How Mp3 works ?

MP3 stands for MPEG 1 - Layer 3. (Full form of MPEG is Moving picture expert group). MP3 is a digital audio encoding format used to reduce the size of audio files still maintaining very good audio quality. Unlike other movements -- for example, the introduction of the cassette tape or the CD -- the MP3 movement started not with the industry itself but with a huge audience of music lovers on the Internet. Though several other audio formats like mp4 audio etc., are introduced, the MP3 format has had, and will continue to have, a huge impact on how people collect, listen to and distribute music.

CD - WAV file format:
Before knowing what MP3 format is actually, we need to know about WAV files. A CD stores a song as digital information using an uncompressed, high-resolution format called WAV. Here's what happens when a CD is created:

* Music is sampled 44,100 times per second. The samples are 2 bytes (16 bits) long.
* Separate samples are taken for the left and right speakers in a stereo system.

Sampling is a process by which, magnitudes of the waveform at instances separated by equal intervals (mostly) are only taken. So for a second of music waveform, the waveform magnitudes are noted 44,100 times and converted to digital format. To have better listening experience, we use stereo systems.

So a CD stores a huge number of bits for each second of music:

44,100 samples/second * 16 bits/sample * 2 channels = 1,411,200 bits per second.

Going by this calculation, if an average song is three minutes long, then the average song on a CD consumes about 32 million bytes (about 31 MB) of space. Streaming audio in internet can't be done with this format, as the size of the file is too big for 3 minutes audio and we have to buffer for hours to hear the 3 mins song with an internet connection of low speed.

MP3 Format:
To overcome this issue, new formats are developed to reduce the size of the song stored digitally. However MP3 format become the real winner among the users. MP3 formats can reduce the size by an factor of 10 to 14, without appreciably reducing the quality of the song. Thus an average song can be reduced to 3MB in size with this format. Hence streaming becomes easy, and we don't need to buffer for a long time to hear the song.

Is it possible to compress a song without hurting its quality? We use compression algorithms for images all the time. For example, a GIF file is a compressed image. So is a JPG file. We create Zip files to compress text. So we are familiar with compression algorithms for images and words and we know they work. To make a good compression algorithm for sound, 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 -- by a factor of 10 at least. (If you would like to learn more about the specific compression algorithms, see the links at the end this article.) 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.

From this description, you can see that MP3 is nothing magical. It is simply a file format that compresses a song into a smaller size so it is easier to move around on the Internet and store.

But however, as always, danger comes with technology. Because of the reduced size and good sound quality, it becomes easy for people to move audio songs from one place to other, via internet, CDs etc., and thus leading to increased piracy.


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