An Introduction To Decibels

What You Always Wanted To Know About Decibels

Many times in previous articles we’ve mentioned the word “decibel”. Of course, the world of sound and audio basically revolves around decibels. But what in reality does the concept of decibel entail? Here is our view on the decibels and how internalizing the concept can be useful if you either work as a sound designer, sound mixer, or even within the audiovisual industry. So, first things first: when it comes to trying to define decibels, there’s no better way than to put it this way: decibels are odd units, and there are at least three main reasons for such definition:

Decibels Are A Logarithmic Unit

When it comes to unveiling the intricacies of the definition of decibels, we first need to mention one of its aspects: a decibel is a logarithmic unit. Of course, our mind is not traditionally fond of logarithmic units, mostly due to the fact that we’ve become accustomed to deal with other types of units such as distances or weights, which are also present in our lives every day. Nonetheless, the concept of logarithmic units is highly useful, especially when we want to represent a sheer array of different figures or values.

If we were to take a value and make it 3, 4 or even 5 times bigger, we would see that the resulting figure would get incredibly huge on a logarithmic scale unlike on the traditional linear scale. Why? The reason behind this evident difference is that, while linear scales are based on multiplication, a logarithmic scale is based on exponentiation. Thus, if we were to increase the number 10 5 times, we would get to the value of 100,000. That indeed is really convenient whenever we want to get the full picture of a set of data ranging from dozens to even millions.

Some other units simply work fine on the regular linear scale, as we normally move within a rather small range of figures. That’s why it’s easy for us to measure the distance between cities; but what if we wanted to measure the distance between cities throughout the galaxy? (Of course, assuming we’re such an advanced civilization, that we managed to find life in other planets.) If we were to use a linear scale to represent the difference in distance between Los Angeles and Orion, the difference would be 1200000000000000 km, which is undeniably a really tough figure to look at; however, on a logarithmic scale, the difference would be just 16.8 log km.

The logarithmic scale offers a solution for this issue since it seamlessly provides an easy-to-understand figure while covering several order of magnitude. Like the cities used above as an example, some other natural phenomena can be expressed on a logarithmic scale, since they span through several orders of magnitude as well. Think of earthquakes, pH and, of course, sound and loudness. By using a logarithmic scale to measure and express some events, we can get a more accurate version of the models of nature.

Decibels Are A Comparative Unit

Once stated that decibels are a logarithmic unit, we have now a way to simply scale and measure different events, ranging from a simple whisper to a rocket take-off. Nevertheless, it’s not that simple. Every time we say something is 70dB, we are not making, in reality, a direct measurement —in fact, we are comparing two different values.

Decibels are the ratio between a specific measured value and a reference value. Simply put: decibels are a comparative unit. Stating that something is 30dB is as incomplete as saying that something is 30%. Thus, we need to specify the reference value we’re using, or, in other words, 20dB respect to what? What kind of reference value can we use then? And that’s what brings us to the third and last dimension.

Decibels Are A Versatile Unit

Given the fact that the vast majority of people associate decibels with sound, it’s clear that they cannot associate its measurement ratio with the value of any other physical property. These properties can be also associated with audio, like pressure or voltage, or may have little or even nothing to do with audio, like reflectivity. Decibels are found across all industries, not only audio. Take, for example, video, optics or electronics. So, after laying out all this information, what’s a decibel? A decibel is a logarithmically express ration between a pair of physical values.

Screaming In Outer Space

No matter how much Star Wars tries to convince us of the possibility of actually conveying sound’s energy in outer space, reality dictates otherwise. Sound’s energy requires a physical medium to go and travel through. When sound waves disturb such mediums, there are actual measurable pressure alterations as the atoms end up moving back and forth —the louder the sound, the more intense the alteration is.

In Summary

A decibel is based on the logarithmic scale which, of course, works very well when displaying a large range of values. It is also a comparative unit that always uses the ratio between the measured value and the value used as a reference. Additionally, decibels can be used with any physical property aside from sound pressure. They also use reference values so the numbers being managed are more significant.

*The images used on this post are taken from Pexels.com