AUDIOBOOK PRODUCTION TECHNIQUE ARTICLE
In my role as an audiobook producer/editor/mastering engineer I continue to find it baffling that so many editors fail to understand the vital role they play in protecting the hearing of audiobook listeners. Unlike much modern music, audiobooks rarely get put through a final limiting phase, which means that if you've left any sudden 'explosively' loud peaks in your edit, these will be experienced by the listener.
So, why is this something worth talking about? Well, consider for a minute that the majority of audiobook consumers listen using in-ear headphones, often whilst commuting, and also with the volume turned up, so they can enjoy the mellifluous vocal tones of your wonderful narrator. There's no 'air-gap' protection between the headphone driver and their ear-drum as with speakers or over-the-head headphones. The sound is direct...and if it suddenly 'explodes' in volume, you risk damaging their hearing...possibly permanently.
Here's an example of what I am talking about...this is a edited file I was sent to master ready for distribution:
There are a couple of things to note here:
 The overall volume of the audio is too low...the editor should have raised the gain at least 3-4 dB BEFORE editing to ensure they could hear all the background noises, etc...
 There's a great big EXPLOSION of sound in the middle which is approx. 10dB louder than the audio surrounding it.
Now, as an editor, we have to bear in mind the context of this sudden loudness. In most instances the narrator is reading a character line where there is shouting, or expletives, or some other justifiable reason for the amplitude. Of course, a well set-up studio would have factored such increases in and used a soft but capable compressor across the vocals to [a] raise the overall gain and [b] control the sudden gain changes. In this instance the studio wasn't correctly setup, and so the editor has to deal with the issue. At least, in this case, there isn't any distortion caused as the maximum gain tops out at just under 0dB.
Let's look at how the editor SHOULD have dealt with such an issue. First, a close-up of another area of contention later in the same file:
Here we can see the surrounding audio is averaging peaks of -12dB but there is a sudden explosive gain jump to -2dB...a 10dB jump! They have left this for the mastering engineer (me) to deal with. I could just process the whole file through a compressor and end up with a file that looks fine, but sounds as though someone has aggressively bundled the peak audio in a hessian sack and thrown it in a river!
Instead I use gain reduction, and my ears, to reduce the overall gain of the section to something more in line with the surrounding audio WITHOUT drastically altering the impact of the narrative:
Notice there is still a 5dB change in gain, so the listener will still hear the impact of the narrator's choice to 'go loud', but it is a less aggressive gain jump, and protects their eardrums from the potential damage such a sudden and dramatic increase in volume could cause.
Now I do the usual mastering processes, of bringing up the overall file volume using soft-knee compression and very careful limiting, and using some soft EQing to balance out the narrator's tone and the imperfection of the studio recording, and we end up with this:
Now the overall average volume is around -7dB, with lows around -15dB with peaks at -3dB max (the client's spec...and good practice). We have dynamic range, but a stronger overall gain which means the listener doesn't need to turn up the volume of their device too much, and the 'explosive' section is in line with the audio around it whilst retaining its narrative impact.
So, if you are editing audiobooks, do keep in mind that we are the gatekeepers of best-practise audio and the protectors of our listeners' eardrums. Just about all linear-editing software packages will allow you to highlight a section and reduce the gain...and if your DAW doesn't, then consider moving to one that does. DON'T rely on a mastering engineer to smooth over these issues as you may not have access to one...YOU may be the final stage before delivery. Consider your overall volume and try to stick to a rough rule of thumb that sudden gain increases should not be more than 5-6dB. Double check the client spec for peak values, and use your eyes as much as your ears...if it looks spikey and dangerous, it most probably is.
ABOUT THE AUTHOR
Neil Gardner is the managing director of leading UK audiobook production house Ladbroke Audio, and audiobook publisher Spokenworld Audio. He has 30 years experience in radio and audio, is an international award-winning producer/director/writer and loves nothing more than making audio for all ages.