MATRIZ LÓGICA DEL PLAN DE MANEJO AMBIENTAL

Before we discuss hooking things up and troubleshooting, let’s cover each of the basic capturing tools in greater detail. To create a sampled instrument, you need a sound source and something to capture the sound source. There are two primary methods to capture the source: one involves a microphone and the other involves a direct input method. A microphone is a transducer that converts acoustic energy into electrical energy. The direct method accepts sources that are already electrical and does not convert the signal. The direct method might be easier in terms of recording, because you can connect the source directly to the sampler with one or two cables (one for mono and up to two for stereo), and then you can immediately record. For other sources, you need to set up a microphone and capture the acoustic sound from the source. The method you use depends on the sound source. Some sources cannot be recorded by a direct method because they do not have an electrical output. For sources such as acoustic guitars, if they also have magnetic pickups, you can capture using either a microphone or a direct method.

For an excellent book on microphones, see John Eargle’s The

Microphone Book (2nd edition, Focal Press, 2004). It is amazing

that nearly 400 pages can be written on a single subject such as microphones. This gives you an idea of just how complex the topic really is. Our discussion here takes a much simpler approach. The basic types of microphones are dynamic, con- denser, and ribbon. Each type works in a different way, with different strengths and weaknesses. You should take your project goals into consideration when choosing which micro- phone to use. While it is possible to pay thousands of dollars for a single microphone, you may be investing too much; a

Making Connections

hundred dollars may buy something that would work just as well or better for your specifi c application.

Instead of describing each type of microphone in detail, this section includes some basic information that will help when using a microphone to record your samples. As many have learned from experience, it is diffi cult to fi gure out in advance what the most suitable microphone for your use may be. Regardless of whether you use only the microphones you own or whether you rent very expensive microphones, until you hook them up and listen to the results, you cannot be sure what will work best. You might be able to make an edu- cated guess because the different types of microphones have specifi c traits that are consistent, but sometimes it turns out differently than you expected.

2.3 Using microphones

2.3.1 Power

When hooking up a microphone, you need a microphone, a cable, a preamplifi er, an analog-to-digital converter, and either a hardware sampler or an audio interface for your computer. If you are using a condenser microphone, you need to have a power source (Figure 2.3). This power can range from +1.5 volts DC to +48 volts DC (direct current). Electret condenser microphones may have power supplied by a small battery built into the microphone. It is essential that you follow the specifi cations for the voltage and polarity of these batteries. If the voltage for the microphone circuit is supplied by the power supply of your recording console, it is called phantom power. The phantom power voltage is dis- tributed over two of the conductors of your basic balanced microphone cable (see Sections 2.10 and 2.11 on audio cables later in this chapter) with the audio signal. This DC power does not interfere with the AC (alternating current) of the audio signal. Not all professional microphones use the stan- dard +48 VDC power specifi cation. The proper power voltage is normally identifi ed by the manufacturer. Follow the speci- fi cation of the manufacturer to ensure there is no damage

Audio Sampling

caused to your microphones. Do not apply phantom power to ribbon microphones. The delicate ribbon material can be damaged.

2.3.2 High pass fi lter

Many microphones have additional features that provide extra value and fl exibility. These include a high pass fi lter, a pad, and a variety of polar patterns. A high pass fi lter allows high frequencies to pass while attenuating low frequencies (Figure 2.4). This is useful for eliminating unrelated low- frequency noise, reducing the sound caused by vibrations and bumping the microphone stand, and reducing the prox- imity effect. The proximity effect is a boost of lower frequencies and exists in situations where a sound source is close to a directional microphone. The result is a boost in the amount of bass.

2.3.3 Pad

A pad lowers the electrical output of the microphone (Figure 2.5). This can be useful when capturing loud sounds. A pad might be used while recording drums, electric guitar ampli-

Figure 2.3 Tube Microphone

Figure 2.4 Filter Switch.

Figure 2.5 Pad Switch.

fi ers, and other loud sound sources. Using a pad is very important when the sound source is loud enough to cause clipping and distortion at the microphone’s output. With the pad engaged, any clipping and distortion will be avoided. Keep in mind that certain sounds can still be too loud and might cause clipping before the pad phase of the microphone. In this case, lower the volume of the sound source or increase

Audio Sampling

the distance between the source and the microphone. Many preamplifi ers and audio consoles also have pad switches.

2.3.4 Polar patterns

A polar pattern describes the directionality of a microphone (Figure 2.6). There are three primary polar patterns and several others that are related to the fi rst three. The primary patterns are omnidirectional, bidirectional, and unidirec- tional. The other types (hypercardioid and supercardioid) are subcategories of the unidirectional pattern. The omnidirec- tional pattern captures a pressure reading of a specifi c point in the air without regard to the direction from which the sound comes. A bidirectional pattern captures a differential pressure reading using a diaphragm that is open on two sides. It receives sound from two directions and has reduced reception coming from the sides. The unidirectional pattern captures a cardioid (heart-shaped) pressure reading from the front of the microphone. A unidirectional microphone can either be the result of combining an omnidirectional pattern with a bidirectional (fi gure-eight) pattern or can be created through the use of specifi c design features of the microphone’s encasement (see Eargle’s book listed in Section 2.2 for more

Making Connections

on this). The other unidirectional subcategories are created either through different omnidirectional and bidirectional combinations or through a variety of different physical designs.