Why we use decibels

How fast? How far will light travel in the blink of an eye? How long does it take for RF signals to travel through 1 foot of hardline feeder coax? Eighty-seven percent of , It takes a mere 0. A nanosecond is a billionth of a second! The answer is about 5. A really long distance. At that speed, it will take 16, years to travel one light year.

If the Voyagers were headed directly to the nearest star beyond our solar system — Proxima Centauri, just 4. Where is warp drive when we need it? The cable industry has been using singlemode optical fiber in HFC network architectures since the late s. A common optical wavelength for transporting signals from headend to node is 1, nanometers nm. Show 3 more comments. I respond with a quote from the book Recording Studio Design : Our hearing perception tends to correspond to changes in sound pressure level, and it was stated earlier that a roughly 10 dB increase or decrease was needed in order to double or halve loudness.

The emphasis in both quotes is mine. From the now removed comment thread to this answer: You are still wrong along with the non-scientific source you are quoting. Alfred Centauri Alfred Centauri Add a comment. For example AlfredCentauri quotes incorrect statements from "the book of Recording Studio Design" without critically analyzing them to see that they have little to do with science or reality: it is necessary to increase the power from a source by 10 times in order to double the loudness As other have pointed out thanks!

This phenomenon is known in psychophysics as the Fechner law that applies to all human senses: Fechner's law states that the subjective sensation is proportional to the logarithm of the stimulus intensity. The logarithmic scale has been well explained on this forum earlier by dmckee and others: Why is the decibel scale logarithmic? Community Bot 1. That you need to increase power by a factor of 10 to double the loudness does not imply a linear dependence, since it also implies that you need to increase power by a factor of to increase loudness by a factor of 4, which is certainly not a linear relationship between power and loudness.

The very Wikipedia article on Fechner's law you link to states rather clearly that it is a poor approximation for human sound perception, so your claim that it "applies to all human senses" is undermined by your own reference. This is patently ridiculous.

You misinterpret the logarithmic law. And 60 decibels to decibels increases the loudness by 8 units. Thus, according to a logarithmic scale, decibels would be a little more than twice as loud as 60 decibels. Please explain the mistake in my reasoning.

Show 8 more comments. Featured on Meta. Now live: A fully responsive profile. Linked Related 2. Hot Network Questions. Measurements made on this scale are expressed as dBA. The C scale varies little over several octaves and is thus suitable for subjective measurements only for moderate to high sound levels. Measurements made on this scale are expressed as dB C. There is also a rarely used B weighting scale, intermediate between A and C.

The figure below shows the response of the A filter left and C filter, with gains in dB given with respect to 1 kHz. For an introduction to filters, see RC filters, integrators and differentiators. ISO Loudness, phons and sones, hearing response curves The phon is a unit that is related to dB by the psychophysically measured frequency response of the ear. At 1 kHz, readings in phons and dB are, by definition, the same.

For all other frequencies, the phon scale is determined by the results of experiments in which volunteers were asked to adjust the loudness of a signal at a given frequency until they judged its loudness to equal that of a 1 kHz signal. To convert from dB to phons, you need a graph of such results. Such a graph depends on sound level: it becomes flatter at high sound levels. Recording level and decibels Meters measuring recording or output level on audio electronic gear mixing consoles etc are almost always recording the AC rms voltage see links to find out about AC and rms.

So what is the reference voltage? Intensity, radiation and dB How does sound level or radio signal level, etc depend on distance from the source? So, if we double the distance, we reduce the sound pressure by a factor of 2 and the intensity by a factor of 4: in other words, we reduce the sound level by 6 dB.

If we increase r by a factor of 10, we decrease the level by 20 dB, etc. For fresh water, the specific acoustic impedance for water is 1. So a sound wave in water with the same pressure has a much lower intensity than one in air. For many cases in communication, isotropic radiation is wasteful: why emit a substantial fraction of power upwards if the receiver is, like you, relatively close to ground level.

For sound of short wavelength including most of the important range for speech , a megaphone can help make your voice more anisotropic. For radio, a wide range of designs allows antennae to be highly anisotropic for both transmission and reception. Example problems A few people have written asking for examples in using dB in calculations.

All else equal, how much louder is loudspeaker driven in its linear range by a W amplifier than by a 10 W amplifier? I am standing at a distance R from a small source of sound size much less than R , at ground level out in the open where reflections may be neglected.

The sound level is L. If I now move to a distance nR n a number, and nR still much greater than the size of the source , what will be the new sound level? If, in ideal quiet conditions, a young person can hear a 1 kHz tone at 0 dB emitted by a loudspeaker perhaps a softspeaker? An amplifier has an input of 10 mV and and output of 2 V. What is its voltage gain in dB?

What is the difference, in dB, between the irradiance light intensity on earth 8. Occupational health and safety Different countries and provinces obviously have different laws concerning noise exposure at work, which are enforced with differing enthusiasm.

Some FAQs How loud is an aircraft? A train? A person singing? A dog barking? A power tool? The answers to this question vary considerably. It depends strongly upon how far away you are, whether you are indoors or not, whether there is reverberation, how strong the particular source is and what its spectrum is. To give values, without being very specific about the conditions, would be somewhat misleading.

Because the rest of this page is intended to be reliable, as far as it goes, I'd rather not give values here. How does one "add decibels"?

If the sources are coherent which usually means that they ultimately come from the same source , then there may be complicated interference effects. In most cases, where the sources are independent, one can add the intensities and then convert to decibels. However, if you are given the sound levels in dB A , it is not so easy to go back to intensity, and one must know something about the spectrum of the sound. If you know the distribution of the sound in different frequency bands, you can use the applet on this link.

Some of the questions on our FAQ in music acoustics relate to decibels, including Why do the sounds of two musical instruments always reinforce, and never cancel out? How much does one more violin add to the sound level of a section of n violins? Does adding two equal sounds give an increase of 3 or 6 dB? What is the loudest sound? Is there really no sound in space? How loud is the fusion of two black holes? A colleague and I wrote a little paper about this for Nature Physics. The Telegraph?

Both the British Royal Navy and the Emperor of Russia were involved in the earliest, practicable designs. And so on. Engineers immediately saw that early phone calls lost signal strength over distance: signals grew fainter the further they had to travel. To fix the situation, engineers needed a method of quantifying this loss in the first place. They needed a measurement, one to define the amount of signal lost over, say, a mile of standard cable.

Capitalism being capitalism, a number of measurements were put forth by competitive entities. There was no standardization—companies and countries had their own systems of measurement, making comparisons exceedingly complicated.

They also voted to change the name. Capitalism strikes again! It was decided that the decibel a smaller unit would be used instead. A decibel is a unit that expresses the ratio between one value and a second previously-determined value—where the value in question is electrical, acoustical, or digitally-sonic in nature, and the scale of the measurement is logarithmic.

The intensity of a sound in decibels can be expressed as the following formula, in which S1 and S2 are the intensity of the sound and a reference intensity respectively:. On a logarithmic scale, values change quite differently.

This is the first reason the decibel is so useful to us: we can quickly calculate, automate, move, or jump through values that are exceedingly wide in range, in a manner that is easier to digest. The log scale correlates better to how we perceive changes in SPL sound pressure level in the real world. However, a linear scale sees these values spaced evenly, while a logarithmic scale has finer resolution as you move up the scale. This is extremely helpful from a practical standpoint, in something like a level fader.

We use decibels to express and simplify relationships between voltage, current, resistance, and other variables, depending on the measurement in question. In an analog system, a signal can get stronger than, and even pass the point of distortion. Digital systems differ in that there is a set ceiling, above which nothing can happen.

What does this actually mean, in terms of sound? In a bit system, any recording with a value higher than 0 dBFS will be registered as a neatly clipped square wave for the duration.