Transcript Audio Recording And Production: An Introduction

Audio Recording And
Production: An Introduction
Soam Acharya
CS 731
Spring 1998
Contents
• sound basics
• acoustics/psycho-acoustics
• actual recording process
Characterizing Sound
•
•
•
•
•
Frequency and Pitch
Amplitude and Loudness
Frequency and Loudness
Acoustic Phase
Timbre
Frequency And Pitch
• 20 - 16000 Hz
– “feel” outside this range
• low bass:
20 - 80 Hz
– traffic, thunder, explosions
• upper bass:
80 - 320 Hz
– fullness/boomy
– rhythm instruments: drums, bass, low piano
• midrange:
320 - 2560 Hz
– fundamental of most sound sources
– intensity
• upper midrange:
2560 - 5120 Hz
– highest sensitivity
• treble:
– brilliance/sparkle
5120 - 20000 Hz
Amplitude and Loudness
• db-SPL = 20 * log10 (sound pressure/ref. sound pressure)
• can hear loudness at 1 - 10000000 or greater
• the db type measurement also used frequently
elsewhere
Amplitude and Loudness II
dBSPL
140
Airport runway, inside a bass drum
120
Threshold of pain: thunder, “in your face” vocals
100
subway
80
1” away from acoustic guitar
60
Average conversation
40
Subdued conversation
20
0
Furnished living room
Threshold of hearing
Frequency and Loudness
[p23 - fig 2-7]
(in)equal loudness principle
masking
equalization
Timbre
Tone quality or color
Timbre II
Shape of sound or envelope
Acoustics/Psycho-acoustics
• direct waves
• early reflection
• later reflection (reverberation)
– body
– decay or reverberation time
• echo
– long reflection path
Sound In An Enclosed Room
P35 - 3-2
Reverberation Vs. Decay Time
Decay
Time
Conference room
living room w. rugs
Inside a car
closet
Concert hall
gymnasium
Tiled bathroom
Open field
Reverberation
Surface Shape of Room
Parallel:
standing waves
Concave:
concentrate
Concave:
disperse
Studio Room Surface
P42 - 3-10
Studio Room Materials
• Sound absorption coefficient
– 0 reflects, 1 absorbs
– drapes > glass
• porous absorbers
– acoustical tiles, carpets, fibreglass, urethane
foams
• bass taps (diaphragmatic absorbers)
– wood panels mounted over air space
Actual Recording Process
Sound to
electric signal
Analog processing/mixing
Computer
storage
digital to analog
playback
analog to digital
Processing/editing
Converting Sound to Electricity: Microphones
• moving coil
– diaphragm, magnet, coil in a magnetic field
– robust, not sensitive to transients, less expensive
• ribbon microphone
– metal ribbon in a magnetic field
• printed ribbon
– more robust design
– good high frequency response
– low output level ie. not sensitive
Capacitor/Condenser Microphone
spacer
Back plate
Air film
Diaphragm front plate
• Needs separate power supply for pre-amp
– electret type: pre-charged, can get away with batteries
• professional use
• high sensitivity, output level (large SNR)
Microphone Pickup Patterns
• Omnidirectional
– all over
– non directional
• Bidirectional
– front and rear
• Unidirectional
– front only
– cardioid
– unidirectional
Pickup Patterns II
Pickup Patterns III
P 76 - 5-10
Reading A Microphone Spec.
Cardioid
polar response diagram
Reading a Microphone Spec II
Frequency response plot
Proximity Effect of Mic.
Relative
level (dB)
1/4” from mic
2” from mic
frequency
Microphone Accessories I
windscreen
Pop-screen
Microphone Accessories II
XLR -male
XLR-female
1/4”
RCA
3.5 “
(miniplug)
Specialty Microphones
•
•
•
•
lavalier
shotgun
parabolic
wireless
Lavalier Microphones
• To be worn on lapels
• omnidirectional
• built-in high freq. boost (chin cutoff)
Wireless Microphones
• FM transmitter
• UHF/VHF FCC approved
• multiple modes
Shotgun Microphones
• Long distance pickup
– need for unobtrusiveness on sets
• attenuate sound from all angles except a
narrow one in the front
• supercardioid/hypercardioid/ultracardioid
• less directional at lower freq.s
Parabolic Microphones
• Also long-distance pickup
• omni/uni directional microphone
Deploying Microphones
•
•
•
•
•
•
Acoustic/electrical phases
omnidirectional vs. unidirectional
miking speech for radio
miking speech for tv
recording music
reducing unwanted sounds
Acoustic/Electrical Phases
• Acoustic phases cancellation
– 3:1 rule for microphones
• dist between two microphones >= dist between
source and main microphone
P 292 12-1
Omni vs. Uni directional
• Omni
–
–
–
–
does not have to be held directly in front
picks up more ambience
less susceptible to wind, popping
more resilient to distance
• Uni
– cuts down unwanted sound
– no sense of environment
– reduces feedback in reverberant locations
Miking Speech in Radio
• Stay within pickup pattern
• mic-to-source distance
– inverse square law
– proximity
• weak voice
• lip smacking
• diffusion of sound quality
Miking Speech in Radio II
• Across directional mic face
• reduces freq. response
P 297 12-5
• 45 deg. angle
P297 - 12-6
Stereo Miking
• Two microphones
– difference in arrival time between microphones
• phase problems when combining to mono
• Coincident miking
– two directional microphones together on same
vertical axis
– minimize disparity in arrival times
Stereo Miking II
P 304, 12-13
Miking for TV
• News and interviews
• Panel and talk programs
• miking the audience
News and Interviews
– Omnidirectional lavalier
• hide under clothes
– rustling/movment
– inhibits higher frequencies
Panel and Talk Programs
• Host/guest:
– Lavalier microphones
• unobtrusive
• easy to mount
• mic-source constant
• Mobile host
– handheld
• pop filter/ shock mount
• host can control source distance
• go to audience
Miking Audience
• Directional shotgun microphones
– distribute them in equal quadrants above the
audience
• audience monitor loudspeaker feedback
– offaxis to microphones
Recording Music
• Distant miking
– ensemble, reduces electronic noise
– air loss with distance: freq dependent
– phase
• close miking
– control
– better separation of sources
Recording Music II
• Miking instruments
– drums
• bass drum: coil
• damping
• hi-hat: capacitor
– violin/viola
• multiple microphones to capture the range
– vocals
• proximity effect
• sibilance
• compression
Putting It Together
P 409 - 14-67
Reducing Noise
• Microphone location
– near noisy sources
• outdoor location:
– noise suppressors (eq dialogue)
• shielding
• noise gates
Roadmap
Sound to
electric signal
Analog processing/mixing
Computer
storage
digital to analog
analog to digital
Processing/editing
Analog Processing/Mixing
Analog Processing/Mixing II
• Input:
–
–
–
–
–
–
–
–
–
–
overload indicator
trim
phantom power
equalizer/filter
phase reversal
panning
bus assignment (input signals to output buses)
cuing (for auditioning)
meters
mute
Analog Processing/Mixing III
• Output:
–
–
–
–
buses (to group signals)
bus fader
effects modules
output meter
Patch Panel
P141 - 6-11, 6-12
Roadmap
Sound to
electric signal
Analog processing/mixing
Computer
storage
digital to analog
analog to digital
Processing/editing
Soundcards
A/D
D/A
input
Low pass
sampling
D/A
Low pass
output
Soundcard Problems
• Poor quality: 80dB SNR as opposed to >90
dB SNR value for CD players
• background hissing noise
– mute unwanted sources into soundcard
• humming noise when connected to hifi
– ground loop
• hissing from microphones
– noisy mic preamps
Soundcard Problems II
• Distortion during playback
– clipping in the mixer chip
Roadmap
Sound to
electric signal
Analog processing/mixing
Computer
storage
digital to analog
analog to digital
Processing/editing
Processing
• spectrum signal processors
– equalizers, filters
• time signal processors
– reverb, delay
• amplitude processors
– compressors/limiters, expanders/noise gates
Spectrum Signal Processor
• Equalization
gain
High frequency
Max boost.
frequency
Max cut.
Turnover freq.
stop freq.
Spectrum Signal Processor II
Graphic equalizer: fixed frequency
Parametric: variable frequency
Spectrum Signal Processors III
• Filters:
–
–
–
–
high pass
low pass
bandpass
notch
Time Signal Processors
• Reverb
• Delay
– doubling
– chorus
– slap back
Time Signal Processors II
• Flanging
– double sound source, delay one, mix
sound
delay
Time Signal Processors III
• Phasing
– double sound source, phase shift one, mix
sound
Phase
shift
Time Signal Processors IV
• Pitch shift
– time compression
Amplitude Processors
Compressors and limiters
P 234, 9-25
Amplitude Processors II
Noise gates
P 238, 9-28
Editing: Cubase VST
The Transport Bar
Editing II
Arrangement
Window
Editing III
The Parts Display
Editing IV
The Audio Mixer Window
EQ and
Effect Windows
The Audio Pool
Audio
editor
Wave
editor
Midi Editing