Understanding Decibels

When dealing with musical instruments, gear, mixers, software, and other items like amplifiers, you will often see the term “decibel” or often abbreviated as “dB”

The decibel is the unit we use to describe the level relationship between two signals. It is really important to understand that the term decibel, by itself, only refers to a comparison of levels.

A decibel is dimensionless, unless a reference is given, as we will see below.

A characteristic you must never forget about the decibel is that it is logarithmic function and not a linear one.

Guitar players might be familiar with the terms “log taper” vs “linear taper” when it comes to volume and tone knobs on a guitar.

Difference between logarithmic response vs linear response in common guitar potentiometers

Let’s look at some common relationships, to get a better understanding of the decibel

If you double the power (expressed in watts) of an amplifier, you gain 3dB. In a second you’ll see why going from a 50 watt Marshall, to a 100 watt Marshall isn’t nearly the volume jump you’d expect.

If you double the amplitude of a signal (for this case, expressed as peak to peakvoltage), you gain 6dB

Now, if you want to get twice as LOUD as another signal, THAT takes 10dB’s! So if you want an amp that’s twice as loud as your 50 watt Marshall, you are going to need a FIVE HUNDRED watt head!

REMEMBER: Any time you see “dB” without another letter after it, you are seeing a relationship between levels, and not an absolute statement about the level of a single, lone sound