Data and MP3 Compression: Why Do We Compress?

By: Matthew Bredel
In the last article (Data and MP3 Compression: Understanding "Digital"), I explained what a "digital" signal is. Remember, data can be stored as raw, or "analog" signals (like cassette tapes, VHS, or records) or they may be digitized (converted into a series of 1's and 0's) which we can later convert back into its raw format. Digitizing signals allows us to store information in an errorless format. So why don't we digitize everything? The answer is simple: It takes a lot of 1's and 0's to represent the shortest songs, videos or movies. A standard 5 minute song can take over 70MB (which is 70 mega-bytes; each byte is made up of 8 bits or 1's and 0's). That is 560 million 1's and 0's! That is a lot! Not only do you have to store all of that information, but we need to process it and convert it back to its analog signal in a short amount of time. Luckily, fast processing has been around for some time now and formats such as CDs have taken advantage of this.

But CDs are limited in space: about 700MB (which will hold about 10 songs). The space issue definitely became a problem. That is when compression techniques were first introduced. How compression works is that we take the 70MB signal (as we described above) and by using either a mathematical algorithm or map, we can organize the bits in such a way that less bits are required to store the same amount of information (My next articles will cover the details about this a bit more). For example, with MP3 coding, we can reduce a 70MB song down to below 5MBs! (That is a 92% reduction in size!). Now understand this, though: Compression theory itself has been around much longer than MP3s have been sold. Why? It gets back to the technology question posed above. We have now reduced the storage size of the song, but in order to decompress the signal requires a lot more signal processing in the same amount of time. I remember about 7 years ago having to buy a big internal computer hardware card to fit inside my computer to watch DVD's from my new DVD-ROM. Why? DVD data is coded in an MPEG-2 format (similiar to MP4). At that time, computer processors were not fast enough to process the decoding. Now computers are fast enough to process the data with software. Just in the past few years have the two technologies now collided. MP3 and MP4 players are now a reality for a variety of reasons: 1) Advanced compression techniques have made file sizes even smaller than ever. 2) Storage hardware has increased into the 100s of GB range in a very small package. 3) Processors are small enough, fast enough and cheap enough to fit into the palm of your hand. So where does technology go from here? MP4 (or video compression) is building momentum. StillFree Web Content, it is in its infancy and it is still lacking in the necessary storage and processing requirements it needs to produce the sharpest and clearest video quality that we are now coming to expect.

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