 |
|
|
 |
||
 |
|
|
|
|
|
|
|
|
|
|||||||||||||||||
 More than 30 years have passed since Julie Andrews ran down an Austrian mountain slope singing "The hills are alive with the sound of music ....". Today, it is the Internet that is alive with the sound of music, thanks to the extraordinary success of MP3 - or MPEG2.5 Layer III, to give it its official title. Developed by the Fraunhofer Institute and Thomson Multimedia, MP3 is an audio compression standard that allows digital music files to be compressed by a factor of ten without compromising quality. For example, a typical song of about five minutes will occupy about 50Mbytes on a standard compact disk but this can be reduced to just 5Mbytes if MP3 compression is used. Because MP3 files occupy much less space on a hard disk and cut the download time by an order of magnitude, it has become the de facto standard for the distribution of music through the Internet. Initially, MP3 files were used to play music on personal computers via media player software. In 1998 the first dedicated portable MP3 file players became available. Pioneered by Diamond Multimedia's Rio and Saehan's MP3Man, these players generally store music in Flash memory and are 'loaded' with music using a PC and a serial interface. It is no exaggeration to say that today we are on the threshold of a major revolution in the way that music is stored and distributed, one that could eventually make compact disks, minidisks, tapes and other physical media obsolete.  The new breed of 'mechaless' (a contraction of mechanism-less) music players has advantages for both the manufacturer and the consumer: because the equipment has no precision mechanical or optical components, it is cheap to manufacture and highly resistant to shock and vibration. Players can be built with internal Flash memory or an interface for external memory cards. A 64Mbyte memory card, for example, could store over an hour's worth of music. In fact, as shown below, almost anyone who can assemble a PCB can build a solid-state MP3 music player, thanks to ST's recently announced STA013 MP3doc™ chip. The only other components needed to build an MP3 music player are a Flash memory to store the music, a low-cost microcontroller, a digital-to-analog con- verter, a small audio power amplifier and a DC-DC converter to power the system. ST is the only chip manufacturer that can supply all of these components, allowing designers to add MP3 music playback to their products simply, easily and cost effectively.  COMPRESSION WITHOUT COMPROMISE The human ear is very sensitive to audio errors so compressing an audio waveform by a factor of 10 without introducing an unpleasant loss of quality requires a sophisticated coding scheme which, in turn, implies a sophisticated decoding algorithm. This is achieved in the STA013 by means of a proprietary Very Long Instruction Word (VLIW) DSP core developed by ST specifically for audio applications and already used in a wide range of embedded applications such as Dolby digital processing and audio enhancement. The decoder core of the STA013 implements demultiplexing and error correction, Huffman decoding, inverse quantization, inverse discrete cosine transform and filter-bank reconstruction from 32 sub-bands into a single stereo output signal. In addition, software development is reduced to the small amount of code needed to allow the system controller to bootstrap the STA013. The price of the STA013 - only $9 in volume - includes all the royalties for the MP3 decoder license ! WHERE NEXT? The STA013 enables a host of interesting applications apart from personal music players. For example, in a car or home stereo system, an 8Gbyte hard disk drive could be used to store the equivalent of about 150 CDs, with instant access to any track. Juke boxes may never be the same again. In future, they will offer vastly increased selections and be immune to mechanical failure. A major benefit of DSP-based solutions such as the STA013 is that they can be upgraded and enhanced by adding new code to the embedded memory. ST has already developed an enhanced version of the STA013 that includes an Adaptive Pulse Code Modulation (ADPCM) decoder, giving designers the possibility of adding voice recording and playback functions to a MP3 player. Another version planned for the future will include an MP3 encoder in addition to the decoder. An interesting application proposed for this version is in car stereos, where it could be used for time-shifting radio programs for later listening. .... if your mobile phone rings in the middle of an interesting news bulletin, your car radio will simply compress and record the rest of the news bulletin and play it back when you are ready!" Today MP3 is the undisputed market leader in audio compression but it will be replaced by other standards in the future. The main problem is piracy. Understandably, the music industry has not welcomed a technology that allows copyright music to be distributed freely. The success of MP3 has accelerated the development of a digital music format which includes protection against making multiple copies of copyright music - the Secure Digital Music Initiative, in which ST is a participant. Other coding standards are also being considered, such as Advanced Audio Codec (AAC), VQ, and an evolution of Sony's ATRAC. ST follows closely the evolution of new standards for digital music distribution and plans to introduce dedicated DSP solutions for all major standards. Whichever standard emerges as the winner, ST's DSP-based technology will ensure that it plays a key role in the digital music revolution.  |
|
||||||||||||||||||
|
|
 |
|
|
|
|
||
