RTV 332 Audio
Dec 30, 2015
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 got the microphone as close as possible, while operator got 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 shootingcameras, especially for news shooting
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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 Mic doesn’t zoom with the zoom lens, so the sound capture remains the same
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
31Video Production Handbook Chapter 10 (5th Edition)
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 can be plugged into the transmitterlavalier mic can be plugged into the transmitter
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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 productionsproductions
39Video Production Handbook Chapter 10 (5th Edition)
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…parts of the console / mixing sound
Chapter 10
Audio for Video