All You Need To Know About Room Tone
When we record dialogue in a space we capture a combination of the principal sources and the accompanying ‘room tone’. The space still colours our sound recordings even if we’re using a well treated space and close miking our subjects. However, when we come to edit our dialogue it’s not unusual for sections to get moved around resulting in gaps. If we attempt to mixdown our final audio track like this, the gaps will sound unnatural. The solution is to record a specific room tone snippet during the production process. This adds very little time to the location recording process and will save lots of time in audio post production.
Room tone is specific to the space you’re working in. Very importantly, it’s also not simply the space when empty. Equipment, props and people will all change its character. Because of this, the aim is to capture the room tone with people and equipment in position, though preferably with them stationary and silent.
Next up, don’t confuse room tone with room ambience. Although you could use the room tone for ambience, typically the room ambience track forms part of the effects tracks rather than dialogue tracks.
Sometimes our location is quiet and has a dead acoustic, but don’t assume that the room has no sound, or that room tone from such a space won’t be useful. Often, in areas of exposed dialogue, room tone can be obvious even if it’s not very invasive. This is often increased by additional post production processing such as EQ and compression. So if possible, always record room tone.
We typically use room tone to even out and fill gaps in the audio mix on dialogue tracks once the dialogue edits have been made. You might wonder why we don’t simply copy around sections in between existing dialogue. This can certainly work and shouldn’t be ruled out if the gaps are nice and clean without any unwanted noises. However, in reality, audio post production is simpler and quicker if you have a consistent prerecorded room tone track. What’s more, the job at the production stage is to think ahead and be covered for various requirements later on.
Finally, if you have to pass your production audio to someone else to finish off, having proper room tone tracks will make their job considerably easier. This will make your results better and you more popular.
Room tone provides a flexible background that should be easy to combine with your location or production sound to even out edits, standardize levels and deliver a polished, natural sounding result. It can also be handy as a source to define a background noise profile for noise reduction processing. Let’s look at how we actually use it in two different post production tasks.
It’s easy when editing and repositioning the dialogue elements of your audio track to end up with gaps, and the simplest and most common use of a room tone track is to fill these gaps. Simply line up sections of the room tone track to fill the gaps. Next make sure the levels sound consistent. Most video editors provide individual clip level adjustment, and this is usually much quicker and works better than linear automation. Finally, if available use small audio crossfades to ensure there are no nasty clicks where the sections join.
it’s not uncommon to replace sections of dialogue after shooting (ADR). This dialogue will probably be recorded dry in a vocal booth with one mic, and will not immediately match the other dialogue audio. Here we need to add room tone to all the ADR dialogue sections and in the gaps between. To create a continuous track of room tone copy round sections and crossfade the joins. To complete this task use EQ to match the dialogue sound and also add reverb to the ADR to match the original space.
If you want your audio track to sound consistent then you need to capture room tone in each location you record in. In fact, to be pedantic it will change every time you move your microphones or adjust their gain, so bear this in mind and decide if you need to recapture the room tone more than once.
For your room tone to work seamlessly in audio post-production it’s important to capture all the mics you are using in their respective positions. The best time to do this is immediately after you have set your peak gain levels and just before you shoot. Remember, tell everyone you’re capturing room tone and ask them to stay where they are and be quiet while you do it. Record at least 30 seconds (1 minute if possible) as this means you won’t have to loop sections in post production.
Finally, as a variation on this set up, if there is a persistent background noise that you are recording in your production audio (such as a fan) and this is something which you are planning on removing in post production using clean up or restoration plug in, you could follow the procedure above but with the device switched off. This will give you an additional cleaner room tone to work with.
If you forget to record room tone, or you’re given production sound with no room tone track, then you can hunt for gaps between the existing dialogue. It sounds easy and if there are plenty of pauses in the dialogue you may be in luck. But you’ll need clean sections without unwanted noises, and the process of copying and looping is time consuming and not always successful.
Audio editors often use sample libraries to finish the effects component of a production, but you can actually head to the library for room tones as well. These will be properly prepared, be plenty long enough, and with a little EQ can often patch up your dialogue track to an acceptable standard.