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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
Schaefermeyer Digital Video BASICS 3
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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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Schaefermeyer Digital Video BASICS 44
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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Schaefermeyer Digital Video BASICS 55
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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Schaefermeyer Digital Video BASICS 66
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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Schaefermeyer Digital Video BASICS 77
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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Schaefermeyer Digital Video BASICS 88
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.
Schaefermeyer Digital Video BASICS 9
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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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Schaefermeyer Digital Video BASICS 1010
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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Schaefermeyer Digital Video BASICS 1111
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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Schaefermeyer Digital Video BASICS 1212
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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Schaefermeyer Digital Video BASICS 1313
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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Schaefermeyer Digital Video BASICS 1414
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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Schaefermeyer Digital Video BASICS 1515
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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Schaefermeyer Digital Video BASICS 1616
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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Schaefermeyer Digital Video BASICS 1717
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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Schaefermeyer Digital Video BASICS 1818
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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Schaefermeyer Digital Video BASICS 1919
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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Schaefermeyer Digital Video BASICS 2020
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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Schaefermeyer Digital Video BASICS 2121
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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Schaefermeyer Digital Video BASICS 2222
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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Schaefermeyer Digital Video BASICS 2323
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.