Having a whisper quiet noise floor is critical for all audiobook projects. But what is noise floor? And what do you do if your audiobook project gets rejected by distributors because it is too noisy?
In order to better understand this problem and how to fix and prevent it, you need to first understand what noise floor even is. The following is some general knowledge on noise floor, and some tips on how to meter, reduce, and prevent signal noise.
Definition – Noise floor is “a measure of the summation of all the noise sources and unwanted signals generated within the entire data acquisition and signal processing system”1. What this means related to recording audiobooks is how loud the noise on your signal is when no one is in the booth recording. How quiet is your “silence”? There is always going to be some noise there, even if it’s inaudible to the human ear. Like the definition says, it is the “summation” of all of the super low level noise that is in the signal chain introduced by microphones, preamps, cables, patches, and computer DAWs. All of this noise adds up. It is faint, mostly inaudible, but it is there, always present on any recording that you do.
Because ACX.com is widely used for publishing audiobooks on Audible.com, it’s important the know and understand their specs when it comes to noise floor. Not following this spec will lead to your audiobook being rejected by ACX.com.
How you do measure your noise floor? Use a quality meter plugin like the Dorrough Stereo Meter. Set up your DAW like you are ready to record (make sure your pre-amp is turned up to recording level!). Close the door to your recording booth, and see what the meter says. If you have a reading of over -60dB RMS on the meter, then you have a problem before you even get started.
How do you reduce noise floor? It really depends on how much you will have to reduce. The simplest way is to use a noise reduction plugin in your DAW. We use the Izotope RX noise reduction plugins for any noise issue that we encounter. You will have to be cautious with noise reduction software as it will affect the overall quality of the audio if used too aggressively.
How do you prevent a loud noise floor? If you have a bigger issue with your noise floor, then you will have to locate where the extra noise is coming from in order to really correct the problem. You can only throw so much denoising at an audio file before it starts to sound bad. If you know that your recording booth is dead silent, then you will have to inspect your whole signal chain to find out what is introducing noise to the system. Maybe it’s your pre amp, microphone, a bad cable, or a patchbay, or noise being introduced by your computer?
-60db RMS is a very reasonable minimum for noise floor for digital recording. If you are not able to achieve this, then there is either an issue with your room acoustics, or there is something making noise in your signal chain.
Simplify Your Signal Flow. For audiobooks I try to keep the most simplistic signal chain in order to avoid unwanted noise. My signal chain looks like this: Microphone > PreAmp > DAW input. Once you start introducing things to the signal chain (patch points, cabling, patchbays, computers) you start introducing more noise. Keep it simple and keep the noise out.
Still have questions? Feel free to email us at firstname.lastname@example.org or call our studio at 781-541-1535.