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In telecommunications and computing, bitrate (sometimes written bit rate, or as a variable Rbit) is the number of bits that are conveyed or processed per unit of time. In digital multimedia, bitrate is the number of bits used per unit of time to represent a continuous medium such as audio or video. It is quantified using the bit per second (bit/s) unit or some derivative such as Mbit/s. While often referred to as "speed", bitrate does not measure distance/time but quantity/time, and thus should be distinguished from the "propagation speed" (which depends on the transmission medium and has the usual physical meaning).
Usage notes The formal abbreviation for "bit per second" is "bit/s" (not "bits/s"). In less formal contexts the abbreviations "b/s" or "bps" are often used, though this risks confusion with "bytes per second" ("B/s", "Bps"). Even less formally, it is common to drop the "per second", and simply refer to "a 128 kilobit audio stream" or "a 100 megabit network". Note that binary prefixes are used in most operating system and software, and SI prefixes are used in most hardware. For non-technical people this may lead to a confusion between the transfer rate displayed by software and the transfer rate advertised. e.g. Cable high speed internet advertised as 3 Mbit/s and your computer most likely uses Mbytes/s (binary M) and displays a download rate that never tops 380 Kbytes/s. "Bitrate" is sometimes used interchangeably with "baud rate", which is correct only when each modulation transition of a data transmission system carries exactly one bit of data (something not true for modern modem modulation systems, for example). Similarly, hertz, the SI unit of frequency, is not precise without some context, such as the number of bits carried per cycle. For large bitrates, SI prefixes are used: When describing bitrates, binary prefixes are almost never used and SI prefixes are almost always used with the standard, decimal meanings, not the computer-oriented binary meanings. Binary usage is more often seen when the unit is the byte/s, and is not typical for telecommunication links. Sometimes it is necessary to seek clarification of the units used in a particular context. Progress Looking at the development of transmission speeds, Moore's Law may be applied not only to transistor densities, but as well to transmission speeds: bitrates doubled about every 18 months. Bitrates in multimedia In digital multimedia, bitrate represents the amount of information, or detail, that is stored per unit of time of a recording. The bitrate depends on several factors: If lossy data compression is used on audio or visual data, differences from the original signal will be introduced; if the compression is substantial, or lossy data is decompressed and recompressed, this may become noticeable in the form of compression artifacts. Whether these affect the perceived quality, and if so how much, depends on the compression scheme, encoder power, the characteristics of the input data, the listener’s perceptions, the listener's familiarity with artifacts, and the listening or viewing environment. Experts and audiophiles may detect artifacts in many cases in which the average listener would not. Some musicians enjoy the distinct artifacts of low bitrate (sub-FM quality) encoding and there is a growing scene of net labels distributing stylized low bitrate music. The bitrates in this section are approximately the minimum that the average listener in a typical listening or viewing environment, when using the best available compression, would perceive as not significantly worse than the reference standard: Audio (MP3) Other audio Video (MPEG2) Notes For technical reasons (hardware/software protocols, overheads, encoding schemes, etc.) the actual bitrates used by some of the compared-to devices may be significantly higher than what is listed above. For example: See also Bandwidth conversion Allow easy conversion from kbit/s to MB/h to GB/day to TB/month to ... Bandwidth calculator online Bitrates of DVB-S TV and radio channels | ||||||||
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