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Post Index » STAGE TECHNIC » Pro Sound


Media College (Chương 1 : Âm Thanh) (7,8) - Page 4 PDF Print E-mail
Written by tuyenphuc   
Thursday, 18 March 2010 10:57
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HOW TO USE MICROPHONES

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This tutorial aims to provide you with the skills to choose the correct microphone and use it properly to obtain the best possible sound. It is suitable for people interested in any type of audio or video work. Before you begin you should have a basic understanding of the most common types of microphone and how they work. If you don't, read how microphones work first.

The tutorial is six pages and takes about 20 minutes to complete.

Introduction

The microphone (mic) is a ubiquitous piece of equipment. Found in everything from telephones to computers to recording studios, microphones are part of our daily life.

Few people think about the microphone in their telephone when they use it. Some people think about the microphone on their video camera when they use it. All professionals pay careful attention to their microphones whenever they use them.

Don't make the mistake that many amateurs make and use whatever mic is at hand (e.g. using a vocal mic for a bass drum). Also, don't make the mistake of assuming that using a microphone is easy. Microphone technique is a learned skill - plugging it in and pointing it isn't always enough.

The microphone is perhaps the most critical part of the audio chain (assuming that all other components are at least acceptable quality). A good quality microphone will provide you with the basis for excellent audio, whereas a poor quality microphone will mean poor quality audio - no matter how good the rest of the system is.


Choosing the Right Microphone

As we discussed in the previous tutorial, there are many different types of microphone in common use. The differences are usually described in two ways: The technology they use (e.g. dynamic, condenser, etc) and their directionality (e.g. omnidirectional, cardioid, etc). In addition, microphones have a number of other characteristics which need to be taken into account.

When choosing a microphone, the first thing you will need to know is what characteristics you need. After that, you can worry about things like size, brand, cost, etc.
Note:
If you haven't done so already, you might like to do some groundwork and read how microphones work first.

Things to Consider

Work through each of these characteristics and determine your needs.

Directionality

Decide which type of directional pattern best fits your needs. Remember that it's usually better to use a less directional mic in a position close to the sound source, than to be further away using a hypercardioid. For more information see microphone directional characteristics.

Frequency Response

Make sure the mic's frequency response is appropriate for the intended use. As a rule of thumb flat response patterns are best, but in many cases a tailored response will be even better. For more information see microphone frequency response.

Impedance

The rule of thumb is: Low impedance is better than high impedance. For more information see microphone impedance.

Handling Noise

Remember that the diaphragm works by converting vibrations from sound waves into an electrical signal. Unless the microphone has some sort of protection system, the diapragm can't tell the difference between a desirable sound wave vibration and any other sort of vibration (such as a person tapping the microphone casing). Any sort of vibration at all will become part of the generated audio signal.

If your mic is likely to be subjected to any sort of handling noise or vibration, you will need a mic which will help prevent this noise from being picked up. High quality hand-held mics usually attempt to isolate the diaphragm from vibrations using foam padding, suspension, or some other method. Low quality mics tend to transfer vibrations from the casing right into the diaphragm, resulting in a terrible noise.

Note that lavalier mics don't usually have protection from handling noise, simply because they are too small to incorporate any padding. It is therefore important to make sure they won't be moved or bumped.

Purchasing a Microphone

If you can afford it, it makes sense to buy a range of microphones and use the most appropriate one for each job. If your budget is more limited, think about all the different things you need to use the mic for and try to find something which will do a reasonable job of as many of them as possible.

  • For vocalists a simple cardioid dynamic mic (such as the Sure SM58) is a good starting point.
  • For video makers, a useful option is a condenser mic with selectable directionality, so you can change between cardioid and hypercardioid. If you can afford three mics, consider a hand-held dynamic, a shotgun condenser, and a lapel mic.

Comparisons

In the end, sound is quite subjective. You really want a mic which will provide the sound you like. A good idea is to set up a contolled test. Record the same sounds using different mics, keeping all other factors constant.

Make sure you are comparing apples with apples; for example, don't compare a hand-held cardioid and a shotgun in the same position. If you do want to compare these mics, make sure each is placed in its optimum position.

How to Position a Microphone

Distance

The golden rule of microphone placement is get the distance right. In general, place the microphone as close as practical to the sound source without getting so close that you introduce unwanted effects (see below).

The aim is to achieve a good balance between the subject sound and the ambient noise. In most cases you want the subject sound to be the clear focus, filled out with a moderate or low level of ambient noise. The desired balance will vary depending on the situation and the required effect. For example, interviews usually work best with very low ambient noise. However if you want to point out to your audience that the surroundings are very noisy you could hold the mic slightly further away from the subject.

It is possible to get too close. Some examples:

  • If a vocal mic is to close to the speaker's mouth, the audio may be unnaturally bassy (boomy, excessive low frequencies). You are also likely to experience popping and other unpleasant noises.
  • A microphone too close to a very loud sound source is likely to cause distortion.
  • Placing a mic too close to moving parts or other obstacles may be dangerous. For example, be careful when micing drums that the drummer isn't going to hit the mic.

Phase Problems

When using more than one microphone you need to be wary of phasing, or cancellation. Due to the way sound waves interfere with each other, problems can occur when the same sound source is picked up from different mics placed at slightly different distances. A common example is an interview situation in which two people each have a hand-held mic - when one person talks they are picked up by both mics and the resulting interference creates a phasing effect.

Think Laterally

You don't always have to conform to standard ways of doing things. As long as you're not placing a microphone in danger there's no reason not to use them in unusual positions. For example, lavalier mics can be very versatile due to their small size - they can be placed in positions which would be unrealistic for larger mics.

Examples

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Guitar amps are miced very closely. This helps keep the sound isolated from the rest of the stage noise. Theoretically the amp will not create any level burst strong enough to distort the microphone.

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Snare drum mics need to be close to the skin without getting in the way of the drummer or risking damage.

 


 

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