decibels – dB, dBFS and so on
If you’re getting involved in audiobooks, you’re going to hear a lot about decibels – usually abbreviated as dB.
What is a decibel?
The decibel originated in the early 20th century as a measure of power loss along a distance of standard telephone cable. I won’t go into the details here (Wikipedia has it in exhaustive detail if you’re interested)* but the key things to note are:
- it’s a measure of power – i,e, volume, loudness
- its a relative measurement, not an absolute one
Let’s unpack these.
The decibel scale is logarithmic; a ten-fold increase in power corresponds to a 10dB increase. Logarithmic scaling fits well with the way the human ear perceives changes in volume. That 10dB increase will “sound” to a human ear like a doubling of volume.
However, a doubling of actual “power” – i.e. what’s being pushed into your amplifier – corresponds to a 3dB increase. This is a far less noticeable volume change to the human ear. Just to really confuse you, a doubling of signal amplitude (i.e. voltage, sound pressure) corresponds to a 6dB increase. This will end up mattering to you if you work with a stereo track with panning, amongst other things.
Measurements like mass (e.g. kilograms), length (e.g. metres) or volume (e.g. litres) are absolute. They just “are”. But decibels measure the difference between one thing and another, so to use dB as an absolute we need to add “compared with…” . This is often done by appending a further abbreviation. For example:
- dBV
- dBu
- dB (A)
- dBFS
In the digital world, you will often see “dBFS” – which literally means “decibels compared with full-scale”. To find out what “full-scale” means in this context, head to this article.
An audiobook example of dBFS is Audible’s technical standard for peak levels, which must not exceed -3.0 dBFS.
One more thing
In the digital world, “full scale”, the maximum level allowed, is referred to as zero. So, every dBFS value you ever see will be a negative number. “-3.0 dBFS” as mentioned above means 3dB below full-scale. This is discussed in the article about full-scale.
Why you need to care
When you’re dealing with audiobook production you’re going to see dB’s mentioned all over the place. All the technical requirements that you must meet to have an audiobook accepted by acx, Audible, etc. are expressed in decibels.
You don’t need to understand the history behind the decibel or the mathematics behind what it measures. You just need to be comfortable with using dB’s to measure what you’re doing. Whatever DAW you use to record your audiobook, it will be talking to you in dB.
on to digital full-scale and headroom>>
*I do try to resist my natural tendency to get over-technical and indulge my love of facts and figures. If there’s something you think I should go into more deeply, drop me a line or write a comment.
Justin Hill has been in the recording business for more years than he likes to talk about but has traded as The Other operation since 2013. In early 2020, just as the COVID lockdowns started, he decided to build a dedicated spoken word studio.
Despite materials and equipment suppliers either being closed or having no stock, and delivery drivers being unwilling to come to the door, Landen Park Studio actually got finished and had its first session in August 2020.
Since then, Landen Park Studio has recorded countless audiobooks and hosted countless voiceover sessions with Justin Hill at the helm. Many of these audiobooks have been self-narrated by authors who’ve never recorded an audiobook before.