Noise Floor – What is the Noise Floor in Mixing

The noise floor is a term which gets mentioned in mixing terms often but without a lot of context around it. Let’s identify what the noise floor is as it relates to mixing and how we can ensure that it doesn’t become a problem in our audio.

What is the Noise Floor

noise floor

The noise floor in mixing is essentially the combined sum of all unwanted sound on a track or in our entire mix. This manifests in a number of different forms.

A few examples of the noise floor would be:

  • Electrical hardware-based sound from recording DI.
  • Ambient room sound like an air conditioner, computer fan, or low frequency sounds from outside penetrating the walls of where you’re recording.
  • Low level electrical noise generated from a microphone itself.
  • White noise related quantization errors as a result of recording or playing back at a low bit depth (more on this in a moment).

Ideally we want to have as great of a difference between the noise floor at the bottom and the point of clipping at the top in our mix.

While the noise from the noise floor is still on our tracks, if that noise floor is lower, this keeps our tracks cleaner, particularly when there’s no audio that we actually want playing.

How to Reduce Noise Floor

To better illustrate what the noise floor is, let’s talk about some things we can do to reduce the noise floor.

Record Audio at 24 Bit

As I touched on in my overview of what is bit depth, bit depth refers to the range of values which the precise and ever changing volume of audio samples can fit into.

bit depth

The exact volume of sound from one sample to the next can exist in seemingly limitless amplitude points (see parts of a sound wave).

sound wave amplitude

The greater the range/bit depth we record at, the more likely we’ll have the exact and correct amplitude point which that audio requires from one instance to the next. Not surprisingly, this makes our recorded audio sound better.

Conversely, the lower the range/bit depth we record at, the less likely we’ll have the exact and correct amplitude point which that audio requires for one instance to the next.

This forces our recording hardware and software force the actual amplitude into a value that we have, causing quantization errors which manifest in the form of unwanted distortion which actually raises the noise floor.

To REALLY simplify this concept, let’s say we only have 10 different points to assign to a sound wave’s amplitude. The exact amplitude is a 7.7, but we’re recording at a lower bit depth which isn’t capable of capturing a 7.7. Instead, that 7.7 gets converted to an 8 in what’s known as a quantization error, producing some low level white noise in the process.

You can hear the noise floor in effect simply by dropping the bit depth via your DAW down to 8 bits – an instant and constant white noise hiss as a result of quantization errors.

To identify the exact number of values associated with each bit depth, we have to do a bit of math (sorry!).

The number of values is always 2 to whatever power the bit depth is. So 8 bit depth is 2 to the 8th power, or 2x2x2x2x2x2x2x2 which equals 256.

So 8 bit depth yields 256 amplitudes sound can fit into.

Because it’s going up at a literal exponential pace, 16 bit depth yields a much higher range of 65536 values.

24 bit depth yields 16777216 values which seems staggering until we realize that 32 bit depth yields 4.294967296 × 109 values. Wow.

While there are a handful of engineers who swear by 32 (typically the same people who swear by recording at a sample rate of 96k), recording at 24 bit depth is more than sufficient to accurately and cleanly capture your audio thus avoiding an audible noise floor.

One last word on bit depth – there’s actually a process called audio dithering in which low level white noise is intentionally added to replace the distortion from quantization errors.

Whenever you downgrade audio from one bit depth to the next (like 24 to 16 – the max bit depth the physical medium of CDs can support), be sure to use dithering to replace the unwanted distortion and achieve a cleaner sound.

Mitigating Noise When Recording

An obvious fix to lower the noise floor is to eliminate as much noise as possible during the recording process.

A few ways to do that include.

  • Turn off air conditioner, humidifier, dehumidifier, and any other appliances you can.
  • Close windows, doors, sound proof as best you can from the outside, and record when outside noise is at a low like night time.
  • Most microphones you’ll use to record are cardioid pattern, meaning they pick up what’s directly in front of them. As such, point microphones away from your computer fan or any other sources of noise whenever possible.
  • Be aware of electrical noise. To mitigate this, use shorter cables, keep cell phones away from amps or your recording hardware, and plug everything directly into the wall whenever possible.

Mitigating Noise When Mixing

There is a lot we can do to lower the noise floor in the mixing stage, as well.

These include:

  • Use high pass filters on every track in your mix. Most unwanted noise occurs below 100Hz, so this filters out a lot of outside and room noise in case you couldn’t completely remove them during the recording stage. Note that I say every track because there’s always something on the low end you don’t need which will help the low end of your mix sound better (see my low end mixing tutorial).
  • Be aware of processing which can raise the noise floor on a track and with it your entire mix. For instance, when you’re compressing audio, you’re lowering the peaks and raising the rest, essentially raising the entire audio floor if you get too aggressive as can be the case with parallel compression if you’re not careful.
  • Use noise gates on your tracks to actively filter out all unwanted noise below a certain threshold.
  • Use specialized plugins like the Izotope RX line to scoop out specific problematic sounds like electrical or background noise.
  • Some plugins have features which add low level distortion noise to better simulate their analog counterparts like is the case with the “Analog” setting on the excellent opto compressor, the CLA-2A from Waves. Turn these off to keep your mix clean.

Ultimately, when you’re recording and mixing in 24 bit depth like you should be, there’s plenty of dynamic range between the noise floor and the point of clipping and thus you’ll rarely if ever have an issue.

Still, it’s important to mitigate the effects of anything which can raise the noise floor in both the recording and mixing stages, and remember to always dither when lowering bit depth from 24 to 16 bit.

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