Basics of Video Sound

Des Lyver

• Publisher: Routledge
• Year: 1999
• ISBN:
  9781136118777
• Edition: 2
• Topic: Tecnologia e ingegneria
• Subtopic: Ingegneria acustica

Now fully updated to reflect the latest advances, the second edition of Basics of Video Sound is a primer for anyone wishing to learn about recording sound. It describes the principles and processes involved in obtaining professional results in educational, training and corporate environments. Assuming little prior knowledge, this book covers everything from how to choose a microphone and obtain the best quality recordings, to editing the results for the final screening. It features:
· the latest advances in the use of disc and minidisc systems, computer based editing in audio post production
· coverage of studio and location work
· descriptions of the role of each crew member
· full explanations of technical terms
· health and safety precautions
· practical advice on the equipment available and how to use itBasics of Video Sound aims to provide the reader with a rapid understanding of what is actually a complex process, without getting too bogged down in technical terms. It is equipment non-specific and references to technical matters are only included where necessary to understanding, for example a short explanation of the electricity and physics that is needed in order to become a good sound recordist.

1 Sound and video

DOI: 10.4324/9780080499949-1

‘In the beginning there was silence’

The sound teams

The sound team will be led by the sound supervisor who may have a number of sound assistants. The sound supervisor will be responsible for the overall sound output but may be helped by a boom supervisor who will work with the sound team on the studio floor operating microphones fitted to the sound booms.

For location work there will still be a sound supervisor, but the role will be different. The sound supervisor may work alone to record the location sounds, which are then passed to a dubbing mixer and post-production sound team who put all the sounds together at the editing stage.

The studio sound team

It seems to be stating the obvious to say that the sound team’s job is to get the performers’ voices, from the floor, and mix them with any music, or sound effects. This may come from any source that is commonly used to store sounds. These include synthesizers, CD, tape, disc-based or digital systems. These sounds are normally blended with the microphone sounds, using a mixer, in real time adding them to the pictures to make the programme which is recorded onto video tape.

This is indeed the sound supervisor’s job, and to do this he, or she, will normally work in the gallery area with a range of source machines, sound processing devices and a mixer. The problem is caused by taking it for granted that a microphone will pick up the sound we want and that mixing it with music, or sound effects, will create the effect we want.

The sound team needs to work together to produce an overall sound that is not only acceptable but is also realistic, and at the same time does not interfere with, or conflict with, the picture that has been selected.

To achieve acceptable results the sound team needs to know how sounds behave, how microphones work, how to correct any differences in quality resulting from inadequacies in the microphones or associated equipment and how to balance the levels to produce a natural sound. Often it is not so much a question of ‘what’s the answer to the problem’ as ‘what definitely will not work and what might’. This leads the team to consider a number of possibilities, all of which may work, from which one possibility is selected more on personal experience and preference than because ‘that’s what the book says’.

The location sound team

The make-up of the location sound team is led by demand. Obviously someone must be responsible for sound, but how big is the team?

It is possible with modern camcorder equipment to make the sound person the equipment itself. All you need is a microphone built into the camcorder, some form of automatic control over the recording level and sound, of sorts, will be recorded in synchronization with the pictures. Anybody who has tried their hand at the ‘and the camcorder came too’ type of holiday will recognize the simplicity of this system. They will also realize the disappointment it can cause.

It is equally possible to take a portable mixing desk, a range of outboard equipment, several microphones, boom operators, timecode generators and portable DAT tape recorders to recreate a situation as close to a studio environment as you will ever see.

On location we shoot out of order, with a minimal crew, and then carefully edit everything together to form the linear programme. Once the picture track has been finished there is really no reason why the audio can’t be mixed, edited and added to if necessary. This stage is called post production which we will look at in more detail later.

There are only two types of sound that need to be recorded on location. A sound supervisor might sum it up by saying ‘Get me good, clean, sync sound and lots of buzz track’.

To sum up, it is really a question of what is required in the way of location sound, and what can be added later, that will dictate the make-up of the sound team.

What is sound?

In order to make the very best recordings, it is important that we understand what sound actually is and how it behaves in different environments. The key difference is whether the environment is closed or open – indoors or outdoors.

In simple terms sound is thought of as movement of air caused by a vibrating body, but it is actually a little more complex. Three basic elements are needed to create a sound:

1. A vibrating body
2. A medium (for the vibrations to travel in) and
3. A receiver (to convert the vibrations into a useable form).

It is essential for good sound recording that this is thoroughly understood. We tend to think of sound as something we can hear. There are many sounds that a receiver other than the ear, a microphone for instance, can ‘hear’ that we cannot. One simple example is the wind.

Figure 1.1 shows the simple case of someone speaking (caused by the vocal chords vibrating the air which comes out of the mouth), the vibrations moving through the air and the ear receiving the vibrations.

Figure 1.1

Figure 1.2

Figure 1.2 demonstrates a more complex concept. Two tin cans are joined together by a length of string and a pencil is being used to tap the tin causing the molecules in the tin to vibrate (vibrating body). The vibrations travel along the string (the medium), until they reach the other tin, which vibrates. If a person places their ear against the tin, these vibrations now vibrate the ear (the receiver) directly and the sound is ‘heard’. The vibrating body and the medium are different.

Figure 1.3 shows a classic example of misunderstanding sound, which could result in a poor sound recording. A tape recorder is placed on a table and its motor is vibrating. This vibration is transmitted to the table, which in turn vibrates, the table’s vibrations are transmitted to a microphone stand, which also vibrates. These vibrations move on to the microphone which faithfully reproduces them along with the vibrations it is receiving through the air, directly from the person’s voice. Here there are two vibrating bodies and two mediums picked up by one receiver. If the ear is placed directly on the table the vibrations from the tape recorder can be clearly heard. Placing the ear on the surface supporting a microphone stand, and listening for these possible unwanted vibrations, is a good habit to get into.

This last example leads us to think about something else which is often misunderstood – noise. If we need a definition of noise it must be any unwanted sound. If we know what causes sound, we can begin to eliminate noise. Removal of any of the three elements would result in no sound transmission. In our example, taking the tape recorder away and putting it somewhere else would remove the vibrating body causing the noise. Equally, moving the microphone away from the medium (the table) would cure the problem, by removing the receiver of the noise.

Figure 1.3

So far we have only looked at what sound actually is. We do not need to understand technicalities such as frequency, wavelength and loudness in order to record the sounds we want and eliminate the ones we don’t.

Sound outdoors

To achieve good recordings it is necessary to understand how sound behaves both outdoors and indoors. We will take the example of voice as a vibrating body, air as the medium and the ear as the receiver.

Air is an elastic medium under pressure (atmospheric pressure). Outdoors the voice vibrates the air around it (Figure 1.4) causing it to move (vibrate) and these vibrations travel outwards rather like the ripples on a pond do when a stone is thrown in.

Figure 1.4

Like the water in the pond, the air tries to resist the vibrations and hence they get weaker with distance until, eventually, there is no more vibration. Equally the vibrations move outwards at a specific speed.

It is obvious, but important to understand, that the vibrations will be at their strongest close to the source. The greatest sound level is, therefore, as close as possible to the source. It can also be seen that there is a point where there are no more vibrations and it follows, no more sound. If the receiver was a microphone, then it should be placed as close as possible to the source.

The speed the vibrations travel at is known as the speed of sound and, in air, is dependent on the atmospheric pressure. Generally the speed can be taken as 330 metres/second (m/s) which, compared with the speed of light, is very slow. Think, for instance, of a cricket match (Figure 1.5). The ball can be seen to be struck before it is heard. This leads to a synchronization problem which, in this instance, we have learnt to accept.

Figure 1.5

Sync problems

If you watch a film on television, it is very noticeable that lip sync has been lost if there is only a very small gap between the lips moving and the sound being heard. This can be as little as two or three frames, equivalent to about 1/12 th second. At 330 m/s this translates to a distance of about 25 m.

It is often the case that because of the position at which microphones are placed, the strength of the vibrations aren’t great enough to give acceptable sound. There are three solutions:

1. Move the microphone closer
2. Increase the strength of vibration (make the sound louder)
3. Dub the sound on later

Something we will look at in greater depth later is that it is very rare to have this simple state of one vibrating body, a medium and a receiver. Normally the crew, traffic, wildlife and aeroplanes are all vibrating the air (Figure 1.6). Depending on the distance and pressure of vibrations, these may produce an unacceptable level of ‘noise’.

Figure 1.6

Understanding the problem leads to finding the answer. If we can place a microphone such that it receives stronger vibrations from the wanted source than the unwanted source, the wanted sound will appear louder (or in the foreground) and we will have gone a very long way to reducing the interference from what we call ‘background’ noise.

Outdoors, the main problem with recording sound is being able to get the microphone close enough to the sound we want. Sometimes the sound ...