent the Rio coming to market and, following an appeal, the case was finally thrown out in June of 1999, - the court finding that the Rio did not qualify as a "digital audio recording device" and was therefore not subject to the restrictions of the US 1992 Audio Home Recording Act. What the ill-conceived lawsuit did succeed in doing was drawing national attention to MP3 which, almost overnight, metamorphosising it from an underground movement among Internet-savvy technophiles to a pop culture phenomenon.

Most MP3 files will have been produced from material originating on an audio CD. This is a two-stage process, the first involving the conversion of tracks from the CD-DA digital audio format to WAV format. This step is crucially important, and unavoidable. There are some programs that can produce an MP3 directly from CD audio, but they accomplish this by performing an audio extraction from the CD as the initial step in the process. The task is performed by specialised programs known as CD-Rippers. The CD-Ripper reads the tracks of an audio CD digitally and writes them to hard disk as WAV files. A 4-minute track occupies around 40-50MB in WAV format, so the conversion of an entire CD requires a large amount of hard disk space.

The second stage in the process is to convert the .wav files to .mp3 format. This step also involves the use of specialised software, and the programs that perform this task are known as MP3 Encoders. MP3 files can be produced using a variety of compression rates, allowing users to choose their optimal mix of quantity and quality. Typically, the following options are available:

"CD quality" - compressed at 12:1 at rates of between 128 Kbit/s at the low end and up to 192 Kbit/s at the high end

"Near-CD quality" - compressed at around 18:1, and

"FM Radio Quality" (Real Audio), be compressed 70:1 at a rate of 64 Kbit/s.

The majority of the MP3 files available on the Internet are encoded at 44kHz and 128 Kbit/s - a bitrate which results in a good quality/size ratio MP3 file. Encoding at 192 Kbit/s will produce a superquality result - but at the cost of a considerably larger file size. Tracks recorded at 64 Kbit/s and below are sampled at 22kHz. The reverse process - converting MP3 files to CD audio tracks - also involves two discrete stages. The decoding of an MP3 file to a WAV file is performed by a specialised program known as an MP3 Decoder. Getting the WAV file to CD is a function of the various specialised applications that exist for creating CDRs or CD-RWs, such as Easy CD Creator or WinonCD.

Notwithstanding Diamond's success in the US courts, there are issues concerning the use of MP3 technology. Whilst the British Phonographic Industry (BPI) maintain that it is illegal to make copies of a CD/tape/record even if it is for your own use, this is "unenforceable" under UK law and in reality the practice is widespread. Downloading licensed MP3 files from the Internet is perfectly legal, but it is illegal to encode MP3s and trade them with others unless this is done with the express permission of the copyright holder of the music. There are many legal tracks in MP3 format available freely on the Internet that have the permission of their copyright holders - mostly by unknown artists looking for free publicity. However, it's generally accepted that the vast majority of MP3 music files are illegal - they are unlicensed recordings of copyrighted work - and though there are some major artists who have sought to promote their music over the Internet using MP3, this has invariably been met with opposition. Interestingly, shortly after its courtroom success, Diamond appeared to be making moves to pacify the record labels with the announcement that the new model will feature anti-piracy software to prevent unauthorised copying of MP3 files and be upgradeable, via the Internet, to play whatever standard was ultimately recommended by the Secure Digital Music Initiative (SDMI).

One company that is unlikely to be making an MP3 player in the near future is Sony, the inventor of MiniDisc (MD), which has been the emerging digital audio recording standard of the late 1990s. The Rio is both lighter and smaller than most MD players, however, and has the additional advantage of containing no moving parts. This means that no matter how roughly handled, unlike CD or MD, the music won't skip a beat. The Rio also exerts less of a power drain than laser-based products, yielding a claimed 12 hours from a single alkaline battery.

The first Rio device came to market towards the end of 1998, bundled with conversion software capable of digitally extracting CD audio and creating 64-, 80-, or 128 Kbit/s MP3 files. The upper and lower rates equate to 33 minutes of FM quality and 66 minutes of CD quality capacity respectively, from the device's 32MB of internal memory. Storage capacity can be expanded, up to 64MB, via an add-in SmartMedia flash memory card. Mid-1999 - following the rejection of the RIAA's lawsuit and the acquisition of Diamond by graphics-chip manufacturer S3 - saw the Rio business spun-off to a newly formed RioPort division and the announcement of a new model providing double the on-board memory of the earlier model, expandable to 96MB. The incorporation of IBM's 340MB microdrive unit - 1in in size and weighing only 16-grams - into subsequent Rios boosted capacity to up to six hours of near-CD quality MP3 music.

In 2000 a number of players appeared - both portable and designed to complement home hi-fi systems - that handled both conventional CDs and recordable CDs containing MP3-encoded tracks. Whilst these may not have been "skip-free", this was more than compensated for by their massive, 10-hour capacity. If there had been any doubt about MP3's acceptance into the mainstream before, they were removed by the participation of onsumer giants such as Philips Electronics in this marketplace.

MP3 may have been a phenomenon of the late 1990s, but it will almost certainly be eclipsed early in the new millennium. Since its development in 1995 a number of new formats have emerged - many of which give even better compression and comparable quality. AAC (Advanced Audio Compression), for example, can produce files that are 30% to 40% smaller than MP3 files, whilst retaining their level of quality.

Original text: http://www.pctechguide.com/11sound_MP3.htm