Audio Repair 101: Reverb in Audio & Video Recordings
A Comprehensive Guide on Audio Repair: dealing with Reverb
Sound is not an easy thing to control. The second it's created, it travels in every direction, bouncing off everything it meets. This chaos is known as reverberation. In your recording, excess reverb can be distracting. Yes, there is an artistic element that can make it very appealing from a music standpoint. Many artists use reverb on their instruments and voice to give added character. When it comes to a dialogue, clear speech becomes much more valuable. This is always true unless the reverb tells your audience something about the environment.
To convey clear information to our audience, we first have to understand how reverb forms. Then, knowing how it forms, we can begin discussing how to remove it. We will go through this process in a very specific order. The first step is to change the environment to reduce reverb. Next, we can adjust our equipment choices. Last but not least, we will discuss our options in post-production. It's important to follow this order to achieve the highest level audio quality with the resources available to you. If you're having trouble managing reverb in your recording, don't feel bad! This is something that everyone from the Podcaster to the experienced Sound Engineer has to deal with. Thankfully, there are many, simple methods of reducing its effects. When you've learned them, you can approach almost any environment with the confidence to come away with a good sounding recording.
Reverb: Early & Late Reflections
Let's begin by examining the elements of an environment that contribute to reverb. As I've said, reverb is the reflection of sound off a surface. When you step into a room that has a lot of reverb, you first hear the direct sound. Then, for a period of time you hear the reflections as they continue to bounce off walls and objects around you. The sound then trails off as the traveling vibrations lose energy.
What makes one room create more reverb than another? The presence of hard, flat surfaces are excellent at reflecting sound. The opposite of these surfaces will not reflect sound well. In this case, that is a good thing. Soft, irregular surfaces tend to absorb sound and reduce reverb. For example, a room with hardwood floors will have much more reverb than a room with carpet. Another thing that contributes to reverb is room size. In this case, the size of the room has less to do with the intensity of the reverb and more to do with the length of time that it continues. A large hall will produce a reverb that can last several seconds, and a small room can be less than one. The reason is that the sound has a longer distance to travel before reflecting off the surfaces of the room. Sound travels fast, but it is slow enough that a small difference in room size can make a noticeable difference in duration.
Dealing with Reverberation
So, does this mean that you can only record audio in environments that have little to no reverb? Of course not! There is still hope for people who have found the perfect space to film or record that isn't ideal for audio. Sometimes, it can be as easy as grabbing some carpets or bed sheets and covering the floor or an off-screen wall. Even the common objects in a room like bookshelves or furniture play a part in reducing reverb. This is the most practical way to fight reverb in a pinch, but it's not the most powerful way to acoustically treat a room. There are foam-like materials made to absorb sound more than a carpet. These types of materials are often used to line the walls of recording studios where the control of sound is most important. This material can also be used to pad the inside of a microphone shield. These devices mount onto your microphone stand and form a shell behind the microphone. Since this is a bulky microphone set up, this solution is more geared towards those who are just recording sound.
After you've adjusted your environment, the next step in the process is to examine your equipment. The most important consideration here is the polar pattern of your microphone. While polarity pattern sounds like something complicated, it's quite simple. Everyone, at some point, has cupped their hand behind their ear to listen closer to some source of sound. We do this to block out noises coming from other directions so we can focus on a sound from a specific direction. Microphones can do this as well with their polarity pattern. An omni-directional pattern accepts sound from every direction. This makes it open to all the reverberations happening in an environment. By switching to a cardioid pattern, you now can limit the sound accepted to the direction the microphone is pointed. You can even further limit the reverb by pointing the microphone towards a wall or area that has the best sound absorption. Whatever reflects off that surface will be less than noticeable than others.
It is also acceptable to use two different microphones at the same time to take advantage of their different properties. A lavalier/boom microphone combo is a classic technique for many videographers. The lavalier, which is small and often attached to a person’s clothes, provides the basis for the recording. The sound captured here will have much less reverb than a room microphone because it is so close to the sound source. Then, to give the recording a much more natural sound, balance it out with a recording from a boom microphone. These are typically hung off screen and will sound more natural because they are placed at a normal listening distance. By using both recordings, a nice balance can be created that will also minimize the amount of reverb that would be heard from just one microphone in the room.
How To Restore Reverb in Audio / Video Recordings
Only after taking these steps should you move on to post-production. Post is not the ideal place to fix problems in a recording, but there are a couple of tools we can use. The first one that is very effective is Automatic Dialogue Replacement (ADR). This dialogue replacement is done by recording new dialogue after the footage is captured. The advantage of this is being able to record in a controlled environment. With this method, even the worst environments can be presented with nice, clean dialogue. This is no cheap trick either. All the way up to the highest levels of video production, ADR is being used to deliver quality results. While it has its advantages, it does have a major drawback. Syncing the new audio to the lips and actions of your actors/actresses is incredibly difficult. The timing, tone of voice, and the expression all have to match. Pulling this method off takes a great deal of skill on the part of the actor or actress.
The other post-production option involves editing the original audio to remove the reverb. Audacity is a software that most people in the world of audio are familiar with. It provides free access to many useful tools that you can use to shape and refine your audio. Reverb happens to be one of the more complicated problems to fix. Within Audacity, you can equip a noise gate to chop off the quieter tale-end of the reverb which will leave the main audio untouched. Next, you can experiment with an equalizer and try to reduce the resonant frequencies which reverberate more than others. Lastly, you can go from transient to transient and increase the fade in volume after the direct signal ends.
These methods, even done well, will not reduce anything more than subtle reverb. The ERA Bundle comes with a tool that does all this. I tested this, myself, and it honestly did a much better job than I was able to do on my own. With the touch of a button, the reverb tool was able to greatly reduce the reverb in the sample recording I took. After taking all the right steps to reduce the reverb before recording, this tool can finish the job well in the post-production stage.