Bit rate

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Bit rates(data-rate units)

Name	Symbol	Multiple
bit per second	bit/s	1	1
Metric prefixes(SI)
kilobit per second	kbit/s	103	10001
megabit per second	Mbit/s	106	10002
gigabit per second	Gbit/s	109	10003
terabit per second	Tbit/s	1012	10004
Binary prefixes(IEC 80000-13)
kibibit per second	Kibit/s	210	10241
mebibit per second	Mibit/s	220	10242
gibibit per second	Gibit/s	230	10243
tebibit per second	Tibit/s	240	10244

Intelecommunicationsandcomputing,bit rate(bitrateor as a variableR) is the number ofbitsthat are conveyed or processed per unit of time.

The bit rate is expressed in the unitbit per second(symbol:bit/s), often in conjunction with anSI prefixsuch askilo(1 kbit/s = 1,000 bit/s),mega(1 Mbit/s = 1,000 kbit/s),giga(1 Gbit/s = 1,000 Mbit/s) ortera(1 Tbit/s = 1,000 Gbit/s).The non-standard abbreviationbpsis often used to replace the standard symbol bit/s, so that, for example, 1 Mbps is used to mean one million bits per second.

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

Prefixes

When quantifying large or small bit rates,SI prefixes(also known asmetric prefixesor decimal prefixes) are used, thus:

0.001 bit/s	= 1 mbit/s (one millibit per second, i.e., one bit per thousand seconds)
1 bit/s	= 1 bit/s (one bit per second)
1,000 bit/s	= 1kbit/s(one kilobit per second, i.e., one thousand bits per second)
1,000,000 bit/s	= 1Mbit/s(one megabit per second, i.e., one million bits per second)
1,000,000,000 bit/s	= 1Gbit/s(one gigabit per second, i.e., onebillionbits per second)
1,000,000,000,000 bit/s	= 1Tbit/s(one terabit per second, i.e., onetrillionbits per second)

Binary prefixesare sometimes used for bit rates. The International Standard (IEC 80000-13) specifies different symbols for binary and decimal (SI) prefixes (e.g., 1KiB/s = 1024 B/s = 8192 bit/s, and 1MiB/s = 1024 KiB/s).

In data communications

Gross bit rate

See also:Data signaling rate

In digital communication systems, thephysical layergross bitrate,raw bitrate,data signaling rate,gross data transfer rateoruncoded transmission rate(sometimes written as a variableR_borf_b) is the total number of physically transferred bits per second over a communication link, including useful data as well as protocol overhead.

In case ofserial communications,the gross bit rate is related to the bit transmission time$T_{\text{b}}$ as:

$R_{\text{b}}={1 \over T_{\text{b}}},$

The gross bit rate is related to thesymbol rateor modulation rate, which is expressed inbaudsor symbols per second. However, the gross bit rate and the baud value are equalonlywhen there are only two levels per symbol, representing 0 and 1, meaning that each symbol of adata transmissionsystem carries exactly one bit of data; for example, this is not the case for modern modulation systems used inmodemsand LAN equipment.

For mostline codesandmodulationmethods:

${\text{symbol rate}}\leq {\text{gross bit rate}}$

More specifically, a line code (orbasebandtransmission scheme) representing the data usingpulse-amplitude modulationwith$2^{N}$different voltage levels, can transfer$N$bits per pulse. Adigital modulationmethod (orpassband transmissionscheme) using$2^{N}$different symbols, for example$2^{N}$amplitudes, phases or frequencies, can transfer$N$bits per symbol. This results in:

${\text{gross bit rate}}={\text{symbol rate}}\times N$

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

${\text{gross bit rate = symbol rate/2}}$

A theoretical upper bound for the symbol rate in baud, symbols/s or pulses/s for a certainspectral bandwidthin hertz is given by theNyquist law:

${\text{symbol rate}}\leq {\text{Nyquist rate}}=2\times {\text{bandwidth}}$

In practice this upper bound can only be approached forline codingschemes and for so-calledvestigial sidebanddigital modulation. Most other digital carrier-modulated schemes, for exampleASK,PSK,QAMandOFDM,can be characterized asdouble sidebandmodulation, resulting in the following relation:

${\text{symbol rate}}\leq {\text{bandwidth}}$

In case ofparallel communication,the gross bit rate is given by

$\sum _{i=1}^{n}{\frac {\log _{2}{M_{i}}}{T_{i}}}$

wherenis the number of parallel channels,M_iis the number of symbols or levels of themodulationin theithchannel,andT_iis thesymbol duration time,expressed in seconds, for theith channel.

Information rate

See also:Code rate

Thephysical layernet bitrate,information rate,useful bit rate,payload rate,net data transfer rate,coded transmission rate,effective data rateorwire speed(informal language) of a digitalcommunication channelis the capacity excluding thephysical layerprotocol overhead, for exampletime division multiplex(TDM)framing bits,redundantforward error correction(FEC) codes, equalizer training symbols and otherchannel coding.Error-correcting codes are common especially in wireless communication systems, broadband modem standards and modern copper-based high-speed LANs. The physical layer net bitrate is the datarate measured at a reference point in the interface between thedata link layerand physical layer, and may consequently include data link and higher layer overhead.

In modems and wireless systems,link adaptation(automatic adaptation of the data rate and the modulation and/or error coding scheme to the signal quality) is often applied. In that context, the termpeak bitratedenotes the net bitrate of the fastest and least robust transmission mode, used for example when the distance is very short between sender and transmitter.Some operating systems and network equipment may detect the "connection speed"(informal language) of a network access technology or communication device, implying the current net bit rate. The termline ratein some textbooks is defined as gross bit rate,in others as net bit rate.

The relationship between the gross bit rate and net bit rate is affected by the FECcode rateaccording to the following.

net bit rate ≤ gross bit rate ×code rate

The connection speed of a technology that involves forward error correction typically refers to the physical layernet bit ratein accordance with the above definition.

For example, the net bitrate (and thus the "connection speed" ) of anIEEE 802.11awireless network is the net bit rate of between 6 and 54 Mbit/s, while the gross bit rate is between 12 and 72 Mbit/s inclusive of error-correcting codes.

The net bit rate of ISDN2Basic Rate Interface(2 B-channels + 1 D-channel) of 64+64+16 = 144 kbit/s also refers to the payload data rates, while the D channel signalling rate is 16 kbit/s.

The net bit rate of the Ethernet 100BASE-TX physical layer standard is 100 Mbit/s, while the gross bitrate is 125 Mbit/s, due to the4B5B(four bit over five bit) encoding. In this case, the gross bit rate is equal to the symbol rate or pulse rate of 125 megabaud, due to theNRZIline code.

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 Mbit/s. Due to theManchesterline code, each bit is represented by two pulses, resulting in a pulse rate of 20 megabaud.

The "connection speed" of aV.92voicebandmodemtypically refers to the gross bit rate, since there is no additional error-correction code. It can be up to 56,000 bit/sdownstreamand 48,000 bit/supstream.A lower bit rate may be chosen during the connection establishment phase due toadaptive modulation– slower but more robust modulation schemes are chosen in case of poorsignal-to-noise ratio.Due to data compression, the actual data transmission rate or throughput (see below) may be higher.

Thechannel capacity,also known as theShannoncapacity, 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-nodecommunication link.

net bit rate ≤ channel capacity

The channel capacity is proportional to theanalog bandwidthin hertz. This proportionality is calledHartley's law.Consequently, the net bit rate is sometimes calleddigital bandwidthcapacity in bit/s.

Network throughput

Main article:Network throughput

The termthroughput,essentially the same thing asdigital bandwidthconsumption,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 alsomeasuring network throughput.

Goodput (data transfer rate)

Main article:Goodput

Goodputordata transfer raterefers to the achieved average net bit rate that is delivered to theapplication layer,exclusive of all protocol overhead, data packets retransmissions, etc. For example, in the case of file transfer, the goodput corresponds to the achievedfile transfer rate.The file transfer rate in bit/s can be calculated as the file size (in bytes) divided by the file transfer time (in seconds) and multiplied by eight.

As an example, the goodput or data transfer rate of a V.92 voiceband modem is affected by the modem physical layer and data link layer protocols. It is sometimes higher than the physical layer data rate due toV.44data compression,and sometimes lower due to bit-errors andautomatic repeat requestretransmissions.

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

goodput ≤ throughput ≤ maximum throughput ≤ net bit rate

for a certain communication path.

Progress trends

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

WANmodems	EthernetLAN	WiFiWLAN	Mobile data
1972:Acoustic coupler300 baud 1977: 1200 baudVadic and Bell 212A 1986:ISDNintroduced with two 64 kbit/s channels (144 kbit/s gross bit rate) 1990:V.32bismodems:2400 / 4800 / 9600 / 19200 bit/s 1994:V.34modems with 28.8 kbit/s 1995:V.90modems with 56 kbit/s downstreams, 33.6 kbit/s upstreams 1999:V.92modems with 56 kbit/s downstreams, 48 kbit/s upstreams 1998:ADSL(ITU G.992.1) up to 10 Mbit/s 2003:ADSL2(ITU G.992.3) up to 12 Mbit/s 2005:ADSL2+(ITU G.992.5) up to 26 Mbit/s 2005:VDSL2(ITU G.993.2) up to 200 Mbit/s 2014:G.fast(ITU G.9701) up to 1000 Mbit/s	1975: Experimental 2.94 Mbit/s 1981: 10 Mbit/s10BASE5(coaxial cable) 1990: 10 Mbit/s10BASE-T(twisted pair) 1995: 100 Mbit/sFast Ethernet 1999:Gigabit Ethernet 2003:10 Gigabit Ethernet 2010:100 Gigabit Ethernet 2017:200/400 Gigabit Ethernet	1997:802.112 Mbit/s 1999:802.11b11 Mbit/s 1999:802.11a54 Mbit/s 2003:802.11g54 Mbit/s 2007:802.11n600 Mbit/s 2012:802.11ac~1000 Mbit/s	1G: 1981:NMT1200 bit/s 2G: 1991:GSMCSDandD-AMPS14.4 kbit/s 2003:GSM EDGE296 kbit/s down, 118.4 kbit/s up 3G: 2001:UMTS-FDD (WCDMA) 384 kbit/s 2007: UMTSHSDPA14.4 Mbit/s 2008: UMTSHSPA14.4 Mbit/s down, 5.76 Mbit/s up 2009:HSPA+(WithoutMIMO) 28 Mbit/s downstreams (56 Mbit/s with 2×2 MIMO), 22 Mbit/s upstreams 2010: CDMA2000EV-DORev. B 14.7 Mbit/s downstreams 2011:HSPA+accelerated (With MIMO) 42 Mbit/s downstreams Pre-4G: 2007:Mobile WiMAX(IEEE 802.16e) 144 Mbit/s down, 35 Mbit/s up 2009:LTE100 Mbit/s downstreams (360 Mbit/s with MIMO 2×2), 50 Mbit/s upstreams 5G See also:comparison of mobile phone standards

For more examples, seelist of interface bit rates,spectral efficiency comparison table,andOFDM system comparison table.

Multimedia

In digital multimedia, bit rate represents the amount of information, or detail, that is stored per unit of time of a recording. The bitrate depends on several factors:

• The original material may be sampled at different frequencies.
• The samples may use different numbers of bits.
• The data may be encoded by different schemes.
• The information may be digitallycompressedby different algorithms or to different degrees.

Generally, choices are made about the above factors in order to achieve the desired trade-off between minimizing the bitrate and maximizing the quality of the material when it is played.

Iflossy data compressionis 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 ofcompression 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.

The encoding bit rate of a multimedia file is its size inbytesdivided by the playback time of the recording (in seconds), multiplied by eight.

For real-timestreaming multimedia,the encoding bit rate is thegoodputthat is required to avoid playback interruption.

The termaverage bitrateis used in case ofvariable bitratemultimedia source coding schemes. In this context, thepeak bit rateis the maximum number of bits required for any short-term block of compressed data.

A theoretical lower bound for the encoding bit rate forlossless data compressionis thesource information rate,also known as theentropy rate.

The bitrates in this section are approximately theminimumthat theaveragelistener in a typical listening or viewing environment, when using the best available compression, would perceive as not significantly worse than the reference standard.

Audio

CD-DA

Compact Disc Digital Audio(CD-DA) uses 44,100 samples per second, each with a bit depth of 16, a format sometimes abbreviated like "16bit / 44.1kHz". CD-DA is alsostereo,using a left and rightchannel,so the amount of audio data per second is double that of mono, where only a single channel is used.

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

${\text{bit rate}}={\text{sample rate}}\times {\text{bit depth}}\times {\text{channels}}$

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

$44,100\times 16\times 2=1,411,200\ {\text{bit/s}}=1,411.2\ {\text{kbit/s}}$

The cumulative size of a length of PCM audio data (excluding a fileheaderor othermetadata) can be calculated using the following formula:

${\text{size in bits}}={\text{sample rate}}\times {\text{bit depth}}\times {\text{channels}}\times {\text{time}}.$

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:

${\text{size in bytes}}={\frac {\text{size in bits}}{8}}$

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

${\frac {44,100\times 16\times 2\times 4,800}{8}}=846,720,000\ {\text{bytes}}\approx 847\ {\text{MB}}\approx 807.5\ {\text{MiB}}$

whereMiBis mebibytes withbinary prefixMi, meaning 2²⁰= 1,048,576.

MP3

TheMP3audio format provideslossy data compression.Audio quality improves with increasing bitrate:

• 32 kbit/s – generally acceptable only for speech
• 96 kbit/s – generally used for speech or low-quality streaming
• 128 or 160 kbit/s – mid-range bitrate quality
• 192 kbit/s – medium quality bitrate
• 256 kbit/s – a commonly used high-quality bitrate
• 320 kbit/s – highest level supported by theMP3standard

Other audio

• 700 bit/s – lowest bitrate open-source speech codecCodec2,but Codec2 sounds much better at 1.2 kbit/s
• 800 bit/s – minimum necessary for recognizable speech, using the special-purposeFS-1015speech codecs
• 2.15 kbit/s – minimum bitrate available through the open-sourceSpeexcodec
• 6 kbit/s – minimum bitrate available through the open-sourceOpuscodec
• 8 kbit/s –telephonequality using speech codecs
• 32–500 kbit/s –lossy audioas used inOgg Vorbis
• 256 kbit/s – Digital Audio Broadcasting (DAB)MP2bit rate required to achieve a high quality signal
• 292 kbit/s – SonyAdaptive Transform Acoustic Coding(ATRAC) for use on theMiniDisc Format
• 400 kbit/s–1,411 kbit/s –lossless audioas used in formats such asFree Lossless Audio Codec,WavPack,orMonkey's Audioto compress CD audio
• 1,411.2 kbit/s –Linear PCMsound format ofCD-DA
• 5,644.8 kbit/s –DSD,which is a trademarked implementation ofPDMsound format used onSuper Audio CD.
• 6.144 Mbit/s – E-AC-3 (Dolby Digital Plus), an enhanced coding system based on the AC-3 codec
• 9.6 Mbit/s –DVD-Audio,a digital format for delivering high-fidelity audio content on a DVD. DVD-Audio is not intended to be a video delivery format and is not the same as video DVDs containing concert films or music videos. These discs cannot be played on a standard DVD-player without DVD-Audio logo.
• 18 Mbit/s – advanced lossless audio codec based onMeridian Lossless Packing(MLP)

Video

• 16 kbit/s –videophonequality (minimum necessary for a consumer-acceptable "talking head" picture using various video compression schemes)
• 128–384 kbit/s – business-orientedvideoconferencingquality using video compression
• 400 kbit/sYouTube240p videos (usingH.264)
• 750 kbit/sYouTube360p videos (usingH.264)
• 1 Mbit/sYouTube480p videos (usingH.264)
• 1.15 Mbit/s max –VCDquality (usingMPEG1compression)
• 2.5 Mbit/sYouTube720p videos (usingH.264)
• 3.5 Mbit/s typ–Standard-definition televisionquality (with bit-rate reduction from MPEG-2 compression)
• 3.8 Mbit/sYouTube720p60 (60FPS) videos (using H.264)
• 4.5 Mbit/sYouTube1080p videos (usingH.264)
• 6.8 Mbit/sYouTube1080p60 (60FPS) videos (using H.264)
• 9.8 Mbit/s max –DVD(usingMPEG2compression)
• 8 to 15 Mbit/s typ –HDTVquality (with bit-rate reduction from MPEG-4 AVC compression)
• 19 Mbit/s approximate –HDV720p (using MPEG2 compression)
• 24 Mbit/s max –AVCHD(usingMPEG4 AVCcompression)
• 25 Mbit/s approximate –HDV1080i (using MPEG2 compression)
• 29.4 Mbit/s max –HD DVD
• 40 Mbit/s max –1080pBlu-ray Disc(using MPEG2, MPEG4 AVC orVC-1compression)
• 250 Mbit/s max –DCP(using JPEG 2000 compression)
• 1.4 Gbit/s – 10-bit4:4:4uncompressed 1080p at 24 FPS

Notes

For technical reasons (hardware/software protocols, overheads, encoding schemes, etc.) theactualbit rates used by some of the compared-to devices may be significantly higher than what is listed above. For example, telephone circuits usingμlaworA-lawcompanding(pulse code modulation) yield 64 kbit/s.

See also

• Audio bit depth
• Average bitrate
• Bandwidth (computing)
• Baud(symbol rate)
• Bit-synchronous operation
• Chip rate
• Clock rate
• Code rate
• Constant bitrate
• Data-rate units
• Data signaling rate
• List of interface bit rates
• Measuring network throughput
• Orders of magnitude (bit rate)
• Spectral efficiency
• Variable bitrate

External links

• Live Video Streaming Bitrate CalculatorCalculate bitrate for video and live streams
• DVD-HQ bit rate calculatorCalculate bit rate for various types of digital video media.
• Maximum PC - Do Higher MP3 Bit Rates Pay Off?
• Valid8 Data Rate Calculator