To make a good compression a technique called perceptual noise shaping is used. It is "perceptual" partly because the MP3 format uses characteristics of the human ear to design the compression algorithm. For example:
- there are certain sounds that the human ear cannot hear.
- There are certain sounds that the human ear hears much better than others.
- If there are two sounds playing simultaneously, we hear the louder one but cannot hear the softer one.
Using facts like these, certain parts of a song can be eliminated without significantly hurting the quality of the song for the listener. Compressing the rest of the song with well-known compression techniques shrinks the song considerably. When you are done creating an MP3 file, what you have is a "near CD quality" song. The MP3 version of the song does not sound exactly the same as the original CD song because some of it has been removed, but it's very close. MP3 is so popular because of its small size, but mainly because of a high quality which can be found in few megabytes.
MP3 players are for playing MP3 files on a computer. The most popular are Winamp or Sonique. In the last two years portable MP3 players has been introduced. We can divide them into three groups:
The first one looks like standard Discman with the slight difference. It can read MP3 files from a CD, and because these are smaller size, we can keep about 200 songs on one CD.
- small prize
- it can read normal audio CD too
- big dimensions
- sometimes problems playing by walking
The second is players with flash memory into which we can record songs straight from computer. The number of songs that we can record to this player depends on size of its disc, but it ranges from 16 songs to 5 000 songs.
Advantages: -it is stored device too
-we can listening a radio or record sounds
Disadvantages: -smaller memory (128 or 256 MB =2-4 hours of data in MP3 format)
Third possible are devices which use hard disc. Capacity of these hard discs is 20-60 GB so we can save on them all our CDs in MP3 format.
Advantages: -big memory
Disadvantages: -big dimensions