Today it is difficult to find a person who is unfamiliar with the three-letter acronym – MP3.Vot only when you start to ask what it is and how stands, some people puzzled shrug. What is mp3?
MP3 – the most popular format for storing and transmitting digital information using signal compression. Format MP3, or MPEG Audio Layer-3, was developed by Fraunhofer IIS and Thomson. Compared with WAV-files, which are copies of tracks Audio CD (PCM, 16 bit, Stereo, 44,1 kHz), MP3-track takes much less disk space. On ordinary CD-R/RW-blanke can store over 11 hours of music is quite decent quality.
High compression ratio in MP3 achieved through a rather complex encoding algorithm. Used as the mathematical methods of compression, and the peculiarities of human hearing (psychoacoustic model) masking effect of the weak sound of one frequency over a loud sound the same or adjacent frequencies, reduced sensitivity to the gentle sound of the ear immediately after a high, resistance to the sounds below a certain volume level.
Audio stream encoding is divided into equal sections (frames). Each of the frames is encoded separately with different parameters and contains a title in which the parameters are indicated. Compression can be done with different quality and size of the final file, respectively. Learn more about Cheap MP3′s.
The compression ratio is characterized bitrate (bitrate) – amount of transmitted information per unit of time. MP3 files are usually encoded with bitrates from 64 to 320 kilobits per second (kbps or kb / s), and a variable bit rate (VBR) – where each frame uses a different, optimal for the site, and bitrate.
Original signal with filters is divided into several frequency bands, each band is determined by the value of the masking effect of neighboring bands, and previous frame, minor signals ignored. For the remaining data for each band is determined by how many bits can be sacrificed to the losses were below the masking effect. In this work a psychoacoustic model is completed, and the resulting flow of additional compressed Huffman (like RAR archiver).
On what is based the idea of compressing audio to MP3?
Certainly, turning to his friend, screened off from the outside world “muzofonom” you noticed how unnaturally loud it starts to answer your questions, because your voice is heard by him under the roar of a rock concert, it sounds to him unusually quiet – a feature of human perception. And it’s not so much the severity of hearing loss, but in the ability of the brain to “digest” the sound information: do not respond to impulses, power below a certain level, after a strong thunder did not hear a whisper, etc.
These and enjoy to create MP3-encoders, each of which can be implemented in their own, varied depending on the goals and objectives of the so-called psychoacoustic model, where we can neglect the relatively weak signals.
Original audio signal is divided into blocks, called frames, each of which uses a special encryption algorithm, and compression settings for different frames may differ significantly from each other. During encoding blocks of source signal is split into several components band. For each of them calculated the value of so-called masking effect of a weak signal from a neighbor more powerful range or from a previous frame. Then depending on the results of the secondary sounds are removed, that will not be audible “average” person because of the moment over the loud signal. Also, take into account the inability of most people to distinguish between high-frequency signals (above 16 kHz).
Quality and value
One of the most important characteristics of a MP3-file bitrate – velocity data to be processed, or the total amount of information transmitted per unit of time. This value does not depend on the flow contains a mono or stereo.
Bitrate of 128 Kbps with a light hand Fraunhofer IIS has been recognized for the best use of the Internet, and some manufacturers of encoders is widely believed that this rate is sufficient to encode the music with a quality close to the Audio CD. However, it is not. On a good audio equipment irreparable losses become noticeable.
The higher the bitrate, the more disk space is required to store the final MP3-file, but, as a rule, the higher the quality of the encoded signal. In general, each entry has a bit rate of applications.
Even professional experts with a good ear for music sometimes can not distinguish between good equipment on the sound track Audio CD and its image encoded in the MP3-file with a low compression ratio, such as 4:1 (320 Kbps). Same for the average music fan, this difference is almost imperceptible at a flow rate of 192-256 Kbps.
If you are dealing only with computer speakers or inexpensive consumer radios, the encoding and then listening to songs is enough 160-192 Kbps. To compress rapidly aging pop music, as well as “laid out” music archive on the network is fine and 128 Kbps. Bitrate values below 128 Kbps fail to achieve adequate sound quality. 64-96 Kbps speed is most often used to compress audiourokov language, lectures, interviews, and audio broadcasting.