
Although it is widely used as a measure of the loudness of sound, the decibel is more generally a measure of the ratio between two quantities, and can be used to express a wide variety of measurements in acoustics and electronics. The decibel is in fact a "dimensionless unit" like percent. ===Definition=== The ratio between two power (physics) values and in decibels is given by the formula: Usually, is the quantity being measured and is a ''reference'' level. Where the ratio is between two field (physics) strength or voltage values (so that the power being transmitted is Proportionality (mathematics) the Square (algebra) of this value), the formula is: It can therefore be seen that a ratio expressed in decibels is independent of whether the measurements are made as field strength or power values. ===Standards=== The decibel is not an SI unit, although the Bureau International des Poids et Mesures (BIPM) has recommended its inclusion in the SI system. The d is therefore lowercase, as it is the SI prefix ''deci-'', and the B is capitalized, as it is an abbreviation of a name-derived unit, the ''bel'', named for Alexander Graham Bell. Written out it becomes ''decibel''. This is standard English language capitalization. ===Merits=== The use of decibels has three different merits: * It is convenient to add the decibel values e.g. of two subsequent amplifiers rather than to multiply their amplification factors. * A very large range of ratios can be expressed with decibel values in a range of moderate size, allowing e.g. to clearly visualize huge changes of some quantity. * In acoustics, the decibel as a logarithmic measure of ratios fits well to the logarithmic dependence of perceived loudness on sound intensity. == History of bels and decibels == A bel (symbol B) is a unit of measure of ratios, such as power (physics) levels and voltage levels. It is mostly used in telecommunication, electronics, and acoustics. Invented by engineers of the Bell Labs, it was originally called the ''transmission unit'' or ''TU'', but was renamed in 1923 or 1924 in honor of the laboratory's founder and telecommunications pioneer Alexander Graham Bell. The bel was too large for everyday use, so the decibel (dB), equal to 0.1 B, became more commonly used. The neper is a similar unit which uses the natural logarithm. The Richter scale uses numbers expressed in bels as well, though this is implied by definition rather than explicitly stated. In spectrometry and optics, the absorbance unit used to measure optical density is equivalent to -1 B. == Uses == === Acoustics === The decibel unit is often used in acoustics to quantify sound levels relative to some 0 dB reference. The reference may be defined as a sound pressure level (SPL), commonly 20 micropascals (20 μPa). To avoid confusion with other decibel measures, the term dB(SPL) is used for this. The reference sound pressure (corresponding to a sound pressure level of 0 dB) can also be defined as the sound pressure at the threshold of human Hearing (sense), which is conventionally taken to be 2×10−5 newton per square metre, 2×10−5 N/m² or 20 micropascals. That is roughly the sound of a mosquito flying 3 m away. The ears are only sensitive to sound pressure deviations. The reason for using the decibel is that the ear is capable of detecting a very large range of sound pressures. The ratio of the sound ''pressure'' that causes permanent damage from short exposure to the limit that (undamaged) ears can hear is more than a million. Because the ''power'' in a sound wave is proportional to the square of the pressure, the ratio of the maximum power to the minimum power is more than one (short scale) trillion. To deal with such a range, logarithmic units are useful: the log of a trillion is 12, so this ratio represents a difference of 120 dB. Psychologists have found that our perception of loudness is roughly logarithmic — see the Weber-Fechner Law. In other words, you have to multiply the sound pressure by the same factor to have the same increase in loudness. This is why the numbers around the volume control dial on a typical Electronic amplifier are related not to the voltage amplification, but to its logarithm. Various frequency weightings are used to allow the result of an acoustical measurement to be expressed as a single sound level. The weightings approximate the changes in sensitivity of the ear to different frequencies at different levels. The two most commonly used weightings are the A and C weightings; other examples are the B and Z weightings. Sound levels above 85 dB are considered harmful, while 120 dB is unsafe and 150 dB causes physical damage to the human body. Windows break at about 163 dB. Jet airplanes cause A-weighted levels of about 133 dB at 33 m, or 100 dB at 170 m. Eardrums rupture at 190 dB to 198 dB. Shock waves and sonic booms cause levels of about 200 dB at 330 m. Sound levels of around 200 dB can cause death to humans and are generated near bomb explosions (e.g. 23 kg of Trinitrotoluene detonated 3 m away). The space shuttle generates levels of around 215 dB (or an A-weighted level of about 175 dB at a distance of 17 m). Even louder are nuclear bombs, earthquakes, tornadoes, hurricanes and volcanoes. Some other values: {| border="1" cellspacing="0" cellpading="2" |dBSPL||Source (with distance!) |- |180||Rocket engine at 30 m |- |150||Jet engine at 30 m |- |130||Threshold of pain |- |120||Rock and roll concert; jet aircraft taking off at 100 m |- |110||Accelerating motorcycle at 5 m; chainsaw at 1 m |- |100||Jackhammer at 2 m; inside disco |- |90||Loud factory, heavy truck at 1 m |- |80||Vacuum cleaner at 1 m, curbside of busy street |- |70||Busy traffic at 5 m |- |60||Office or restaurant inside |- |50||Quiet restaurant inside |- |40||Residential area at night |- |30||Theatre, no talking |- |20||Only Rustling of Leaf |- |10||Human breathing at 3 m |- |0||Threshold of hearing (human with good ears) |} Under controlled conditions, in an acoustical laboratory, the trained healthy human ear is able to discern changes in sound levels of 1 dB, when exposed to steady, single frequency ("pure tone") signals in the mid-frequency range. It is widely accepted that the average healthy ear, however, can barely perceive noise level changes of 3 dB. On this scale, the normal range of human hearing extends from about 0 dB to about 140 dB. 0 dB is the threshold of hearing in healthy, undamaged human ears; 0 dB is not an absence of sound, and it is possible for people with exceptionally good hearing to hear sounds at -10 dB. A 3 dB increase in the level of continuous noise doubles the sound power, however experimentation has determined that the frequency response of the human ear results in a perceived doubling of loudness with every 10 dB increase; a 5 dB increase is a readily noticeable change, while a 3 dB increase is barely noticeable to most people. Sound pressure levels are applicable to the specific position at which they are measured. The levels change with the distance from the source of the sound; in general, the level decreases as the distance from the source increases. If the distance from the source is unknown, it is difficult to estimate the sound pressure level at the source. ==== Frequency weighting ==== Since the human ear is not equally sensitive to all the frequencies of sound within the entire spectrum, noise levels at maximum human sensitivity — middle A and its higher harmonics (between 2,000 and 4,000 hertz) — are factored more heavily into sound descriptions using a process called frequency weighting. The most widely used frequency weighting is the "A-weighting", which roughly corresponds to the inverse of the 40 dB (at 1 kHz) equal-loudness curve. Using this filter, the sound level Measuring instrument is less sensitive to very high and very low frequencies. The A weighting parallels the sensitivity of the human ear when it is exposed to normal levels, and frequency weighting C is suitable for use when the ear is exposed to higher sound levels. Other defined frequency weightings, such as B and Z, are rarely used. Frequency weighted sound levels are still expressed in decibels (with unit symbol dB), although it is common to see the incorrect unit symbols dBA or dB(A) used for A-weighted sound levels. === Electronics === The decibel is used rather than Arithmetic ratios or percentages because when certain types of Electrical network, such as amplifiers and attenuators, are connected in series, expressions of power level in decibels may be arithmetically added and subtracted. It is also common in disciplines such as audio, in which the properties of the signal are best expressed in logarithms due to the response of the ear. In radio electronics, the decibel is used to describe the ratio between two measurements of electrical power. It can also be combined with a suffix to create an absolute unit of electrical power. For example, it can be combined with "m" for "milliwatt" to produce the "dBm". Zero dBm is one milliwatt, and 1 dBm is one decibel greater than 0 dBm, or about 1.259 mW. Although decibels were originally used for power ratios, they are nowadays commonly used in electronics to describe voltage or current ratios. In a constant resistive load, power is proportional to the square of the voltage or current in the circuit. Therefore, the decibel ratio of two voltages ''V''1 and ''V''2 is defined as 20 log10(''V''1/''V''2), and similarly for current ratios. Thus, for example, a factor of 2.0 in voltage is equivalent to 6.02 dB (not 3.01 dB!). This practice is fully consistent with power-based decibels, provided the circuit Electrical resistance remains constant. However, voltage-based decibels are frequently used to express such quantities as the voltage gain of an amplifier, where the two voltages are measured in different circuits which may have very different resistances. For example, a unity-gain buffer amplifier with a high input resistance and a low output resistance may be said to have a "voltage gain of 0 dB", even though it is actually providing a considerable power gain when driving a low-resistance load. In professional audio, a popular unit is the dBu (see below for all the units). The "u" stands for "unloaded", and was probably chosen to be similar to lowercase "v", as dBv was the older name for the same thing. It was changed to avoid confusion with dBV. This unit (dBv) is an RMS measurement of voltage which uses as its reference 0.775 VRMS. Chosen for historical reasons, it is the voltage level at which you get 1 mW of power in a 600 ohm resistor, which used to be the standard impedance in almost all professional audio circuits. Since there may be many different bases for a measurement expressed in decibels, a dB value is meaningless unless the reference value (equivalent to 0 dB) is clearly stated. For example, the gain of an antenna system can only be given with respect to a reference antenna; if the reference is not stated, the dB gain value is not useable. === Optics === In an optical link, if a known amount of Optics power, in dBm (referenced to 1 mW), is launched into a Optical fiber, and the losses, in dB (decibels), of each component (e.g. connectors, splices, and lengths of fibre) are known, the overall link loss may be quickly calculated by simple addition and subtraction of decibel quantities. === Telecommunications === In telecommunications, decibels are commonly used to measure signal-to-noise ratios and other ratio measurements. === Seismology === Earthquakes are measured on the Richter magnitude scale, which is expressed in bels. (The units in this case are always assumed, rather than explicit.) == Typical abbreviations == === Absolute measurements === ==== Electric power ==== ; dBm ''or'' dBmW : dB(1 mW@600 Ω) — in analog signal audio, power measurement relative to 1 milliwatt into a 600 ohm load ; dBW : dB(1 W@600 Ω) — same as dBm, with reference level of 1 watt. ==== Electric voltage ==== ; dBu ''or'' dBv : dB(0.775 V) — (usually root mean square) voltage amplitude referenced to 0.775 volts, not related to any impedance. dBu is preferable, since dBv is easily confused with dBV. The "u" comes from "unloaded". ; dBV : dB(1 V) — (usually RMS) voltage amplitude of an audio signal in a wire, relative to 1 volt, not related to any impedance. ==== Acoustics ==== ; dB(SPL) : dB(Sound Pressure Level) — relative to 20 micropascals (μPa) = 2×10-5 Pa, the quietest sound a human can hear. This is roughly the sound of a mosquito flying 3 metres away. This is often abbreviated to just "dB", which gives some the erroneous notion that a dB is an absolute unit by itself. ==== Radio power ==== ; dBm : dB(mW) — power relative to 1 milliwatt. ; dBμ ''or'' dBu : dB(μV/m) — electric field strength relative to 1 microvolt per metre. ; dBf : dB(fW) — power relative to 1 femtowatt. ; dBW : dB(W) — power relative to 1 watt. ; dBk : dB(kW) — power relative to 1 kilowatt. === Relative measurements === ; dB(A) weighting : These symbols are often used to denote the use of different frequency weightings, used to approximate the human ear's response to sound, although the measurement is still in dB (SPL). Other variations that may be seen are dBA or dBA. According to ANSI standards, the preferred usage is to write LA = x dB, as dBA implies a reference to an "A" unit, not an A-weighting. They are still used commonly as a shorthand for A-weighted measurements, however. ; dBd : dB(dipole) — the forward gain of an antenna (electronics) compared to a half-wave dipole antenna. ; dBi : dB(isotropic) — the forward gain of an antenna compared to an imaginary isotropic antenna. ; dBFS ''or'' dBfs : dB(full scale) — the amplitude of a signal (usually audio) compared to the maximum which a device can handle before clipping occurs. In digital systems, 0 dBFS would equal the highest level (number) the processor is capable of representing. (Measured values are negative, since they are less than the maximum.) ; dBr : dB(relative) — simply a relative difference to something else, which is made apparent in context. The difference of a filter's response to nominal levels, for instance. ; dBrn : dB above reference noise. == Reckoning == Decibels are handy for mental calculation, because adding them is easier than multiplying ratios. First, however, one has to be able to convert easily between ratios and decibels. The most obvious way is to memorize the logs of small primes, but there are a few other tricks that can help. === The 4 → 6 energy rule === To one decimal place of precision, 4.x is 6.x in dB (energy). Examples: * 4.0 → 6.0 dB * 4.3 → 6.3 dB * 4.7 → 6.7 dB === The "789" rule === To one decimal place of precision, x → (½ x + 5.0 dB) for 7.0 ≤ x ≤ 10. Examples: * 7.0 → ½ 7.0 + 5.0 dB = 3.5 + 5.0 dB = 8.5 dB * 7.5 → ½ 7.5 + 5.0 dB = 3.75 + 5.0 dB = 8.75 dB * 8.2 → ½ 8.2 + 5.0 dB = 4.1 + 5.0 dB = 9.1 dB * 9.9 → ½ 9.9 + 5.0 dB = 4.95 + 5.0 dB = 9.95 dB * 10.0 → ½ 10.0 + 5.0 dB = 5.0 + 5.0 dB = 10 dB === −3 dB = ½ power === A level difference of ±3 dB is roughly double/half power (equal to a ratio of 1.995). That is why it is commonly used as a marking on sound equipment and the like. Another common sequence is 1, 2, 5, 10, 20, 50 ... . These numbers are very close to being equally spaced in terms of their logarithms. The actual values would be 1, 2.15, 4.64, 10 ... . The conversion for decibels is often simplified to: "+3 dB means two times the power and 1.414 times the voltage", and "+6 dB means four times the power and two times the voltage ". While this is accurate for many situations, it is not exact. As stated above, decibels are defined so that +10 dB means "ten times the power". From this, we calculate that +3 dB actually multiplies the power by 103/10. This is a power ratio of 1.9953 or about 0.25% different from the "times 2" power ratio that is sometimes assumed. A level difference of +6 dB is 3.9811, about 0.5% different from 4. To contrive a more serious example, consider converting a large decibel figure into its linear ratio, for example 120 dB. The power ratio is correctly calculated as a ratio of 1012 or one trillion. But if we use the assumption that 3 dB means "times 2", we would calculate a power ratio of 2120/3 = 240 = 1.0995 × 1012, for a 10% error. ===6 dB per bit=== In digital audio, each bit offered by the system doubles the (voltage) resolution, corresponding to a 6 dB ratio. For instance, a 16-bit (linear) audio format offers a theoretical maximum of (16 x 6) = 96 dB, meaning that the maximum signal (see ''0dBFS'', above) is 96 dB above the quantization noise. == See also == *Noise *Sound pressure level == External links == *[http://www.phys.unsw.edu.au/~jw/dB.html What is a dB?] *[http://www.sizes.com/units/decibel.htm Description of some abbreviations] *[http://www.uoguelph.ca/HR/ehs/policies/10-01.pdf Noise Control and Hearing Conservation] *[http://www.osha.gov/dts/osta/otm/otm_iii/otm_iii_5.html Noise Measurement OSHA 1] *[http://www.environmental-center.com/articles/article138/article138.htm Noise Measurement OSHA 2] *[http://www.jimprice.com/prosound/db.htm Understanding dB] *[http://www.rane.com/par-d.html#decibel Rane Professional Audio Reference entry for "decibel"] *[http://hyperphysics.phy-astr.gsu.edu/hbase/sound/db.html#c1 Hyperphysics description of decibels] === Converters === *[http://www.analog.com/Analog_Root/static/techSupport/designTools/interactiveTools/dbconvert/dbconvert.html Vpeak, VRMS, Power, dBm, dBu, dBV converter] *[http://www.sengpielaudio.com/calculator-db-volt.htm Conversion: dBu to volts, dBV to volts, and volts to dBu, and dBV] *[http://www.sengpielaudio.com/calculator-soundlevel.htm Conversion of sound level units: dBSPL or dBA to sound pressure p and sound intensity J] *[http://www.sengpielaudio.com/calculator-volt.htm Conversion: Voltage V to dB, dBu, dBV, and dBm] *[http://www.moonblinkwifi.com/dbm_to_watt_conversion.cfm Strange dBm to mW conversion] ==Reference== *Martin, W. H., "DeciBel – The New Name for the Transmission Unit", ''Bell System Technical Journal'', January 1929. Units of measure Sound Acoustics
== Bel vs. Decibel, which came first? == The part until the next line has been moved over from Talk:Decibel: Earlier I thought Alexander Graham Bell coined the term "bel" as a measurement of sound and that it was later determined to be so coarse that 1/10th of it proved more useful (the decibel). On seeing someone on this page claim that Bell coined the phrase "decibel" I looked up its history in the Oxford English Dictionary. The OED has their earliest recorded uses in 1928 and 1929; Bell died in 1922. *the earliest few quotations the OED has on file for "decibel": ''"1928 Electrical Communication VII. I. 33/2 If common logarithms are used, the reproduction is obtained in Decibels. 1929 W. H. MARTIN in Bell System Techn. Jrnl. VIII. 2 The Bell System has adopted the name ?decibel? for the ?transmission unit?, based on a power ratio of 10·1... For convenience, the symbol ?db? will be employed to indicate the name ?decibel?. 1930 Discovery Dec. 398/2 The band-pass filter, which follows the low frequency modulator, allows the lower side-band to pass with an attenuation of six decibels."'' *the earliest few quotations the OED has on file for "bel": ''"1929 W. H. MARTIN in Bell System Techn. Jrnl. VIII. 2 It was further suggested that the naperian unit be called the ?neper? and that the fundamental decimal unit be called the ?bel?, these names being derived from..Napier..and Alexander Graham Bell. 1930 Gloss. Terms Electr. Engin. (B.S.I.) 13 The bel is a unit used in the comparison of the magnitudes of power, voltages or currents at two different points in a network of lines or apparatus."'' Clearly the term "bel" was in use before the term for 1/10th of it came about. Yet it seems odd to me that the terms did not see print for almost a decade. Anyone? Specifically, I'd like to know who made the suggestion for the terms "napier" and "bel." I suspect it wasn't Alexander Graham Bell. --user:Koyaanis Qatsi I've generalised the article a bit, since decibels are not just used for acoustics (e.g. they're used to measure the gain of amplifiers and loss of transmission lines.) -- DrBob == Acoustic decibel reference == How likely is it, if I find a claim that a sound is at, say, 120dB, that the reference level is indeed 20 micropascals? Similarly, if author A claims that one sound is so many dB, and author B claims that one sound is so many dB, how safe is it to compare the measures given, if neither indicates the reference level? --User:Ryguasu 04:38 Feb 26, 2003 (UTC) == Watts vs watts per square meter == This 0 (zero), decibel level also corresponds to one billionth of a watt, 0.000 000 000 001 watt, roughly a mosquito flying 10 feet away. :Watt would be total power, not related to distance; also http://ccms.ntu.edu.tw/~karchung/decibels/decibels1.ppt says 40 dB. - User:Patrick 09:52 Apr 16, 2003 (UTC) == List of acoustic decibel levels == It'd be nice to have a list of example decibel levels on this article - User:Khendon == Decibel vs Bel, separate article for acoustics or not == # Do acoustic decibels and general decibels really need to be separate articles? # Since decibel is much more commonly used than bel, shouldn't it be the title of the article? kind of like kilogram being the standard SI unit, even though it is a basic unit with a prefix. - User:Omegatron 00:47, Apr 17, 2004 (UTC) :Agreed Omegatron, I think this article should move to decibel - anyone disagree? -- User:Rissa of the saiya-jin 00:45, 6 Jun 2004 (UTC) ::I am moving it back to decibel. It is much more common. it sounds like the richter scale uses bels without calling it as such, but EVERYTHING else uses decibels. - User:Omegatron 14:12, Jun 27, 2004 (UTC) == 20 micropascals or 2 pascals??? == This seems to say that dB SPL is referenced to both 20 micropascals and 2 pascals. I'm sure the standard (used for dBA, etc.) is only one of those. Which is it? - User:Omegatron 17:43, Nov 23, 2004 (UTC) :20 micro. someone put in 2 N/m^2 without any exponent for some reason. fixed now. - User:Omegatron 17:51, Nov 23, 2004 (UTC) == which dB? == Please make sure the reference for all values listed as only dB are clear from context. (dB SPL, dBu, etc.) - User:Omegatron 17:43, Nov 23, 2004 (UTC) == Theatre? == One of the values in the table is "Theatre". That's too vague to be at all useful (to me, at least). An empty theatre? A filled theatre of whispering people? Sitting 5m away from Hamlet giving his soliloquy? A theatre showing a Jerry Bruckheimer movie? (From context, probably not the last one, but that's still a decent range.) ==Kerbside vs Curbside== The original spelling in this article was by Heron on 18 Nov as Kerbside. This is fine. Unless you wish to remove the entire entry, please leave the spelling in its original sense. User:Icairns 00:29, 8 Dec 2004 (UTC) :Not that it's terribly important, but the policy seems to be one of consistency for the whole page: :* Wikipedia:How_to_copyedit#Correcting_spelling :* Wikipedia:Tutorial_(Keep_in_mind)#U.S._English_vs._British_English :- User:Omegatron 15:19, Dec 8, 2004 (UTC) == dBA incorrect? == according to whom? - User:Omegatron 02:57, Dec 12, 2004 (UTC) :Exactly my question. The link is to dB(A), and that's what I've seen the manufacturers use ([http://www.electrolux.com/node507.asp]).--User:Jerryseinfeld 18:38, 23 Jan 2005 (UTC) ::Well yeah, manufacturers use it all the time (not just "historical sources"). Someone is claiming that it's not official, though, because it implies a reference to an "A" unit, like dBV implies a reference to a volt. Either this is a small minority opinion, or it's a new opinion that just hasn't gained a foothold yet, like binary prefixes like "mebibyte". My personal opinion is that it's fine to use it the way it is. It's just a shorthand way of saying it's A-weighted. Like saying miles (survey). In addition, the standard acoustic version is just "dB" with ''no'' qualifier (it should be dB SPL or dBSPL or dB(SPL)) which leads laymen to believe that a dB is a unit by itself. I would much rather see people using dB SPL than see them stop using dB (A). - User:Omegatron 20:08, Jan 23, 2005 (UTC) === Unit symbol dB rather than dBA, dB(A) etc === When making acoustical measurements and determining, for example, an A-weighted sound pressure level, the measured sound pressure is still compared with the reference sound pressure (20 μPa), and the unit symbol should still be dB. This is standard usage in definitions given in modern ISO and IEC standards, and is now mandated for ANSI standards developed by the Acoustical Society of America in their ASACOS rules. The preferred form of expression is "the A-weighted sound level was xx dB" or ''L''A = xx dB. There are many historical sources which use "dBA", or "dB(A)" or talk about "dBA levels", and these should be understood as indicating A-weighted sound levels, although the unit symbol is incorrect. Unit symbols such as dBu or dBm indicate the reference value used to determine the level, and thus are correct. But the A denotes a frequency weighting, not a reference quantity. == Potential inclusion in SI == Any citation to support the claim that "(BIPM) has recommended its inclusion in the SI system."? *This doesn't even seem plausible to me—it's outside BIPM's bailiwick. More likely the Comité International des Poids et Mesures (CIPM), or the Consultative Committee on Units which is, I think, under the CIPM and advises the CGPM Also, does that recommendation include the neper as well as the decibel? User:Gene Nygaard 01:51, 19 Jan 2005 (UTC) == RMS == "dB(0.775 V)—(usually RMS) voltage amplitude" :Is it ''ever'' not RMS? Every site I see says it is referenced to RMS. - User:Omegatron 02:50, Jan 19, 2005 (UTC) == Is this website violating the GNU License?? == http://encyclopedia.laborlawtalk.com/Decibel if so, i find it funny that a "law" site is guilty of copyright violation. : No, it does not appear so. User:203.26.206.129 07:09, 13 Apr 2005 (UTC) : Read the bottom of the page: "This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Decibel"." User:RoceKiller 10:16, 14 Apr 2005 (UTC) == dB Doubling Versus "Perceived" Doubling == So I always thought that 10dB represented a doubling of the sound intensity but now I find out that this may be technically incorrect. That 3dB represents a true doubling of sound pressure and that 10dB is where the human ear ''perceives'' the pressure as doubling. Can anyone confirm this? It would be nice for the article to clarify this. :I'm not sure of the actual answer, but these are where you should look. I'm going to try to figure it out, too: 3.01 dB corresponds to a doubling of sound power, not sound pressure. How we perceive it depends on amplitude and frequency, and would be derived from the equal-loudness contour. Also see the units of perceived loudness, phon and sone. - User:Omegatron 16:36, Apr 29, 2005 (UTC) :Wow. You helped me realize there are a lot of confusing, overlapping sound measurement articles. I've created a template to keep them tied together: Template:Sound measurements - User:Omegatron 16:49, Apr 29, 2005 (UTC) == Amplitude vs power == I'm still sketchy on the relationship between power and amplitude and dB. You can't convert from a power to a dB to a voltage, for instance, unless you know a load resistance. I'm especially confused because you can't convert amplitude --> dBFS --> power in digital land which doesn't even have load resistance. What does "power" even mean for digital?? - User:Omegatron 20:13, Apr 29, 2005 (UTC) YEEARG - and I had explicitly edited this article to correct this, and it has been reverted. decibels are DEFINED AS 10log10(x) - PERIOD. This 20log10 crap is WRONG! dB are NEVER 20log10 of ANYTHING. Now, when you are talking about dBWatts (or any derived units like dBmW) you can compute the CHANGE in level by computing 20log10(V1/V2), but that is a simplification of the full formula 10log10( (V1*V1/R)/(V2*V2/R) ). But it is also perfectly valid to speak of dBV - and a 10 dB increase of a 0dBv signal yeilds 10 volts, NOT 100! dB absent any unit is a RELATIVE measurement - I can speak of a 6dB increase of my bank account (a thing much to be desired), but I cannot speak of having 6dB in my bank account - I can say I have 36dB$ in the bank, but I *have* to supply a unit for an absolute measure to be meaningful. I design test equipment for a living, and this confusion causes us NO END of problems. People will increase the deivation of an FM signal by 2, and expect to see the audio spectrum analyzer increase by 6 dB. The spec-an is measuring deviation, so a x2 increase is 10log10(2) = 3dB. To get a 6dB increase we would have to be reporting (kHz deviation)^2 - now what physical property does that describe? Please - dB is 10log10(x) ALWAYS - not 20log10! Revert the reversion of my changes, please! N0YKG 10 May 2005 : Here's your chance to be bold and put the above explanation why 20 log 10(X/Xref) is wrong into the article. Though I admit I don't see why it's wrong to say 20 log ((V1/V2)) as opposed to 10 log((V1/V2)^2), assuming the circuit impedance is the same. dB should always be used to refer to ratios of power quantities, not to ratios of amplitude quantities...but we often cheat and say 20 log (amplitude/reference amplitude) --User:Wtshymanski 19:02, 10 May 2005 (UTC) :On the one hand, you say dB should only be used for power quantities, but then you say that dB could be used for your bank account. Also: :* 0 VRMS = 0 dBV :* 10 VRMS = 20 dBV :* 100 VRMS = 40 dBV :According to [http://www.analog.com/Analog_Root/static/techSupport/designTools/interactiveTools/dbconvert/dbconvert.html this], which claims to be based on the ANSI T1.523-2001 definitions, which I would download, except [https://www.atis.org/atis/docstore/doc_display.asp?ID=928 it costs $175] - User:Omegatron 20:21, May 10, 2005 (UTC)
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Decibel
Although it is widely used as a measure of the loudness of sound, the decibel is more generally a measure of the ratio between two quantities, and can be used to express a wide variety of measurements in acoustics and electronics. The decibel is in fact a "dimensionless unit" like percent. ===Definition=== The ratio between two power (physics) values and in decibels is given by the formula: Usually, is the quantity being measured and is a ''reference'' level. Where the ratio is between two field (physics) strength or voltage values (so that the power being transmitted is Proportionality (mathematics) the Square (algebra) of this value), the formula is: It can therefore be seen that a ratio expressed in decibels is independent of whether the measurements are made as field strength or power values. ===Standards=== The decibel is not an SI unit, although the Bureau International des Poids et Mesures (BIPM) has recommended its inclusion in the SI system. The d is therefore lowercase, as it is the SI prefix ''deci-'', and the B is capitalized, as it is an abbreviation of a name-derived unit, the ''bel'', named for Alexander Graham Bell. Written out it becomes ''decibel''. This is standard English language capitalization. ===Merits=== The use of decibels has three different merits: * It is convenient to add the decibel values e.g. of two subsequent amplifiers rather than to multiply their amplification factors. * A very large range of ratios can be expressed with decibel values in a range of moderate size, allowing e.g. to clearly visualize huge changes of some quantity. * In acoustics, the decibel as a logarithmic measure of ratios fits well to the logarithmic dependence of perceived loudness on sound intensity. == History of bels and decibels == A bel (symbol B) is a unit of measure of ratios, such as power (physics) levels and voltage levels. It is mostly used in telecommunication, electronics, and acoustics. Invented by engineers of the Bell Labs, it was originally called the ''transmission unit'' or ''TU'', but was renamed in 1923 or 1924 in honor of the laboratory's founder and telecommunications pioneer Alexander Graham Bell. The bel was too large for everyday use, so the decibel (dB), equal to 0.1 B, became more commonly used. The neper is a similar unit which uses the natural logarithm. The Richter scale uses numbers expressed in bels as well, though this is implied by definition rather than explicitly stated. In spectrometry and optics, the absorbance unit used to measure optical density is equivalent to -1 B. == Uses == === Acoustics === The decibel unit is often used in acoustics to quantify sound levels relative to some 0 dB reference. The reference may be defined as a sound pressure level (SPL), commonly 20 micropascals (20 μPa). To avoid confusion with other decibel measures, the term dB(SPL) is used for this. The reference sound pressure (corresponding to a sound pressure level of 0 dB) can also be defined as the sound pressure at the threshold of human Hearing (sense), which is conventionally taken to be 2×10−5 newton per square metre, 2×10−5 N/m² or 20 micropascals. That is roughly the sound of a mosquito flying 3 m away. The ears are only sensitive to sound pressure deviations. The reason for using the decibel is that the ear is capable of detecting a very large range of sound pressures. The ratio of the sound ''pressure'' that causes permanent damage from short exposure to the limit that (undamaged) ears can hear is more than a million. Because the ''power'' in a sound wave is proportional to the square of the pressure, the ratio of the maximum power to the minimum power is more than one (short scale) trillion. To deal with such a range, logarithmic units are useful: the log of a trillion is 12, so this ratio represents a difference of 120 dB. Psychologists have found that our perception of loudness is roughly logarithmic — see the Weber-Fechner Law. In other words, you have to multiply the sound pressure by the same factor to have the same increase in loudness. This is why the numbers around the volume control dial on a typical Electronic amplifier are related not to the voltage amplification, but to its logarithm. Various frequency weightings are used to allow the result of an acoustical measurement to be expressed as a single sound level. The weightings approximate the changes in sensitivity of the ear to different frequencies at different levels. The two most commonly used weightings are the A and C weightings; other examples are the B and Z weightings. Sound levels above 85 dB are considered harmful, while 120 dB is unsafe and 150 dB causes physical damage to the human body. Windows break at about 163 dB. Jet airplanes cause A-weighted levels of about 133 dB at 33 m, or 100 dB at 170 m. Eardrums rupture at 190 dB to 198 dB. Shock waves and sonic booms cause levels of about 200 dB at 330 m. Sound levels of around 200 dB can cause death to humans and are generated near bomb explosions (e.g. 23 kg of Trinitrotoluene detonated 3 m away). The space shuttle generates levels of around 215 dB (or an A-weighted level of about 175 dB at a distance of 17 m). Even louder are nuclear bombs, earthquakes, tornadoes, hurricanes and volcanoes. Some other values: {| border="1" cellspacing="0" cellpading="2" |dBSPL||Source (with distance!) |- |180||Rocket engine at 30 m |- |150||Jet engine at 30 m |- |130||Threshold of pain |- |120||Rock and roll concert; jet aircraft taking off at 100 m |- |110||Accelerating motorcycle at 5 m; chainsaw at 1 m |- |100||Jackhammer at 2 m; inside disco |- |90||Loud factory, heavy truck at 1 m |- |80||Vacuum cleaner at 1 m, curbside of busy street |- |70||Busy traffic at 5 m |- |60||Office or restaurant inside |- |50||Quiet restaurant inside |- |40||Residential area at night |- |30||Theatre, no talking |- |20||Only Rustling of Leaf |- |10||Human breathing at 3 m |- |0||Threshold of hearing (human with good ears) |} Under controlled conditions, in an acoustical laboratory, the trained healthy human ear is able to discern changes in sound levels of 1 dB, when exposed to steady, single frequency ("pure tone") signals in the mid-frequency range. It is widely accepted that the average healthy ear, however, can barely perceive noise level changes of 3 dB. On this scale, the normal range of human hearing extends from about 0 dB to about 140 dB. 0 dB is the threshold of hearing in healthy, undamaged human ears; 0 dB is not an absence of sound, and it is possible for people with exceptionally good hearing to hear sounds at -10 dB. A 3 dB increase in the level of continuous noise doubles the sound power, however experimentation has determined that the frequency response of the human ear results in a perceived doubling of loudness with every 10 dB increase; a 5 dB increase is a readily noticeable change, while a 3 dB increase is barely noticeable to most people. Sound pressure levels are applicable to the specific position at which they are measured. The levels change with the distance from the source of the sound; in general, the level decreases as the distance from the source increases. If the distance from the source is unknown, it is difficult to estimate the sound pressure level at the source. ==== Frequency weighting ==== Since the human ear is not equally sensitive to all the frequencies of sound within the entire spectrum, noise levels at maximum human sensitivity — middle A and its higher harmonics (between 2,000 and 4,000 hertz) — are factored more heavily into sound descriptions using a process called frequency weighting. The most widely used frequency weighting is the "A-weighting", which roughly corresponds to the inverse of the 40 dB (at 1 kHz) equal-loudness curve. Using this filter, the sound level Measuring instrument is less sensitive to very high and very low frequencies. The A weighting parallels the sensitivity of the human ear when it is exposed to normal levels, and frequency weighting C is suitable for use when the ear is exposed to higher sound levels. Other defined frequency weightings, such as B and Z, are rarely used. Frequency weighted sound levels are still expressed in decibels (with unit symbol dB), although it is common to see the incorrect unit symbols dBA or dB(A) used for A-weighted sound levels. === Electronics === The decibel is used rather than Arithmetic ratios or percentages because when certain types of Electrical network, such as amplifiers and attenuators, are connected in series, expressions of power level in decibels may be arithmetically added and subtracted. It is also common in disciplines such as audio, in which the properties of the signal are best expressed in logarithms due to the response of the ear. In radio electronics, the decibel is used to describe the ratio between two measurements of electrical power. It can also be combined with a suffix to create an absolute unit of electrical power. For example, it can be combined with "m" for "milliwatt" to produce the "dBm". Zero dBm is one milliwatt, and 1 dBm is one decibel greater than 0 dBm, or about 1.259 mW. Although decibels were originally used for power ratios, they are nowadays commonly used in electronics to describe voltage or current ratios. In a constant resistive load, power is proportional to the square of the voltage or current in the circuit. Therefore, the decibel ratio of two voltages ''V''1 and ''V''2 is defined as 20 log10(''V''1/''V''2), and similarly for current ratios. Thus, for example, a factor of 2.0 in voltage is equivalent to 6.02 dB (not 3.01 dB!). This practice is fully consistent with power-based decibels, provided the circuit Electrical resistance remains constant. However, voltage-based decibels are frequently used to express such quantities as the voltage gain of an amplifier, where the two voltages are measured in different circuits which may have very different resistances. For example, a unity-gain buffer amplifier with a high input resistance and a low output resistance may be said to have a "voltage gain of 0 dB", even though it is actually providing a considerable power gain when driving a low-resistance load. In professional audio, a popular unit is the dBu (see below for all the units). The "u" stands for "unloaded", and was probably chosen to be similar to lowercase "v", as dBv was the older name for the same thing. It was changed to avoid confusion with dBV. This unit (dBv) is an RMS measurement of voltage which uses as its reference 0.775 VRMS. Chosen for historical reasons, it is the voltage level at which you get 1 mW of power in a 600 ohm resistor, which used to be the standard impedance in almost all professional audio circuits. Since there may be many different bases for a measurement expressed in decibels, a dB value is meaningless unless the reference value (equivalent to 0 dB) is clearly stated. For example, the gain of an antenna system can only be given with respect to a reference antenna; if the reference is not stated, the dB gain value is not useable. === Optics === In an optical link, if a known amount of Optics power, in dBm (referenced to 1 mW), is launched into a Optical fiber, and the losses, in dB (decibels), of each component (e.g. connectors, splices, and lengths of fibre) are known, the overall link loss may be quickly calculated by simple addition and subtraction of decibel quantities. === Telecommunications === In telecommunications, decibels are commonly used to measure signal-to-noise ratios and other ratio measurements. === Seismology === Earthquakes are measured on the Richter magnitude scale, which is expressed in bels. (The units in this case are always assumed, rather than explicit.) == Typical abbreviations == === Absolute measurements === ==== Electric power ==== ; dBm ''or'' dBmW : dB(1 mW@600 Ω) — in analog signal audio, power measurement relative to 1 milliwatt into a 600 ohm load ; dBW : dB(1 W@600 Ω) — same as dBm, with reference level of 1 watt. ==== Electric voltage ==== ; dBu ''or'' dBv : dB(0.775 V) — (usually root mean square) voltage amplitude referenced to 0.775 volts, not related to any impedance. dBu is preferable, since dBv is easily confused with dBV. The "u" comes from "unloaded". ; dBV : dB(1 V) — (usually RMS) voltage amplitude of an audio signal in a wire, relative to 1 volt, not related to any impedance. ==== Acoustics ==== ; dB(SPL) : dB(Sound Pressure Level) — relative to 20 micropascals (μPa) = 2×10-5 Pa, the quietest sound a human can hear. This is roughly the sound of a mosquito flying 3 metres away. This is often abbreviated to just "dB", which gives some the erroneous notion that a dB is an absolute unit by itself. ==== Radio power ==== ; dBm : dB(mW) — power relative to 1 milliwatt. ; dBμ ''or'' dBu : dB(μV/m) — electric field strength relative to 1 microvolt per metre. ; dBf : dB(fW) — power relative to 1 femtowatt. ; dBW : dB(W) — power relative to 1 watt. ; dBk : dB(kW) — power relative to 1 kilowatt. === Relative measurements === ; dB(A) weighting : These symbols are often used to denote the use of different frequency weightings, used to approximate the human ear's response to sound, although the measurement is still in dB (SPL). Other variations that may be seen are dBA or dBA. According to ANSI standards, the preferred usage is to write LA = x dB, as dBA implies a reference to an "A" unit, not an A-weighting. They are still used commonly as a shorthand for A-weighted measurements, however. ; dBd : dB(dipole) — the forward gain of an antenna (electronics) compared to a half-wave dipole antenna. ; dBi : dB(isotropic) — the forward gain of an antenna compared to an imaginary isotropic antenna. ; dBFS ''or'' dBfs : dB(full scale) — the amplitude of a signal (usually audio) compared to the maximum which a device can handle before clipping occurs. In digital systems, 0 dBFS would equal the highest level (number) the processor is capable of representing. (Measured values are negative, since they are less than the maximum.) ; dBr : dB(relative) — simply a relative difference to something else, which is made apparent in context. The difference of a filter's response to nominal levels, for instance. ; dBrn : dB above reference noise. == Reckoning == Decibels are handy for mental calculation, because adding them is easier than multiplying ratios. First, however, one has to be able to convert easily between ratios and decibels. The most obvious way is to memorize the logs of small primes, but there are a few other tricks that can help. === The 4 → 6 energy rule === To one decimal place of precision, 4.x is 6.x in dB (energy). Examples: * 4.0 → 6.0 dB * 4.3 → 6.3 dB * 4.7 → 6.7 dB === The "789" rule === To one decimal place of precision, x → (½ x + 5.0 dB) for 7.0 ≤ x ≤ 10. Examples: * 7.0 → ½ 7.0 + 5.0 dB = 3.5 + 5.0 dB = 8.5 dB * 7.5 → ½ 7.5 + 5.0 dB = 3.75 + 5.0 dB = 8.75 dB * 8.2 → ½ 8.2 + 5.0 dB = 4.1 + 5.0 dB = 9.1 dB * 9.9 → ½ 9.9 + 5.0 dB = 4.95 + 5.0 dB = 9.95 dB * 10.0 → ½ 10.0 + 5.0 dB = 5.0 + 5.0 dB = 10 dB === −3 dB = ½ power === A level difference of ±3 dB is roughly double/half power (equal to a ratio of 1.995). That is why it is commonly used as a marking on sound equipment and the like. Another common sequence is 1, 2, 5, 10, 20, 50 ... . These numbers are very close to being equally spaced in terms of their logarithms. The actual values would be 1, 2.15, 4.64, 10 ... . The conversion for decibels is often simplified to: "+3 dB means two times the power and 1.414 times the voltage", and "+6 dB means four times the power and two times the voltage ". While this is accurate for many situations, it is not exact. As stated above, decibels are defined so that +10 dB means "ten times the power". From this, we calculate that +3 dB actually multiplies the power by 103/10. This is a power ratio of 1.9953 or about 0.25% different from the "times 2" power ratio that is sometimes assumed. A level difference of +6 dB is 3.9811, about 0.5% different from 4. To contrive a more serious example, consider converting a large decibel figure into its linear ratio, for example 120 dB. The power ratio is correctly calculated as a ratio of 1012 or one trillion. But if we use the assumption that 3 dB means "times 2", we would calculate a power ratio of 2120/3 = 240 = 1.0995 × 1012, for a 10% error. ===6 dB per bit=== In digital audio, each bit offered by the system doubles the (voltage) resolution, corresponding to a 6 dB ratio. For instance, a 16-bit (linear) audio format offers a theoretical maximum of (16 x 6) = 96 dB, meaning that the maximum signal (see ''0dBFS'', above) is 96 dB above the quantization noise. == See also == *Noise *Sound pressure level == External links == *[http://www.phys.unsw.edu.au/~jw/dB.html What is a dB?] *[http://www.sizes.com/units/decibel.htm Description of some abbreviations] *[http://www.uoguelph.ca/HR/ehs/policies/10-01.pdf Noise Control and Hearing Conservation] *[http://www.osha.gov/dts/osta/otm/otm_iii/otm_iii_5.html Noise Measurement OSHA 1] *[http://www.environmental-center.com/articles/article138/article138.htm Noise Measurement OSHA 2] *[http://www.jimprice.com/prosound/db.htm Understanding dB] *[http://www.rane.com/par-d.html#decibel Rane Professional Audio Reference entry for "decibel"] *[http://hyperphysics.phy-astr.gsu.edu/hbase/sound/db.html#c1 Hyperphysics description of decibels] === Converters === *[http://www.analog.com/Analog_Root/static/techSupport/designTools/interactiveTools/dbconvert/dbconvert.html Vpeak, VRMS, Power, dBm, dBu, dBV converter] *[http://www.sengpielaudio.com/calculator-db-volt.htm Conversion: dBu to volts, dBV to volts, and volts to dBu, and dBV] *[http://www.sengpielaudio.com/calculator-soundlevel.htm Conversion of sound level units: dBSPL or dBA to sound pressure p and sound intensity J] *[http://www.sengpielaudio.com/calculator-volt.htm Conversion: Voltage V to dB, dBu, dBV, and dBm] *[http://www.moonblinkwifi.com/dbm_to_watt_conversion.cfm Strange dBm to mW conversion] ==Reference== *Martin, W. H., "DeciBel – The New Name for the Transmission Unit", ''Bell System Technical Journal'', January 1929. Units of measure Sound Acoustics
Decibel
== Bel vs. Decibel, which came first? == The part until the next line has been moved over from Talk:Decibel: Earlier I thought Alexander Graham Bell coined the term "bel" as a measurement of sound and that it was later determined to be so coarse that 1/10th of it proved more useful (the decibel). On seeing someone on this page claim that Bell coined the phrase "decibel" I looked up its history in the Oxford English Dictionary. The OED has their earliest recorded uses in 1928 and 1929; Bell died in 1922. *the earliest few quotations the OED has on file for "decibel": ''"1928 Electrical Communication VII. I. 33/2 If common logarithms are used, the reproduction is obtained in Decibels. 1929 W. H. MARTIN in Bell System Techn. Jrnl. VIII. 2 The Bell System has adopted the name ?decibel? for the ?transmission unit?, based on a power ratio of 10·1... For convenience, the symbol ?db? will be employed to indicate the name ?decibel?. 1930 Discovery Dec. 398/2 The band-pass filter, which follows the low frequency modulator, allows the lower side-band to pass with an attenuation of six decibels."'' *the earliest few quotations the OED has on file for "bel": ''"1929 W. H. MARTIN in Bell System Techn. Jrnl. VIII. 2 It was further suggested that the naperian unit be called the ?neper? and that the fundamental decimal unit be called the ?bel?, these names being derived from..Napier..and Alexander Graham Bell. 1930 Gloss. Terms Electr. Engin. (B.S.I.) 13 The bel is a unit used in the comparison of the magnitudes of power, voltages or currents at two different points in a network of lines or apparatus."'' Clearly the term "bel" was in use before the term for 1/10th of it came about. Yet it seems odd to me that the terms did not see print for almost a decade. Anyone? Specifically, I'd like to know who made the suggestion for the terms "napier" and "bel." I suspect it wasn't Alexander Graham Bell. --user:Koyaanis Qatsi I've generalised the article a bit, since decibels are not just used for acoustics (e.g. they're used to measure the gain of amplifiers and loss of transmission lines.) -- DrBob == Acoustic decibel reference == How likely is it, if I find a claim that a sound is at, say, 120dB, that the reference level is indeed 20 micropascals? Similarly, if author A claims that one sound is so many dB, and author B claims that one sound is so many dB, how safe is it to compare the measures given, if neither indicates the reference level? --User:Ryguasu 04:38 Feb 26, 2003 (UTC) == Watts vs watts per square meter == This 0 (zero), decibel level also corresponds to one billionth of a watt, 0.000 000 000 001 watt, roughly a mosquito flying 10 feet away. :Watt would be total power, not related to distance; also http://ccms.ntu.edu.tw/~karchung/decibels/decibels1.ppt says 40 dB. - User:Patrick 09:52 Apr 16, 2003 (UTC) == List of acoustic decibel levels == It'd be nice to have a list of example decibel levels on this article - User:Khendon == Decibel vs Bel, separate article for acoustics or not == # Do acoustic decibels and general decibels really need to be separate articles? # Since decibel is much more commonly used than bel, shouldn't it be the title of the article? kind of like kilogram being the standard SI unit, even though it is a basic unit with a prefix. - User:Omegatron 00:47, Apr 17, 2004 (UTC) :Agreed Omegatron, I think this article should move to decibel - anyone disagree? -- User:Rissa of the saiya-jin 00:45, 6 Jun 2004 (UTC) ::I am moving it back to decibel. It is much more common. it sounds like the richter scale uses bels without calling it as such, but EVERYTHING else uses decibels. - User:Omegatron 14:12, Jun 27, 2004 (UTC) == 20 micropascals or 2 pascals??? == This seems to say that dB SPL is referenced to both 20 micropascals and 2 pascals. I'm sure the standard (used for dBA, etc.) is only one of those. Which is it? - User:Omegatron 17:43, Nov 23, 2004 (UTC) :20 micro. someone put in 2 N/m^2 without any exponent for some reason. fixed now. - User:Omegatron 17:51, Nov 23, 2004 (UTC) == which dB? == Please make sure the reference for all values listed as only dB are clear from context. (dB SPL, dBu, etc.) - User:Omegatron 17:43, Nov 23, 2004 (UTC) == Theatre? == One of the values in the table is "Theatre". That's too vague to be at all useful (to me, at least). An empty theatre? A filled theatre of whispering people? Sitting 5m away from Hamlet giving his soliloquy? A theatre showing a Jerry Bruckheimer movie? (From context, probably not the last one, but that's still a decent range.) ==Kerbside vs Curbside== The original spelling in this article was by Heron on 18 Nov as Kerbside. This is fine. Unless you wish to remove the entire entry, please leave the spelling in its original sense. User:Icairns 00:29, 8 Dec 2004 (UTC) :Not that it's terribly important, but the policy seems to be one of consistency for the whole page: :* Wikipedia:How_to_copyedit#Correcting_spelling :* Wikipedia:Tutorial_(Keep_in_mind)#U.S._English_vs._British_English :- User:Omegatron 15:19, Dec 8, 2004 (UTC) == dBA incorrect? == according to whom? - User:Omegatron 02:57, Dec 12, 2004 (UTC) :Exactly my question. The link is to dB(A), and that's what I've seen the manufacturers use ([http://www.electrolux.com/node507.asp]).--User:Jerryseinfeld 18:38, 23 Jan 2005 (UTC) ::Well yeah, manufacturers use it all the time (not just "historical sources"). Someone is claiming that it's not official, though, because it implies a reference to an "A" unit, like dBV implies a reference to a volt. Either this is a small minority opinion, or it's a new opinion that just hasn't gained a foothold yet, like binary prefixes like "mebibyte". My personal opinion is that it's fine to use it the way it is. It's just a shorthand way of saying it's A-weighted. Like saying miles (survey). In addition, the standard acoustic version is just "dB" with ''no'' qualifier (it should be dB SPL or dBSPL or dB(SPL)) which leads laymen to believe that a dB is a unit by itself. I would much rather see people using dB SPL than see them stop using dB (A). - User:Omegatron 20:08, Jan 23, 2005 (UTC) === Unit symbol dB rather than dBA, dB(A) etc === When making acoustical measurements and determining, for example, an A-weighted sound pressure level, the measured sound pressure is still compared with the reference sound pressure (20 μPa), and the unit symbol should still be dB. This is standard usage in definitions given in modern ISO and IEC standards, and is now mandated for ANSI standards developed by the Acoustical Society of America in their ASACOS rules. The preferred form of expression is "the A-weighted sound level was xx dB" or ''L''A = xx dB. There are many historical sources which use "dBA", or "dB(A)" or talk about "dBA levels", and these should be understood as indicating A-weighted sound levels, although the unit symbol is incorrect. Unit symbols such as dBu or dBm indicate the reference value used to determine the level, and thus are correct. But the A denotes a frequency weighting, not a reference quantity. == Potential inclusion in SI == Any citation to support the claim that "(BIPM) has recommended its inclusion in the SI system."? *This doesn't even seem plausible to me—it's outside BIPM's bailiwick. More likely the Comité International des Poids et Mesures (CIPM), or the Consultative Committee on Units which is, I think, under the CIPM and advises the CGPM Also, does that recommendation include the neper as well as the decibel? User:Gene Nygaard 01:51, 19 Jan 2005 (UTC) == RMS == "dB(0.775 V)—(usually RMS) voltage amplitude" :Is it ''ever'' not RMS? Every site I see says it is referenced to RMS. - User:Omegatron 02:50, Jan 19, 2005 (UTC) == Is this website violating the GNU License?? == http://encyclopedia.laborlawtalk.com/Decibel if so, i find it funny that a "law" site is guilty of copyright violation. : No, it does not appear so. User:203.26.206.129 07:09, 13 Apr 2005 (UTC) : Read the bottom of the page: "This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Decibel"." User:RoceKiller 10:16, 14 Apr 2005 (UTC) == dB Doubling Versus "Perceived" Doubling == So I always thought that 10dB represented a doubling of the sound intensity but now I find out that this may be technically incorrect. That 3dB represents a true doubling of sound pressure and that 10dB is where the human ear ''perceives'' the pressure as doubling. Can anyone confirm this? It would be nice for the article to clarify this. :I'm not sure of the actual answer, but these are where you should look. I'm going to try to figure it out, too: 3.01 dB corresponds to a doubling of sound power, not sound pressure. How we perceive it depends on amplitude and frequency, and would be derived from the equal-loudness contour. Also see the units of perceived loudness, phon and sone. - User:Omegatron 16:36, Apr 29, 2005 (UTC) :Wow. You helped me realize there are a lot of confusing, overlapping sound measurement articles. I've created a template to keep them tied together: Template:Sound measurements - User:Omegatron 16:49, Apr 29, 2005 (UTC) == Amplitude vs power == I'm still sketchy on the relationship between power and amplitude and dB. You can't convert from a power to a dB to a voltage, for instance, unless you know a load resistance. I'm especially confused because you can't convert amplitude --> dBFS --> power in digital land which doesn't even have load resistance. What does "power" even mean for digital?? - User:Omegatron 20:13, Apr 29, 2005 (UTC) YEEARG - and I had explicitly edited this article to correct this, and it has been reverted. decibels are DEFINED AS 10log10(x) - PERIOD. This 20log10 crap is WRONG! dB are NEVER 20log10 of ANYTHING. Now, when you are talking about dBWatts (or any derived units like dBmW) you can compute the CHANGE in level by computing 20log10(V1/V2), but that is a simplification of the full formula 10log10( (V1*V1/R)/(V2*V2/R) ). But it is also perfectly valid to speak of dBV - and a 10 dB increase of a 0dBv signal yeilds 10 volts, NOT 100! dB absent any unit is a RELATIVE measurement - I can speak of a 6dB increase of my bank account (a thing much to be desired), but I cannot speak of having 6dB in my bank account - I can say I have 36dB$ in the bank, but I *have* to supply a unit for an absolute measure to be meaningful. I design test equipment for a living, and this confusion causes us NO END of problems. People will increase the deivation of an FM signal by 2, and expect to see the audio spectrum analyzer increase by 6 dB. The spec-an is measuring deviation, so a x2 increase is 10log10(2) = 3dB. To get a 6dB increase we would have to be reporting (kHz deviation)^2 - now what physical property does that describe? Please - dB is 10log10(x) ALWAYS - not 20log10! Revert the reversion of my changes, please! N0YKG 10 May 2005 : Here's your chance to be bold and put the above explanation why 20 log 10(X/Xref) is wrong into the article. Though I admit I don't see why it's wrong to say 20 log ((V1/V2)) as opposed to 10 log((V1/V2)^2), assuming the circuit impedance is the same. dB should always be used to refer to ratios of power quantities, not to ratios of amplitude quantities...but we often cheat and say 20 log (amplitude/reference amplitude) --User:Wtshymanski 19:02, 10 May 2005 (UTC) :On the one hand, you say dB should only be used for power quantities, but then you say that dB could be used for your bank account. Also: :* 0 VRMS = 0 dBV :* 10 VRMS = 20 dBV :* 100 VRMS = 40 dBV :According to [http://www.analog.com/Analog_Root/static/techSupport/designTools/interactiveTools/dbconvert/dbconvert.html this], which claims to be based on the ANSI T1.523-2001 definitions, which I would download, except [https://www.atis.org/atis/docstore/doc_display.asp?ID=928 it costs $175] - User:Omegatron 20:21, May 10, 2005 (UTC)
See other meanings of words starting from letter:
D
DA | DB | DC | DE | DF | DG | DH | DI | DJ | DK | DL | DM | DN | DO | DP | DR | DS | DT | DU | DW | DX | DY | DZ |Words begining with Decibel:
Decibel
Decibel
Decibels
Decibel_(Acoustics)
Decibel_(acoustics)
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