RTV 332Audio

Analog vs. digital recording

Analog ‘analogous to the original waveform’ Amplitude / frequencies / magnetic recording Audio tape / video tape (amount of information) Writing speed (analog tape / video helical scan)

Digital Representation of the waveform with 1s and 0s Sampling and quantizing Compression of data ‘perfect’ copy

Basic analog process

Sound waves Microphone diaphragm (transducer) Magnetic recording (encoding) Noise Generations Playback (decoding) Speakers (transducer)

Basic digital process

Sound waves Algorithm for encoding (PCM) Sampling (‘snapshots’) Quantizing Sampling rate Compression (MPEG variations) (lossy?) Decoding Various codecs

Sampling rates

Analog: amplitude is the level component and frequency is the time -- digital, quantizing is the level and sampling is the time component

32 kHz: original broadcast digital audio 44.1 kHz: CDs ° 48 kHz: DAT and miniDV 96 kHz or 192 kHz: BluRay

Sampling rates

The Nyquist–Shannon sampling theorem: perfect reconstruction of a signal is possible when the sampling frequency is greater than twice the maximum frequency of the signal being sampled,

For example, if a signal has an upper band limit of 100 Hz, a sampling frequency greater than 200 Hz will avoid aliasing and would theoretically allow perfect reconstruction.

Sampling rates The full range of human hearing is between

20 Hz and 20 kHz. The minimum sampling rate that satisfies the

sampling theorem for this full bandwidth is 40 kHz. The 44.1 kHz sampling rate used for Compact Disc was chosen for this and other technical reasons.

Aliasing: the distortion or artifact that results when the signal reconstructed from samples is different from the original continuous signal.

Digital Recording

Sampling: takes periodic samples (snapshots, voltages) of the analog signal and converts that information into digital data

Sampling frequency: the rate at which the signal is sampled: 44.1 kHz, 48 kHz

Think of film at 24 fps – each still frame is a ‘sample’ (snapshot) of information in 1/24 of a second

Digital Recording Quantization: how many ones and zeroes to

represent each sample A quantity expressed as a binary number is

called a digital word. 10 is a 2-bit word, 101 is a 3-bit, 1010 is a 4-

bit etc. The greater the number of the quantizing

level (10010110 an 8 bit vs. 10, a 2 bit) the more accurate the representation of the analog signal.

Sound in an environment Sound wave

Compression / rarefaction Frequency / Measured in hertz Amplitude / Measured in decibels (db-spl)

AM/FM, kHz / MHz (r.f.) Attack/sustain (internal dynamics)/decay --

sound envelope Acoustics / Psychoacoustics / binaural hearing Absorbed / Reflected Direct / Indirect (echo & reverberation)

Sound Frequency Spectrum

Bass Low bass, 1st & 2nd octaves, 16-64 Hz Upper bass, 3rd& 4th octaves, 64-256 Hz

Midrange 5th, 6th & 7th octaves, 256 - 2,048 Hz Upper midrange: 8th octave, 2,048 - 4,096 Hz

Treble 9th & 10th octaves, 4,096 - 16,384 Hz

Mics -- Review Sound

Sound Frequency Spectrum Bass, midrange, treble

Frequency / Hertz Amplitude / decibels Acoustics Direct / indirect sound

Echo / reverberations

Microphone Directional Patterns

Omnidirectional / nondirectionalUnidirectional / Directional/ cardioid

Super, hyper, ultraBidirectional

Main polar patterns

Omni / nondirectional

Bi-directional / figure 8

Unidirectional / directional / cardioid

Cardioid rangeCardioidSupercardioidHypercardioidShotgun mic is

hyperdirectionalPhase

cancellation

The omnidirectional microphone is equally The omnidirectional microphone is equally sensitive in all directionssensitive in all directions

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Use a supercardioid pickup pattern whenever you want Use a supercardioid pickup pattern whenever you want extremely selective pickup, to avoid environmental extremely selective pickup, to avoid environmental

noises, or for distance sources.noises, or for distance sources.

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The directional (or cardioid) mic has a broad, heart-shaped The directional (or cardioid) mic has a broad, heart-shaped pattern that is insensitive on its rear sidepattern that is insensitive on its rear side

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Professional Mic types

Moving coil/dynamic Ribbon Capacitor/condensor Transducer – changes energy from one form

to another – in this case sound waves into an electrical current

More about mics and sound

Close vs. distant miking Cross-pair, mid-side as some distant miking

approaches Close mic speakers on camera / filmmaking wide

shots must do ADR Wide response – range of frequencies the mic

will pick up Flat response – accurately recreates

frequencies Colored response – changes frequencies

(lavaliere boosts high frequencies, for example

Common mic types

lavaliere headset handheld studio/boom mounted TV boom types / largest to smallest

Perambulator boom, giraffes, fishpole PZM (boundary mic)

Audio is as important to television as Audio is as important to television as the video image. the video image.

It gives images a convincing realism. It gives images a convincing realism.

It helps the audience feel involved. It helps the audience feel involved.

It helps you follow the story. It helps you follow the story.

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Successful audio is a blend of:Successful audio is a blend of:

Appropriate Appropriate techniquestechniques

Appropriate Appropriate artistic choicesartistic choices

Both of these are a matter of technical knowledge combined with experienceBoth of these are a matter of technical knowledge combined with experience..

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THE VARIETY OF ANGLES OF THE SET WALLS, THE CURTAINS, THE VARIETY OF ANGLES OF THE SET WALLS, THE CURTAINS, CARPET, FURNITURE, AND PEOPLE HELP DAMPEN THE LIVE CARPET, FURNITURE, AND PEOPLE HELP DAMPEN THE LIVE

SOUND – BUT NOT TOO MUCHSOUND – BUT NOT TOO MUCH

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Acoustic panels were placed on the walls of this Acoustic panels were placed on the walls of this audio room to reduce the “liveness” of the roomaudio room to reduce the “liveness” of the room

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Mono sound:Mono sound: ““Single-eared” monaural representation of sound in spaceSingle-eared” monaural representation of sound in space

Stereo sound:Stereo sound: Creates illusion of space and dimensionCreates illusion of space and dimension

Surround sound:Surround sound: Provides sense of envelopment when mixed correctlyProvides sense of envelopment when mixed correctly

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During the shooting of a dramatic program, the boom During the shooting of a dramatic program, the boom operator gets the microphone as close as possible, while operator gets the microphone as close as possible, while still being off camera, because open-air sound does not still being off camera, because open-air sound does not

usually travel farusually travel far27

Shotgun mics are commonly mounted on field Shotgun mics are commonly mounted on field cameras, especially for news shooting (nat)cameras, especially for news shooting (nat)

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Shotgun mics give the best quality long-distance pickup from the subjectShotgun mics give the best quality long-distance pickup from the subject

Must be aimed accuratelyMust be aimed accurately

But, when attached with the camera:But, when attached with the camera: Sometimes too far away from the subject for the best soundSometimes too far away from the subject for the best sound

Mic doesn’t zoom with the zoom lens, so the sound capture remains the same --- ‘presence’ issue Mic doesn’t zoom with the zoom lens, so the sound capture remains the same --- ‘presence’ issue

Camera mic can’t follow somebodyCamera mic can’t follow somebody

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The handheld mic is widely used for interviews and The handheld mic is widely used for interviews and commentaries, and stage work. If the mic has a cardioid commentaries, and stage work. If the mic has a cardioid directional response, extraneous noise pickup is lower. If directional response, extraneous noise pickup is lower. If the mic is omnidirectional, it may need to be held closer the mic is omnidirectional, it may need to be held closer

to the subject to reduce atmosphere soundsto the subject to reduce atmosphere sounds

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Different types of wind screens are used to protect Different types of wind screens are used to protect a shotgun mic from wind noisea shotgun mic from wind noise

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A Mic Boom (or fishpole) is a regular method of mounting A Mic Boom (or fishpole) is a regular method of mounting the shotgun mic, particularly in the field. It allows the the shotgun mic, particularly in the field. It allows the operator to stand several feet away from the subjectoperator to stand several feet away from the subject

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Lavalier mics come in different shapes and sizes. Lavalier mics come in different shapes and sizes. Generally. A lavalier mic is clipped to a necktie, Generally. A lavalier mic is clipped to a necktie, lapel or shirt. Sometimes a “dual redundancy” lapel or shirt. Sometimes a “dual redundancy”

pair is used when a standby mic is desiredpair is used when a standby mic is desired

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This lavalier clip is designed to hold two microphones, This lavalier clip is designed to hold two microphones, providing a backup in case one failsproviding a backup in case one fails

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The boundary (pzm) mic is a low-profile mic that can The boundary (pzm) mic is a low-profile mic that can pick up accurate sounds from six or more feet awaypick up accurate sounds from six or more feet away

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There are many types of mic stands and mounts, There are many types of mic stands and mounts, from bottom-weighted telescopic stands to small from bottom-weighted telescopic stands to small

versions with thin, flexible, or curved tubing versions with thin, flexible, or curved tubing intended for lavalier or miniature micsintended for lavalier or miniature mics

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Wireless (radio) belt pack and transmitter. A Wireless (radio) belt pack and transmitter. A lavalier mic or a handheld mic can be plugged lavalier mic or a handheld mic can be plugged into the transmitter (XLR or other connector)into the transmitter (XLR or other connector)

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VU meters and bar graphs are used to VU meters and bar graphs are used to monitor the audio signalmonitor the audio signal

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A large surround sound audio mixer for television A large surround sound audio mixer for television productions – faders, EQ, pan pots, trim, assignproductions – faders, EQ, pan pots, trim, assign

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…parts of the console / mixing sound, as time

permits

…mixing vs. layering sound

…audio console vs. DAW

Chapter 10

Audio for Video