|
The selection of microphones would also depend on the type most suitable for our use. The two broad categories of microphones are the dynamic and condenser types. Most microphones available in the market are either of these two types.
Dynamic The moving coil microphone, shown in Fig. 7.3(a), or the dynamic microphone has a flexible mounted diaphragm coupled to a coil of fine wire. The mount is such that there is an air gap between the coil and a magnet. When sound hits the diaphragm, the diaphragm surface vibrates in response. This diaphragm motion extends to the coil, which moves back and forth in the field of the magnet. As the coil cuts through lines of magnetic force in the gap, a small electrical current is induced in the wire. The magnitude and direction of that current is directly proportional to the motion of the coil, and the current thus is an electrical representation of the incident sound wave. Typically its frequency range is between 40-16,000 Hz. Dynamic microphones are rugged and robust, and are mostly used in field situations where the emphasis is not exactly on the fidelity of sound but the sound itself. They are also built to avoid rubbing sounds from the user's hands. The microphones that are used by rock stars are normally of the dynamic type.
Condenser Said to produce very high quality of sound, condenser microphones are also called electrostatic microphones; see Fig. 7.3 (b). A light flexible metallic membrane is stretched close to a flat metal plate. Due to the varying space between these plates by the sound wave pressure· fluctuations, the capacitance is altered. Variations in current required to recharge the changing capacitance constitutes the audio signal. Typically, the frequency range of these microphones is between 20-18,000 Hz. Unlike dynamic microphones, condenser microphones need an external power supply. Some condenser microphones have a battery attachment on the cable as part of the connector. Others need power delivered to them through the microphone cable itself. it is When power is supplied to the microphone through the connecting cable from the recording instrument itself, known as phantom power supply. Phantom power supplies are available on some audio mixers You just need to plug in the condenser microphone, and the mixer provides the required power. Owing to their sensitivity, condenser microphones are normally used in studio recordings and for sound effects where the emphasis is on fidelity of the sound recorded. The sensitivity of these microphones enables them to pick up even faint sounds, though the surroundings must be kept as quiet as possible for recording.
Electret capsule This is a miniature condenser microphone incorporating a plastic film diaphragm with an inbuilt permanent electrostatic charge. It does not require a polarizing voltage. Since not dependable, these are hardly used in video production.
Pick-up Patterns
Mics can be classified according to their directional sensitivity or pickup patterns, as well as their transducer elements.
Different recording situations require the use of mics that pick up sounds form a very narrow or a very wide area.
Some mics pick up sounds coming from every direction, whereas others are sensitive to a very restricted area. The three basic categories of pickup patterns are as follows: omnidirectional, bidirectional and unidirectional or cardiod.
The choice of a microphone also depends on the manner in which they pick-up sound. One does not use the same microphone to record atmosphere sound outdoors and also record interviews. Each situation del1Jands a particular pick-up pattern. Although there are a number of. varieties based on pick-up patterns, the following three serve our purpose.
An omni-directional microphone can pick up sound from all directions irrespective of its point of origin. It is very easy to use and is preferred to pick location sound.
A uni-directional microphone can pick up sound only from one direction. You may have noticed in music shows that even though instruments are placed close to each other, the microphone placed above one instrument does not pick up sound from another. Uni-directional microphones are best used for vocalists and musical instruments. They are also widely used for recording in outdoor interviews and in panel discussions in studio situations.
A bi-directional microphone can pick up sounds from the front or the rear, but does not respond to sounds from the sides. However, it is very sensitive. Distance between the source of the sound and the microphone is critical because bi-directional microphones tend to produce pops when not placed carefully. Bi-directional microphones are best avoided for outside work but a couple of them can be used for discussions that have a group of four or five in studio situations. They also come in handy when two persons are seated across a table for an interview.
A multidirectional mic is constructed with more than one pickup head aligned to receive sound from different directions. Such mic may contain as many as six heads placed for simultaneous recording of 5.1 audio mounted in one fixture. The mic combination may be mounted directly on a camera or any other mic mounting system. The danger of using such a mic comes from any equipment noise near the mic being picked up by more than one head increasing noise levels.
Microphones also come in different shapes, sizes, and combinations. For example, a microphone could be dynamic but uni-directional or condenser but omni-directional. The most commonly used hand-held microphones are either the dynamic or condenser types. Hand-held microphones are placed on stands for stability. The sensitivity with which a microphone picks up sounds depends not only on whether it is a dynamic or condenser microphone, but also on the pick-up pattern. Like mentioned earlier, the choice of a microphone is made well before the actual recording.
Some commonly used directional mics are "as follows.
Boom mics These are used to record location sounds and dialogue in fiction shoots. In fiction, the dialogue thus recorded is later dubbed in a studio. Boom mics are normally placed at the end of a long pole and can be moved up or down without being seen in the frame. Figure 7.5{a) shows a boom mike, which can be used with a boom pole that can be extended or shortened as required.
Lavelier mics Also called lapel mics or button mics, a lavelier mic, see Fig. 7.5{b) is normally pinned to the interviewee. It is a small condenser mic and can either be corded or wireless. The wireless types are preferred when movement of the subject is required. The wireless mic version runs into a transmitter, usually worn on the belt. Lapel mics can be powered by batteries or phantom power, depending on the make.
Mono and stereo mics When audio is mono-aural it can only indicate differences in quality and volumes. However, stereo audio can also indicate the direction of the sound. Mono-aural sound can be very flat, unlike stereo
Sound that is very rich because it indicates direction. Care should, however, be taken to match video with sound perspective, movement (called audio panning), and the amount of noise. A stereo mic, see Fig. 7.5(c), is essentially: lwo-mic-in-one unit. Stereo mics are often expensive and come in professional models.
|
Participants