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Jun 17, 2011

What Is The Bitrate? What You Should Know About It.

With the term “bitrate” we face at the mention of audio and video formats. To understand this term, you must master the process of compressing and encoding files. German scientists have laid the general principle of file compression with minimal loss. On the example of coding the original MP3 sound file is cut into fragments, the duration of 50 milliseconds, each of which is analyzed separately. In the analysis of the fragment is decomposed into harmonics of the Fourier method, of which, in accordance with the theory of sound perception by the human ear thrown those harmonics that people perceive worse than the rest. These are quieter harmonics on the back of the higher ones. As a result, emitted sounds are masked due to the inertia of hearing. The information about the harmonics left after filtering and recorded in the MP3 file, which results in a much smaller than the original WAV.
WAV-file contains detailed information about the original sound, digitized and quantized with a frequency of 44kHz. This information is stored on ordinary audio-CD. When playing there is the inverse transformation, in which the remaining harmonic is re-converted into sound waves. Some of the information about the original signal was lost, because the sound is not identical to the original. But throwing irrelevant sounds, so the human ear cannot distinguish the signal from the original order, which was packed to MP3.
Bitrate is the amount of information per unit time. Its essence – how much information about every second of recording we can spend. Naturally, as it is smaller, the smaller the size of the files have the same length of time, thus will have to throw more “extra” harmonics. Bitrates are units of measurement – kilobits per second (Kbps) and megabits per second (Mbps). MP3 audio compression algorithm is often used with 128 kbps compression. They are of two types: fixed and variable. For example, when a video compression is used with a constant bitrate a fixed amount of data is used to encode a second film. In the case of variable bitrate the codec installs eigenvalue bitrate depending on the scenes of the movie. For example, when encoding to mpeg the gain in compression is mostly obtained by retaining only the difference between adjacent frames. During a slow scene change the difference between frames is small and thus can reduce the amount of a bit rate required for playback of these scenes. However, with the abrupt change of scenes in the film, the differences in staffing increase dramatically in size and require more bitrate to play such scenes. In contrast to the constant bit rate, at a variable one cannot predict the size of the output file, it depends on the ratio of “fast” and “slow” scenes in the film.
Regarding to radio online, the downloadable sound quality of radio stations with the network also can be analyzed by bitrate. The choice between 48kbps and 128 kbps bit rate, I hope, will introduce you to a long meditation.
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