In this video, you'll learn everything you probably need to know about decibels.
But if you're new here, welcome. My name is Kyle. If you want to learn audio
production online, subscribe to Audio University. The decibel is one of the
most confusing concepts in audio production. Trying to wrap your mind
around every detail all at once might leave you feeling overwhelmed. The truth
is: for most people, learning a few key principles about the decibel will be
sufficient for working in the audio industry. the first thing you should know
is that decibels can represent large ratios using simple numbers. That's one
reason the decibel is so useful for describing sound pressure. Humans are
capable of perceiving a vast range of sound pressure - from very subtle to very
extreme. Discussing sound pressure in absolute units can be challenging. The
pascal is an absolute unit of measurement that describes air pressure
in terms of force per square meter. The limits of human perception of sound
pressure range from 20 micropascals to 20 pascals - a ratio of 1 to 10 million!
It's much easier to discuss sound pressure in terms of decibels. This chart
shows a side-by-side comparison of the two. You can see sound pressure in
pascals on the left and sound pressure level in decibels on the right. Decibels
present these quantities in a way that is much easier for us to interpret. In
audio production, the decibel is also useful because it presents sound
pressure on a scale that's much more relevant to the way humans perceive
loudness. Most of us are accustomed to thinking in linear terms. For instance,
twice as many letters produce a word that's twice as long. This mode of
thinking, however, does not hold true for the way humans perceived loudness.
Thinking in linear terms, you might suspect that twice the amplifier power
produces a sound that's twice as loud. This is not the case. The way humans
perceive loudness is more similar to a logarithmic scale than a linear scale. In
a linear scale, each step is the same size. For example: 10 - 20 - 30 - 40 (where each
step is an addition of 10). In a logarithmic scale, each step has the same
proportion. 10 - 100 - 1,000 - 10,000
(where each step is multiplied by ten). As sound pressure increases, more and more
power is required to create the same perceived increase in loudness. The
decibel accounts for this fact by presenting absolute units on a scale
that better relates to human hearing. A decibel is a way of describing the ratio
between two quantities. Saying, "The drums are 120 dB", is an incomplete statement.
That's because the decibel alone has no value. It's only when you draw a
comparison to something else that the decibel has meaning. You could instead
say, "The drums are 20 dB louder than the guitar". This statement is more
meaningful because it draws a comparison between the level of the drums and the
level of the guitar. The level of the guitar in this case is the 0 dB
reference point. In the case of a fader on a mixing console, unity gain is the 0
dB reference point. Pushing the fader above 0 dB adds gain to the signal.
Pulling the fader below 0 dB attenuates, or reduces, the signal.
Decibel values above unity are represented by positive numbers and
decibel values below unity are represented by negative numbers. For many
applications in audio production, there are standardized reference points that
define 0 dB in absolute terms. Each application has its own suffix: dBm, dBu,
dB SPL, etc. Here's a helpful chart that defines the 0 dB reference point in
common audio applications. This chart brings meaning to the various types of
decibels. The formula for decibel calculations will make a lot more sense
if you first understand the relationship between decibels and Bels. This is the
formula for finding the ratio between two power quantities in Bels. "Power 1"
is the reference power and "Power 2" is the measured power.
Let's try finding the ratio in Bels between 10 watts and 100 watts. The
formula would look like this. Dividing 100 by 10 gives us the ratio between the
power quantities, which is 10. Using the log function of the calculator, we can
find that the log of 10 is 1. Therefore, the ratio between 10
watts and 100 watts is 1 Bel. Now that you've learned the formula for
calculating ratios and Bels, let's take a look at how to adjust that formula to
calculate ratios in decibels. A decibel is 1/10th of a Bel. For comparison's sake,
let's use the same power quantities we used before: 10 watts and 100 watts. This
time, finding the ratio in decibels. To start, divide 100 by 10 to find the ratio,
which is 10. Use a calculator to find the log of 10, which is 1. Multiply 1 by 10 to
convert bells to decibels. The ratio between 10 watts and 100 watts is 10
decibels, or 1 Bel. For many, the most confusing aspect of the decibel is
deciding which formula to use in a given situation. The formula for decibels is:
10 * log(Power2/Power1). In some situations, however, you might see
this formula: 20 * log(Value2/Value1). Why are different
formulas used and how do you choose which formula is appropriate in a given
situation? The decibel is a power related ratio.
When finding the ratio between two quantities of acoustical power or
electrical power, use the basic formula we learned in the last section. The
decibel can be used to represent the ratio between non-power quantities, such
as sound pressure and voltage. When calculating voltage and sound pressure
levels, use this formula. The reason we multiply by 20 is explained by the power
equation. In this equation, W is power, E is voltage, and R is resistance. Notice
that voltage is squared in this equation. Power is proportional to voltage squared.
Quantities that are not power must be made proportional to power. Another way
to come to the same answer would be to use this formula, squaring each voltage
value before finding the ratio. Anytime you're comparing power quantities in
decibels, multiply the Bel formula by 10. Anytime you're comparing
non-power quantities in decibels multiply the Bel formula by 20. It's
hard to get a straight answer when asking someone, "How many decibels is a
doubling?". Well, that's because it depends on what's being doubled. As you just
learned, non-power quantities must be made proportional to power in order to
be represented in decibels. Following that logic, the decibel value used to
describe a doubling of a power quantity is different from the decibel value used
to describe a doubling of a non-power quantity. It's helpful to remember the
decibel value for representing a 2:1 and 10:1 change in power, voltage,
and sound pressure level. Use this chart for reference. Everything discussed in
this video can be found in the post I wrote on AudioUniversityOnline.com.
I'll put a link to that post in the description of this video. If you got
value out of this video, hit the "Like" button, share the video, and subscribe to
Audio University. Thanks for watching!