RTV 332 Audio Analog vs digital recording l
- Slides: 42
RTV 332 Audio
Analog vs. digital recording l Analog l l l ‘analogous to the original waveform’ Amplitude / frequencies / magnetic recording Audio tape / video tape (amount of information) Writing speed (analog tape / video helical scan) Digital l l Representation of the waveform with 1 s and 0 s Sampling and quantizing Compression of data ‘perfect’ copy
Basic analog process l l l l Sound waves Microphone diaphragm (transducer) Magnetic recording (encoding) Noise Generations Playback (decoding) Speakers (transducer)
Basic digital process l l l l Sound waves Algorithm for encoding (PCM) Sampling (‘snapshots’) Quantizing Sampling rate Compression (MPEG variations) (lossy? ) Decoding Various codecs
Sampling rates l l Analog: amplitude is the level component and frequency is the time -- digital, quantizing is the level and sampling is the time component 32 k. Hz: original broadcast digital audio 44. 1 k. Hz: CDs ° 48 k. Hz: DAT and mini. DV 96 k. Hz or 192 k. Hz: Blu. Ray
Sampling rates l l 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 l l l The full range of human hearing is between 20 Hz and 20 k. Hz. The minimum sampling rate that satisfies the sampling theorem for this full bandwidth is 40 k. Hz. The 44. 1 k. Hz 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 l l l 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 k. Hz, 48 k. Hz Think of film at 24 fps – each still frame is a ‘sample’ (snapshot) of information in 1/24 of a second
Digital Recording l l 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 l Sound wave l l l Frequency / Measured in hertz Amplitude / Measured in decibels (db-spl) l l l Compression / rarefaction AM/FM, k. Hz / MHz (r. f. ) Attack/sustain (internal dynamics)/decay -sound envelope Acoustics / Psychoacoustics / binaural hearing Absorbed / Reflected Direct / Indirect (echo & reverberation)
Some issues with sound l l Equal loudness principle--depending on loudness we don’t hear low and high frequencies as well as we hear middle Masking--Hiding of some sounds by other sounds when each is a different frequency and they are presented together. Loud over soft / lowerpitched over higher Acoustical phase--the time relationship between two or more sound waves at a given point in their cycles Timbre--a sound’s unique tone quality or tone color
Production Room Sound Design l l l l Ergonomics – human element in designing room Sound Absorption and Reflection Diffusion--scattering of sound waves Diffraction--spreading or bending Resonance--vibration of an object at the same frequency as the original body’s frequency Lively or Dead Room Isolation
Sound Frequency Spectrum l Bass l l l Midrange l l l Low bass, 1 st & 2 nd octaves, 16 -64 Hz Upper bass, 3 rd& 4 th octaves, 64 -256 Hz 5 th, 6 th & 7 th octaves, 256 - 2, 048 Hz Upper midrange: 8 th octave, 2, 048 - 4, 096 Hz Treble l 9 th & 10 th octaves, 4, 096 - 16, 384 Hz
Mics -- Review Sound l Sound Frequency Spectrum l l l Bass, midrange, treble Frequency / Hertz Amplitude / decibels Acoustics Direct / indirect sound l Echo / reverberations
Microphone Directional Patterns Omnidirectional / nondirectional l Unidirectional / Directional/ cardioid l l l Super, hyper, ultra Bidirectional
Main polar patterns Omni / nondirectional l Bi-directional / figure 8 l Unidirectional / cardioid l
Cardioid range Cardioid l Supercardioid l Hypercardioid l Shotgun mic is hyperdirectional l Phase cancellation l
The omnidirectional microphone is equally sensitive in all directions 18
Use a supercardioid pickup pattern whenever you want extremely selective pickup, to avoid environmental noises, or for distance sources. 19
The directional (or cardioid) mic has a broad, heart-shaped pattern that is insensitive on its rear side 20
Professional Mic types l l 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 l Close vs. distant miking l l l 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 l l lavaliere headset handheld studio/boom mounted TV boom types / largest to smallest l l Perambulator boom, giraffes, fishpole PZM (boundary mic)
Audio is as important to television as the video image. Ø It gives images a convincing realism. Ø It helps the audience feel involved. Ø It helps you follow the story. 24
Successful audio is a blend of: Ø Appropriate techniques Ø Appropriate artistic choices Ø Both of these are a matter of technical knowledge combined with experience. 25
THE VARIETY OF ANGLES OF THE SET WALLS, THE CURTAINS, CARPET, FURNITURE, AND PEOPLE HELP DAMPEN THE LIVE SOUND – BUT NOT TOO MUCH 26
Acoustic panels were placed on the walls of this audio room to reduce the “liveness” of the room 27
Mono sound: Ø “Single-eared” monaural representation of sound in space Stereo sound: Ø Creates illusion of space and dimension Surround sound: Ø Provides sense of envelopment when mixed correctly 28
During the shooting of a dramatic program, the boom operator got the microphone as close as possible, while still being off camera, because open-air sound does not usually travel far 29
Shotgun mics are commonly mounted on field cameras, especially for news shooting 30
Ø Shotgun mics give the best quality long-distance pickup from the subject Ø Must be aimed accurately But, when attached with the camera: Ø Sometimes too far away from the subject for the best sound Ø Mic doesn’t zoom with the zoom lens, so the sound capture remains the same Ø Camera mic can’t follow somebody 31
The handheld mic is widely used for interviews and commentaries, and stage work. If the mic has a cardioid directional response, extraneous noise pickup is lower. If the mic is omnidirectional, it may need to be held closer to the subject to reduce atmosphere sounds 32
Different types of wind screens are used to protect a shotgun mic from wind noise Video Production Handbook Chapter 10 (5 th Edition) 33
A Mic Boom (or fishpole) is a regular method of mounting the shotgun mic, particularly in the field. It allows the operator to stand several feet away from the subject 34
Lavalier mics come in different shapes and sizes. Generally. A lavalier mic is clipped to a necktie, lapel or shirt. Sometimes a “dual redundancy” pair is used when a standby mic is desired 35
This lavalier clip is designed to hold two microphones, providing a backup in case one fails 36
The boundary (pzm) mic is a low-profile mic that can pick up accurate sounds from six or more feet away 37
There are many types of mic stands and mounts, from bottom-weighted telescopic stands to small versions with thin, flexible, or curved tubing intended for lavalier or miniature mics 38
Wireless (radio) belt pack and transmitter. A lavalier mic can be plugged into the transmitter 39
VU meters and bar graphs are used to monitor the audio signal 40
A large surround sound audio mixer for television productions Video Production Handbook Chapter 10 (5 th Edition) 41
Chapter 10 Audio for Video …parts of the console / mixing sound 42
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