What is MP3?

MP3 is a short for MPEG-1 Audio Layer 3 and it is a digital audio encoding format. It greatly reduces the amount of the data required to represent the audio recording and it uses a lossy compression algorithm. Even if the algorithm used is lossy in nature, the sound quality of the MP3 file is very good and a normal listener cannot differentiate between the MP3 file and the original uncompressed audio file.

The lossy compression algorithm used is very effective as it can be used to produce files that are 1/10th of the size of the original uncompressed file. The compression achieved depends on the bitrate setting used for the compression. A mid-range bitrate of 128kbit/s will compress a file to 1/10th of its size and the quality of the compressed file also depends on the bitrate setting used for carrying out the compression process.

Perceptual Audio Coding is the underlying principle used for creating MP3 files. Under this, all the irrelevant and redundant parts of the sound signal are removed in order to reduce the size of the file. The parts of the signal which are not audible to human ear are removed from the signal and this reduces the size of the file by a considerable amount. Human ear can hear sounds in the range of 20 Hz to 20 KHz and this fact is used to decide the components of the sound signal that are to be removed from the original uncompressed signal. As these parts are already not audible, removing them from the file doesn't make a difference to a normal listener and so, he cannot make out the difference between the uncompressed file and the compressed file. End result is a small file with good sound quality.

MP3 format is very popular as it's very easy to transfer a file in mp3 format when compared to transferring a file in WAV format. However, mp3 format suffers from several limitations and some of them are :

Frequency resolution is limited and this decreases the coding efficiency.
There's no scale factor band for the frequencies above 15.5/15.8 KHz
Aliasing compensation stage is required for handling aliasing issues and this increases the amount of energy to be coded in the frequency domain. End result is a decrease in the coding efficiency
The overall delay concerned with Encoder/Decoder is not defined.