![]() Theoretically, the absolute and relative scales cannot be readily interchanged. For completeness, I'll start by explaining the relative scale anyhow. ![]() In my volume controls article, the focus was mostly on the relative scale because that is what volume controls are about, but in this article it's the other way round. It allows us to cope with an enormous dynamic range, from a silent whisper to a roaring jet engine and anything in between. Our ears also have an approximately logarithmic response to sound. We do not perceive sound in a linear way. Why is it practical to use the decibel to measure the loudness or amplitude of sound? Because it matches well with how human hearing perceives sound loudness. Professional audio equipment will have volume controls displaying dB values. The decibel is used to measure sound signal levels, both in an absolute way to denote how “loud” is a sound carried by pressure waves, as well as in a relative way to denote what is the amplitude or power of an electrical signal representing sound inside a machine. This is always the case, not just when it seems most convenient, and this is also where a lot of the reasoning about decibels takes a wrong turn because people keep thinking linearly while they should be thinking logarithmically. What this means in practice, is that each time the value being measured is multiplied by the same factor F, the same offset is added to the logarithm of the measurement: log( x Left: exponential curve right: logarithmic curve. When for some reason you can only compute the natural logarithm ln( x), basic maths teaches us that log( x) = ln( x)/ln(10). In this text, “log( x)” denotes the 10-base logarithm of x. The slope of the curve decreases with increasing x: ever larger input increments are needed to keep raising the function's response by the same step size. ![]() A logarithmic function turns multiplications into sums. The logarithm is the inverse function of the exponential function: if x = 10 y, then y = log( x). It is very important to note that the unit is logarithmic. In practice the bel proved to be too large for general use, therefore it is almost always used with a factor 1/10, yielding the decibel, denoted with the symbol dB. The bel is the 10-base logarithm of the ratio of two power values. ![]() What is important is that it is a relative unit, that compares one measurement either against another or against a reference value. The ‘bel’ is a unit of measurement named after Graham Bell, used to compare signal or power levels of any kind, and is denoted with the symbol B. The errors stem from incomplete understanding of logarithms, and/or the properties of the human auditory system. Singing loud is already 70 db plus which is 10 to the ten which is ten TRILLION times kinetic energy being produced.Īll those claims are wrong in some way, some more than others, some have multiple mistakes combined. 60 is normal household conversation level.So 115 to 129 (14db higher) is roughly 5 times louder than the original car horn. ![]()
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