Managing noise reduction and minimizing the interference of extraneous sound in location recordings has always been a key role for a post-sound mixer.
It has traditionally been a fairly technical skill developed over many years. However, recently, the ability to apply noise reduction has been somewhat democratised by a rapid progression in AI-powered plugins making it more accessible for those with less technical experience than would have previously been needed.
With this in mind, I thought it would be an interesting time to look into noise reduction in a little more detail and consider how it can be utilised to clean up dialogue tracks. In a follow-up post, I'll then look at some of my favourite tools currently available for applying noise reduction.
What's the Aim?
The purpose of noise reduction is to reduce the impact of unwanted noise in location or studio recordings. This can help improve dialogue intelligibility and consistency, therefore enhancing the overall quality of a film or video production while helping to maintain audience engagement and immersion.
Noise reduction is applied through various types of plugins which all operate in slightly different ways and target different issues. These plugins are operated via a DAW (Digital Audio Workstation), video editing software or stand-alone applications.
What Noises Are We Reducing?
There are a wide range of noises that can negatively impact your recordings. However, the four main groups I consider the most frequently problematic are:
Pops, bumps and clicks
Sustained background noise
Variable background noise
Unwanted reverb
Pops, Bumps, and Clicks
Normally the first areas to address will be short bursts of noise with fast transients such as pops and clicks. These can stem from microphone impacts, technical glitches or those oh so horrible mouth clicks. These artefacts will generally show up as a sharp, vertical line in the frequency spectrum.
In most audio restoration software, there will be plugins that can de-click, mouth de-click or de-crackle. These will often do a decent job and are very simple to use while being relatively discreet. Remember to only process the specific area that needs attention, not the whole audio clip, as this can have a detrimental impact on the transients and syllables of the dialogue. For example, you might lose the attack of a 'T' sound from a word.
The alternative to this, and probably preferable, would be to use spectral editing software such as Spectral Repair in the commonly used plugin suite by Isotope called RX. This give you a visual representation of the waveform and allows you to literally erase the click or replace it with a quiet section of audio - which I still find pretty incredible!
RX Spectrogram
Sustained Background Noise
Sustained background noise includes noises that cover a wide range of the frequency spectrum over an extended period and are relatively constant such as air conditioners, hum, traffic or microphone hiss.
Supressing these sounds discreetly has historically been slightly more challenging than removing pops and clicks. However, I’d say plugins are far better at responding to these types of issues now. Supertone Clear, for example, is very good at supressing these in a natural way.
Variable Background Noise
Things such as rustle, wind and electrical interference I would consider to be variable or sporadic noise. These are usually the hardest types of sounds to suppress in a discreet manner and, depending on the severity, may not be possible to completely removed.
Reverb
De-reverb-ing (?) or de-reverberation is another area which has hugely improved recently, and these types of plugins can be used to great effect when applied in moderation. This processing will reduce the audibility of early reflections (sound bouncing off nearby surfaces) and can make dialogue tighter and clearer.
Application
Before diving in, it’s good to think about what specific issues you want to treat. It’s then generally a good idea to treat each issue separately, rather than hoping one plugin will fix everything.
Taking a trial-and-error based approach will generally work best when applying noise reduction. Some plugins will work well with certain sounds, but then can be irresponsive to others or create audible artefacts or robotic-ness.
Another tip to remember is that sometimes piggybacking one plugin onto the next and applying light processing with each will be more effective and smoother than going in heavy handed with one plugin.
Is Perfection the Goal?
The advancement in noise reduction brings with it a philosophical question. How much of the location do you actually want to hear? It’s now quite easy to create a completely dry dialogue track devoid of any background noise or location nuance whatsoever. But is this really the goal?
Generally, I’d say extreme application is rarely appropriate as if the dialogue loses all sense of space, it can become unnatural and soulless. If you strip all background noise from one clip of dialogue, you can then get into a situation where you have to match it to other dialogue tracks and therefore end up removing all the background noise from these too.
Beyond Noise Reduction
One of the real advancements we’ve seen recently has been the development of dialogue restoration plugins. These not only apply noise reduction, but can actually help improve the quality of the dialogue by reintegrating missing frequency components and recovering previously unrecoverable dialogue.
One such plugin by Accentize is called DX Revive which I’d highly recommend. The Adobe Speech Enhancer also provides a similar offering for free, but with less control over parameters. So, if you really get stuck, these are well worth a look.
Up next time we’ll take a look at some other plugins available.
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