| We hear the term "compression" all the time when it | | | | with MP3 coding, we can reduce a 70MB song down |
| comes to MP3 and MP4 players these days. Where | | | | to below 5MBs! (That is a 92% reduction in size!). |
| did it come from and why do we care? In the last | | | | Now understand this, though: Compression theory |
| article (Data and MP3 Compression: Understanding | | | | itself has been around much longer than MP3s have |
| "Digital"), I explained what a "digital" signal is. | | | | been sold. Why? It gets back to the technology |
| Remember, data can be stored as raw, or "analog" | | | | question posed above. We have now reduced the |
| signals (like cassette tapes, VHS, or records) or they | | | | storage size of the song, but in order to decompress |
| may be digitized (converted into a series of 1's and | | | | the signal requires a lot more signal processing in the |
| 0's) which we can later convert back into its raw | | | | same amount of time. I remember about 7 years |
| format. Digitizing signals allows us to store information | | | | ago having to buy a big internal computer hardware |
| in an errorless format. So why don't we digitize | | | | card to fit inside my computer to watch DVD's from |
| everything? The answer is simple: It takes a lot of 1's | | | | my new DVD-ROM. Why? DVD data is coded in an |
| and 0's to represent the shortest songs, videos or | | | | MPEG-2 format (similiar to MP4). At that time, |
| movies. A standard 5 minute song can take over | | | | computer processors were not fast enough to |
| 70MB (which is 70 mega-bytes; each byte is made up | | | | process the decoding. Now computers are fast |
| of 8 bits or 1's and 0's). That is 560 million 1's and 0's! | | | | enough to process the data with software. Just in |
| That is a lot! Not only do you have to store all of | | | | the past few years have the two technologies now |
| that information, but we need to process it and | | | | collided. MP3 and MP4 players are now a reality for a |
| convert it back to its analog signal in a short amount | | | | variety of reasons: 1) Advanced compression |
| of time. Luckily, fast processing has been around for | | | | techniques have made file sizes even smaller than |
| some time now and formats such as CDs have | | | | ever. 2) Storage hardware has increased into the |
| taken advantage of this. But CDs are limited in space: | | | | 100s of GB range in a very small package. 3) |
| about 700MB (which will hold about 10 songs). The | | | | Processors are small enough, fast enough and cheap |
| space issue definitely became a problem. That is | | | | enough to fit into the palm of your hand. So where |
| when compression techniques were first introduced. | | | | does technology go from here? MP4 (or video |
| How compression works is that we take the 70MB | | | | compression) is building momentum. Still, it is in its |
| signal (as we described above) and by using either a | | | | infancy and it is still lacking in the necessary storage |
| mathematical algorithm or map, we can organize the | | | | and processing requirements it needs to produce the |
| bits in such a way that less bits are required to store | | | | sharpest and clearest video quality that we are now |
| the same amount of information (My next articles will | | | | coming to expect. |
| cover the details about this a bit more). For example, | | | | |