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Reduction ratio based on sound quality |
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| Telephone level | 2.5 | Mono | 8 | 96:1 |
| Better than short wave | 4.5 | Mono | 16 | 48:1 |
| Better than AM radio | 7.5 | Mono | 32 | 24:1 |
| Similar to FM radio | 11 | Stereo | 56 ~ 64 | 26 ~ 24:1 |
| Closed to CD | 15 | Stereo | 96 | 16:1 |
| CD level | 15 | Stereo | 112 ~ 128 | 14 ~ 12:1 |
What is MP3?
MP3 means the Layer 3 of MPEG, the international standard compression technology, which provides an excellent quality sound. This technology makes it possible to compress a file down to 1/12 of its original size without much difference in the quality of the sound between MP3 and a CD. This reduced MPEG file can be edited by the user, and more can be added by accessing the files that have "MP3" as the extension name through Internet.
MP3 could be the final encoding technology of the limited human hearing The compression rate takes about 1MB of disk space for one minute of CD sounding quality. Unlike an audio CD, more than 130 popular songs can be converted into MP3 files. This will take more than 10 hours to play back all 130 songs, and will play it back in a near CD quality sound. Most songs take about 50 Mbytes in the WAVE format, but compressed with the MP3 format, the size of the MP3 file will dramatically decrease to 4-5 Mbytes.
Efficient coding techniques for cost-effective processing of digital audio and video data by computers is a must these days. Data reduction of moving pictures and sound is a key technology for any application with limited transmission or storage capacity. In the recent years, tremendous progress has been achieved. While there (still) exist several proprietary formats for audio and video coding, the ISO (International Standardization Organization)/IEC (International Electrotechnical Commission) standardisation body has released an international standard ("MPEG") for powerful audio and video coding tools. By exploiting stereo effects and by limiting the audio bandwidth to that of the human ear, the coding schemes may achieve an acceptable sound quality at even lower bitrates. Layer-3 is the most powerful member of the MPEG audio coding family. For a given sound quality level, it requires the lowest bitrate - or for a given bitrate, it achieves the highest sound quality. Some typical performance data of Layer-3 are as follows:
