Audio systems can have a limited range of volume, referred to as the dynamic range, which they are able to handle. Sound signals can get deteriorated if the sound is too loud because it can create distortion overload. When the sound signal is very quiet, there can be problems as well. For instance, sounds that are wanted can end up combined or lost with the noise of the background. They can be caught in the ventilation system sounds, the sound of tape noise, or other sounds of similar volume.
Both over-modulation, which is when the signal is over-amplified, and microphone overload, can easily exceed the limits of the audio system. One way the microphone can easily be overloaded is if it’s in close proximity to a loud noise source.
On the other hand, under-modulation (audio signals that are too weak) must also be prevented. One way of doing this is to make sure to use enough amplification, and have the microphone near to the sound source. In addition, be careful not to hinder the original source of sound’s dynamics.
Background on Acoustics
It’s easy to understand sound when you consider the difference between what you hear in a room full of furniture or people, compared to a room that is completely empty–different sounds entirely. A basic understanding of general acoustics is the first step to overcoming the larger amount of audio problems you may encounter while in production.
Acoustics that are chosen very carefully can ensure that the larger amount of television, along with audio studios, don’t sound overly “dead” or overly ”live.” Both the impression of spaciousness and of vitality can be conveyed by sound being strengthened and enriched through reverberation.
It’s important to understand, and many people will notice, that as conditions in the environment change, so can the way sound is absorbed and/or reflected. With the addition or removal of furnishings, the quality of sound can either be well-defined (brightened), or dull (dampened). For instance, the sound in a theater that is full with an audience, or of empty seats, is very remarkable. Sound quality can become hollow, boxy, or harsh depending on the placement of items, such as an oversized scenic flat; this is especially true when considering the height of the ceiling, or the size of the setting.
Hard surfaces such as metal, glass, plastic, stone walls, or tile absorb little sound and will reflect the sound nearly as loud as what it originally was
. In addition, frequencies which are higher benefit from this kind of reflection, creating a sharper, brighter sound.
Soft surfaces, which include rugs, curtains and couches, will absorb some of the sound waves into the material; notes that are higher are more readily absorbed. This means that the sound will lack in the frequencies that are higher, and the result will be a quieter sound. This sound will be somewhat muted, even mellow, and perhaps dull. There are some materials that are so good at absorbing, sound will be minimally reflected.
Multiple surfaces that are large, such as a churches, halls, or bathrooms, can create a space that is very reverberant, which is often referred to as “live”. Waves of sound will rebound off a surface to another with such ease, that both the version reflected, as well as the original, can be intermixed and easily heard. In these situations sound quality undergoing many changes can degrade clarity significantly. .
In the situation where extremely reverberant surrounding
s are involved, the reflections can be heard just mere seconds after the actual sound has finally stopped; for some instances it can even create an echo that is repeated. The microphone’s position, the sound’s quality and pitch, the source of the sound’s position, and the space’s design, all go into determining whether or not the sound is either rich, or confusing and unpleasant.
The Breakdown of Acoustics
Reflections can be reduced if the surroundings are overly live by:
- Addition of acoustic panels
- Addition of rugs which are thick
- Addition of cushions
- Draping of blankets on chairs and frames
- Furniture that is upholstered
- Thick curtains where available (closed)
- Microphone and sound source moved close together
If there is a need to have acoustic reflections increased because the sound is too dead:
- Addition of reverberation that is artificial
- Removal of cushions
- Removal of rugs
- Removal of any furniture that is upholstered
- Addition of panels for the floor (fiberboard, wood)
- Curtains that are open to increase open surface space
- Microphone placed further from sound source
- Addition of panels that are plastic or board for the surface area
When the sound is being created in an area that is full of absorbent surfaces, the reflected sound and the original sound will be quite muffled. The conditions in this situation are termed “dead” and sound that is direct will get heard with surrounding reflections that are relatively few.
In this situation, even noises that are loud (gunshots and handclaps) aren’t able to carry overly far before they quickly die. In open areas, such as outside, sound is often quite dead. The reason for this is that air can be very good at sound absorption. Also, with few surfaces capable of reflection, sound will quickly die.
All of us have heard sounds outside that are dead. Sound is weak in the open air because it cannot travel very far; it is quickly absorbed by air because of the low amount of surfaces that can reflect it. In this situation (in particular when people are quietly speaking), the microphone will need to be even closer than usual to the subject.
The sound produced in the open air has a quality to it that is quite characteristic and can be recognized quickly. Part of what is notable comes from the fact that sound isn’t reflected and lacks bass and top. In the studio it can be difficult to recreate convincingly, even if acoustic panels that are highly absorbent are used to surround the subject completely.
Be aware that there can be problems when the mic is placed in too close a proximity. . In this situation the sound can be coarser, and there will be an over-emphasis of bass. Letters like B, P and T can sound like explosive blasts; the letter S will be severe, and breathing will be highly audible. The sound of teeth clicking together will even be highly audible. In the instance of close instrument placement, noises that are mechanical will be overly revealed such as a scraping bow or a key clicking.
The placement of the microphone is often influenced by the acoustics. If the mic is placed near the subject in relative close proximity, much of the reflections that are unwanted in a surrounding that is live can be avoided. Surroundings that are dead won’t allow the sound to carry adequately; therefore, a close mic is necessary. This is particularly true if the surroundings happen to be noisy. A mic that is placed closely can help keep voices heard above other unwanted sounds.