Unit 2 Lesson 07

1

Lesson 7Production Audio

Digital Video BASICS

Schaefermeyer

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Schaefermeyer Digital Video BASICS 22

Objectives

Describe how sound is created and travels Tell how digital audio is created Explain how microphones work List the different types of microphones Describe microphone pick up patterns


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Objectives (continued)

Explain the different ways microphones are used

List the different audio connectors Describe wireless systems List other audio equipment Identify the keys to acquiring good audio

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Vocabulary

Amplitude Balanced audio Bidirectional

microphone Bit depth Boom microphone Cardioid microphone

Condenser microphone Dynamic microphone Field mixer Frequency Hypercardioid

microphone

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Vocabulary (continued)

Lavalier microphone

Omnidirectional microphone

Mini connector Pick up pattern RCA connector Ribbon microphone

Sample rate Supercardioid

microphone Telephone or TRS

connector Wavelength XLR connector

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Introduction

Even the best video images in the world quickly can be undone by bad audio.

We seem to be more forgiving of bad video than we are of bad audio.

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How Sound is Created and How Sound Travels

Vibrating objects create sound waves that travel through the air.

Your eardrums vibrate when the sound wave reaches your ear and is transferred to your brain.

A sound wave has three important properties:– Wavelength: Distance between equivalent points on

consecutive phases of a wave pattern– Frequency: Number of times a wavelength repeats in one

second– Amplitude: Power of the wave (also called volume)

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How Digital Audio is Created

Digital audio copies the analog signal by sampling—picking points along the analog wave each second and assigning them a numerical value that a computer can work with.


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How Digital Audio is Created (continued)

Two factors determine audio quality:– Sample rate: Number of times in a second that a

sample is chosen from the analog signal– Bit depth: Number of levels (or how high and how

low) a sample can recreate

Basic principle of sample rate

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How Microphones Work

To record only the audio you really want to use, place the microphone as close to the subject as possible.

All microphones work in the same basic way—each has an object or device that vibrates when audio waves reach it and a method for translating those vibrations into an electronic signal. The electronic signal is then moved through a wire and stored on some type of recording media.

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Different Types of MicrophonesDynamic Microphone

A dynamic microphone contains a diaphragm that vibrates with the audio waves.– Advantages—Rugged, do not require a power

source, are not as expensive as some other types of microphones, are not as sensitive to extra movement and handling

– Disadvantage—Does not pick up as wide of a range of frequencies as other microphones

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Different Types of MicrophonesCondenser Microphone

A condenser microphone uses two metallic diaphragms mounted very closely to a back plate.– Advantage—More sensitive to a wider range of

frequencies, which means a more faithful reproduction of the original signal

– Disadvantages—Requires a power source, not as rugged as dynamic microphones

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Different Types of MicrophonesRibbon Microphone

In a ribbon microphone, a metal corrugated ribbon is placed between the opposite poles of a magnet.– Advantage—High quality sound reproduction– Disadvantage—Fragile; breathing too hard on a

ribbon microphone can damage it

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Describe Microphone Pickup Patterns

A pickup pattern determines the area around the microphone where the microphone is sensitive to sounds.

An omnidirectional microphone is sensitive to sounds that come from all around the microphone.

A cardioid microphone picks up sounds in a heart-shape pattern.

Pick-up pattern of a cardioid microphone

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Describe Microphone Pickup Patterns (continued)

A supercardioid microphone has a narrower pickup pattern in the front than a cardioid and picks up some sound from behind.

A hypercardioid microphone has an even narrower pickup pattern in the front than the supercardioidand a little more in the rear.

Bidirectional microphones pick up audio in the front and in the rear, but not from the sides.

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The Different Ways Microphones Are Used

Camera-mounted microphone: Good for picking up ambient, or background, sound

Hand held mics: Can be positioned wherever needed and are seen by the audience

Boom microphones: Connected to a boom pole to get as close to the subject as possible without being seen by the audience

Lavalier microphones: Small mics that can be attached directly to the subject’s clothes

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The Different Ways Microphones Are UsedWired Systems and Different Audio Connectors

Wired microphones are more reliable and create higher quality audio than wireless.

A wired microphone has wires that connect the microphone to your recording device.

Unbalanced audio cable and connectors (like RCA and Mini) use two lines to transmit the signal and are susceptible to equipment noise.

Balanced audio lines and connectors (like XLR and TRS) use a third cable to provide a clearer signal that can move over greater distances.

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Wireless Systems

Wireless microphones differ in the way they transfer the audio signal to the recording device.

A microphone is connected to a wireless transmitter that can be attached to the subject and a receiver is then connected to the camera or recording device.

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Other Audio Equipment

A good pair of headphones allows you to hear what you are recording and check the audio levels.

A field mixer is a portable audio mixer that runs on batteries so you can adjust the microphone audio levels.

A small back-up recorder helps ensure you have the audio you need.

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Keys to Acquiring Good Audio

Getting good audio has more to do with people than with equipment.

Scout the location with audio in mind, at the same time as when you will shoot.

Close your eyes and focus on listening to get a better idea of what is likely to happen while you are shooting.

Try to have at least one person concentrating on audio.

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Summary

Sound is created by vibrating objects. The vibrations disturb the air molecules around the object, which in turn disturbs the air molecules next to them. This creates an audio wave that travels through the air.

The wave attributes that are important to understand are wavelength, frequency, and amplitude.

Frequency is measured in hertz (Hz), while amplitude is measured in decibels (dB).

Digital audio is created by sampling, much the same way as digital video is created from analog video. Bit depth determines how close each sample can get to the original signal. DV audio is 16 bit 44.1 kHz.

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Summary (continued)

All microphones work in the same basic way. First, an element, usually a diaphragm, vibrates with the audio waves. The vibrations create an electrical current that is sent to some type of a storage device.

The three most common types of microphones are dynamic, condenser, and ribbon.

Each microphone has an area around it that is sensitive to sound called a pickup pattern.

Microphones can be camera mounted, handheld, boom, or lavalier.

The four commonly used audio connectors are RCA, mini, XLR, and telephone. RCA and mini are unbalanced, while XLR and telephone connectors are balanced.

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Summary (continued)

Balanced audio uses a third wire that helps eliminate noise and hum.

Wireless systems consist of a transmitter connected to the microphone and a receiver connected to the camera.

Headphones, field mixers, and portable recorders are other pieces of equipment you might want to have.

People are the key to acquiring good audio. Scouting locations at the same time that a shoot is scheduled, listening while your eyes are closed, and having somebody focusing solely on audio helps make sure that the audio is as good as possible.