Bit rate: Difference between revisions

{{Short description|Information transmission rate expressed in bits per second}}

{{Use dmy dates|date=March 2021}}

 

In most computing and digital communication environments, one '''byte per second''' (symbol: '''B/s''') corresponds to 8 bit/s.

 

When quantifying large or small bit rates, [[SI prefix]]es (also known as [[metric prefix]]es or decimal prefixes) are used, thus:<ref>{{cite book | chapter-url=https://ieeexplore.ieee.org/document/5166093 | doi=10.1109/EDST.2009.5166093 | chapter=From millibits to terabits per second and beyond - over 60 years of innovation | title=2009 2nd International Workshop on Electron Devices and Semiconductor Technology | year=2009 | last1=Jindal | first1=R. P. | pages=1–6 | isbn=978-1-4244-3831-0 | s2cid=25112828 }}</ref>

{|

|-

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|align="right"| 1&nbsp;bit/s ||= 1&nbsp;bit/s (one bit per second)

|align="right"| 1,000&nbsp;bit/s ||= 1&nbsp;[[kbit/s]] (one kilobit per second, i.e., one thousand bits per second)

|-

|-

|align="right"| 1,000,000,000&nbsp;bit/s ||= 1&nbsp;[[Gbit/s]] (one gigabit per second, i.e., one [[1000000000 (number)|billion]] bits per second)

 

[[Binary prefix]]es are sometimes used for bit rates.<ref>Schlosser, S. W., Griffin, J. L., Nagle, D. F., & Ganger, G. R. (1999). Filling the memory access gap: A case for on-chip magnetic storage (No. CMU-CS-99-174). CARNEGIE-MELLON UNIV PITTSBURGH PA SCHOOL OF COMPUTER SCIENCE.</ref><ref>{{cite web|url=http://www.ibm.com/docs/en/ibm-mq/7.5?topic=administering-monitoring-file-transfers-that-are-in-progress|title=Monitoring file transfers that are in progress from IBM WebSphere MQ Explorer|date=11 March 2014|access-date=10 October 2014}}</ref>

 

 

{{See also|Data signaling rate}}

 

In digital communication systems, the [[physical layer]] ''gross bitrate'',<ref name="Guimarães">{{cite book |chapter-url= https://books.google.com/books?id=x4jOplMbLx0C&q=gross+bit+rate&pg=PA692 |title=Digital Transmission: A Simulation-Aided Introduction with VisSim/Comm | first =Dayan Adionel | last = Guimarães |publisher=Springer |year=2009 |chapter=section 8.1.1.3 Gross Bit Rate and Information Rate |isbn=9783642013591 |access-date = 10 July 2011}}</ref> ''raw bitrate'',<ref name="Pahlavan">{{cite book |url=https://books.google.com/books?id=WOCrSSfxE-EC&pg=PA133 |title=Networking Fundamentals |author=Kaveh Pahlavan, Prashant Krishnamurthy | publisher= John Wiley & Sons |year=2009 |isbn=9780470779439 |access-date=10 July 2011}}</ref> ''[[data signaling rate]]'',<ref>{{cite book |url= https://books.google.com/books?id=On_Hh23IXDUC&pg=PA135 |title= Network Dictionary |publisher= Javvin Technologies |year = 2007 |isbn= 9781602670006 |access-date=10 July 2011}}</ref> ''gross data transfer rate''<ref name="3G">{{cite book|url=https://books.google.com/books?id=RoJj0zw_pDMC&pg=PA277|title=3G wireless demystified|last1=Harte|first1=Lawrence|last2=Kikta|first2=Roman|last3=Levine|first3=Richard|publisher=[[McGraw-Hill Professional]]|year=2002|isbn=9780071382823|access-date=10 July 2011}}</ref> or ''uncoded transmission rate''<ref name= "Pahlavan" /> (sometimes written as a variable ''R''_b<ref name="Guimarães"/><ref name="Pahlavan"/> or ''f''_b<ref>{{cite book |url=https://books.google.com/books?id=6Hd6WqsgKIMC&pg=PA30 |title=Principles of Digital Communication |author=J.S. Chitode |publisher=Technical Publication |year=2008 |isbn=9788184314519 |access-date=10 July 2011 }}{{Dead link|date=August 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>) is the total number of physically transferred bits per second over a communication link, including useful data as well as protocol overhead.

 

as:

 

The gross bit rate is related to the [[symbol rate]] or modulation rate, which is expressed in [[baud]]s or symbols per second. However, the gross bit rate and the baud value are equal ''only'' when there are only two levels per symbol, representing 0 and 1, meaning that each symbol of a [[data transmission]] system carries exactly one bit of data; for example, this is not the case for modern modulation systems used in [[modem]]s and LAN equipment.<ref>

Lou Frenzel. 27 April 2012,

Electronic Design. 2012.

</ref>

 

For most [[line code]]s and [[modulation]] methods:

 

More specifically, a line code (or [[baseband]] transmission scheme) representing the data using [[pulse-amplitude modulation]] with <math>2^N</math> different voltage levels, can transfer <math>N</math> bits per pulse. A [[digital modulation]] method (or [[passband transmission]] scheme) using <math>2^N</math> different symbols, for example <math>2^N</math> amplitudes, phases or frequencies, can transfer <math>N</math> bits per symbol. This results in:

 

An exception from the above is some self-synchronizing line codes, for example [[Manchester coding]] and [[return-to-zero]] (RTZ) coding, where each bit is represented by two pulses (signal states), resulting in:

 

A theoretical upper bound for the symbol rate in baud, symbols/s or pulses/s for a certain [[bandwidth (signal processing)|spectral bandwidth]] in hertz is given by the [[Nyquist rate|Nyquist law]]:

 

In practice this upper bound can only be approached for [[line coding]] schemes and for so-called [[vestigial sideband]] digital modulation. Most other digital carrier-modulated schemes, for example [[amplitude-shift keying|ASK]], [[phase-shift keying|PSK]], [[quadrature amplitude modulation|QAM]] and [[OFDM]], can be characterized as [[double sideband]] modulation, resulting in the following relation:

 

In case of [[parallel port|parallel communication]], the gross bit rate is given by

 

{{See also|Code rate}}

 

 

The relationship between the gross bit rate and net bit rate is affected by the FEC [[code rate]] according to the following.

 

The connection speed of a technology that involves forward error correction typically refers to the physical layer ''net bit rate'' in accordance with the above definition.

For example, the net bitrate (and thus the "connection speed") of an [[IEEE 802.11a]] wireless network is the net bit rate of between 6 and 54&nbsp;Mbit/s, while the gross bit rate is between 12 and 72&nbsp;Mbit/s inclusive of error-correcting codes.

 

 

 

In communications technologies without forward error correction and other physical layer protocol overhead, there is no distinction between gross bit rate and physical layer net bit rate. For example, the net as well as gross bit rate of Ethernet 10BASE-T is 10&nbsp;Mbit/s. Due to the [[Manchester code|Manchester]] line code, each bit is represented by two pulses, resulting in a pulse rate of 20&nbsp;megabaud.

 

The [[channel capacity]], also known as the [[Shannon–Hartley theorem|Shannon]] capacity, is a theoretical upper bound for the maximum net bitrate, exclusive of forward error correction coding, that is possible without bit errors for a certain physical analog node-to-node [[communication link]].

 

The channel capacity is proportional to the [[analog bandwidth]] in hertz. This proportionality is called [[Hartley's law]]. Consequently, the net bit rate is sometimes called [[digital bandwidth]] capacity in bit/s.

 

{{Main|Network throughput}}

 

The term ''[[throughput]]'', essentially the same thing as '''[[bandwidth (computing)|digital bandwidth]] consumption''', denotes the achieved average useful bit rate in a computer network over a logical or physical communication link or through a network node, typically measured at a reference point above the data link layer. This implies that the throughput often excludes data link layer protocol overhead. The throughput is affected by the traffic load from the data source in question, as well as from other sources sharing the same network resources. See also [[measuring network throughput]].

 

{{Main|Goodput}}

 

 

If no data compression is provided by the network equipment or protocols, we have the following relation:

for a certain communication path.

 

These are examples of physical layer net bit rates in proposed communication standard interfaces and devices:

 

{{For|more examples|list of interface bit rates|spectral efficiency comparison table|OFDM system comparison table}}

 

 

* The original material may be sampled at different frequencies.

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 artifact]]s. 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.

 

 

 

 

A theoretical lower bound for the encoding bit rate for [[lossless data compression]] is the [[source information rate]], also known as the ''entropy rate''.

 

 

 

 

The bit rate of PCM audio data can be calculated with the following formula:

 

For example, the bit rate of a CD-DA recording (44.1&nbsp;kHz sampling rate, 16 bits per sample and two channels) can be calculated as follows:

 

The cumulative size of a length of PCM audio data (excluding a file [[Header (computing)|header]] or other [[metadata]]) can be calculated using the following formula:

 

The cumulative size in bytes can be found by dividing the file size in bits by the number of bits in a byte, which is eight:

 

Therefore, 80 minutes (4,800 seconds) of CD-DA data requires 846,720,000 bytes of storage:

 

The [[MP3]] audio format provides [[lossy data compression]]. Audio quality improves with increasing bitrate:

* 32&nbsp;kbit/s{{snd}} generally acceptable only for speech

* 96&nbsp;kbit/s{{snd}} generally used for speech or low-quality streaming

* 320&nbsp;kbit/s{{snd}} highest level supported by the [[MP3]] standard

 

* 800&nbsp;bit/s{{snd}} minimum necessary for recognizable speech, using the special-purpose [[FS-1015]] [[speech encoding|speech codecs]]

* 2.15&nbsp;kbit/s{{snd}} minimum bitrate available through the open-source [[Speex]] codec

* 32–500&nbsp;kbit/s{{snd}} [[Lossy compression|lossy audio]] as used in [[Ogg Vorbis]]

* 256&nbsp;kbit/s{{snd}} Digital Audio Broadcasting ([[Digital Audio Broadcasting|DAB]]) [[MPEG-1 Audio Layer II|MP2]] bit rate required to achieve a high quality signal<ref>Page 26 of BBC R&D White Paper WHP 061 June 2003, DAB: An introduction to the DAB Eureka system and how it works http://downloads.bbc.co.uk/rd/pubs/whp/whp-pdf-files/WHP061.pdf</ref>

* 400&nbsp;kbit/s–1,411&nbsp;kbit/s{{snd}} [[Lossless compression|lossless audio]] as used in formats such as [[Free Lossless Audio Codec]], [[WavPack]], or [[Monkey's Audio]] to compress CD audio

* 1,411.2&nbsp;kbit/s{{snd}} [[Linear PCM]] sound format of [[CD-DA]]

* 18&nbsp;Mbit/s{{snd}} advanced lossless audio codec based on [[Meridian Lossless Packing]] (MLP)

 

* 16&nbsp;kbit/s{{snd}} [[videophone]] quality (minimum necessary for a consumer-acceptable "talking head" picture using various video compression schemes)

* 128&ndash;384&nbsp;kbit/s{{snd}} business-oriented [[videoconferencing]] quality using video compression

* 40&nbsp;Mbit/s max{{snd}} [[1080p]] [[Blu-ray Disc]] (using MPEG2, MPEG4 AVC or [[VC-1]] compression)<ref>{{Citation | type = white paper | title = Blu-ray Disc Format 2.B Audio Visual Application Format Specifications for BD-ROM Version 2.4 | date = May 2010 | page = 17 | chapter = 3.3 Video Streams | chapter-url = http://www.blu-raydisc.com/assets/Downloadablefile/BD-ROM-AV-WhitePaper_100604%281%29-15916.pdf}}.</ref>

* 250&nbsp;Mbit/s max{{snd}} [[Digital Cinema Package|DCP]] (using JPEG 2000 compression)

 

 

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* [[Audio bit depth]]

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* [https://castr.io/bitrate-calculator/ Live Video Streaming Bitrate Calculator] Calculate bitrate for video and live streams

* [http://dvd-hq.info/bitrate_calculator.php DVD-HQ bit rate calculator] Calculate bit rate for various types of digital video media.