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Australian Linguistic Society4 December 2011
ANU, Canberra
David NathanEndangered Languages Archive
Hans Rausing Endangered Languages ProjectSOAS, University of London
Audio Theory and Practicefor Language Documentation
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Topics – audio and recording
Questions Epistemology Signal and noise Perception and psychacoustics Microphones Workflow Connections Implications for video Implications for metadata
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Questions
have you recorded audio? what else have you done with your audio?
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Question
are there any special audio-recording considerations for language documentation?
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Questions
you buy a recorder for $x. A matching microphone should cost:
(a) 3x (b) 0.75x(c) 0.3x (d) 0.1x (e) relative cost is irrelevant
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Question
Digitally recorded audio is better quality than analogue recorded audio because:
(a) digital microphones are more accurate (b) digital formats are more accurate (c) digital equipment is newer(d) digital formats capture more
information (e) no, digital audio is not better
than analogue audio
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Big questions
what are we actually recording? what is it for? what is the role of audio in language
documentation?
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Epistemology for audio in documentation
an audio recording is made in order to be experienced by a human listener
a recording conveys what a human listener would experience at a particular location in an event setting
documentation goals define recording methodology
a recording should capture spatial information metadata about the recording and the recording
setting are required for full interpretation ethical recording respects speakers and honours
their contribution through your effort and skill
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Evaluating recordings
accuracy: how well is the signal captured, as true to its sources and without distortion?
intelligibility/information accessibility: can the desired content be identified?
signal vs. noise: is the ratio acceptable? can the focal source be separated from all sources of noise?
listenability/comfort/aesthetics: is it easy on the ears? will it be debilitating to listen to for an extended time?
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Evaluating recordings
localisation of sources: is enough spatial information captured?
separation of noise: can all sources of noise be separated?
representation of environment: are the acoustic properties of the recording space appropriately represented?
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Evaluating recordings
content (identity, performance, uniqueness, coverage): were the right people recorded doing the right things?
editability/repurposeability: is the recording suitable for turning to relevant purposes?
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What is audio?
Audio is not data real world record acoustic phenomena represent (some) linguistic components derive data
Audio is a resource making it is both art and science a critical and ethical responsibility strongest relationship to communities it’s not necessary to record everything, but it is
neceessary to record well
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SIGNAL & NOISE
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Evaluating recordings
signal noise signal to noise ratio listenability (eg comfort, consistency) fit for purpose
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Evaluating recordings
audio professionals use their human ears as evaluator of audio quality and value, while many linguists (mistakenly?) look to formats, spectrographs, wave-forms, analyses etc
44.1 KHz, 24 bit
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Signal - what you want
content contextual and spatial information
Soundscape and ethnography
fidelity comfortable to listen to
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Noise - what you don’t want
from environment: near: people, animals, activities far: traffic, generators, planes machines: refrigerators, fans, computers not hearable: mobile phones, electrical
interference acoustic: reflections/resonance
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Noise - what you don’t want
generated by (unwanted parts of) event shuffling papers, clothes table banging backchannel from interviewer equipment handling, especially
microphones and cables (and recorders with built-in mics)
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Avoiding handling noise
use stands and cradles etc
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Noise - what you don’t want
generated by equipment wrong input levels circuity noise (cheap or incompatible) compression loss or distortion ALC/AGC effects (pumping) video camera motors
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Evaluating environment/situation
external environment access electricity external noise sources
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External noise sources
example possibilities for dealing with it
traffic investigate, record in quiet time
face away
use damping materials
children get them involved
show something to satisfy curiosity
animals choose time of day
weather (wind, thunder, rain etc)
use dead cat; wait; reschedule
see also General principles
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Dead cat
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Close-up noise sources
machinesexample possibilities for dealing with it
refrigerator pre-survey what comes on intermittently
turn off
relocate
motors, switching monitor
fans monitor, dead cat (windshield)
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Dealing with noise sources
be prepared and aware seek collaboration monitor use or modify room acoustics
location direction surfaces reflection absorption isolation
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Utilising room acoustics
location away from doors, windows, traffic areas
direction face away from noise sources
reflection avoid parallel surfaces
surfaces avoid hard smooth surfaces choose or create soft or rough surfaces
isolation find an ‘’airtight’’ place
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When is a noise not a noise?
When it is part of the content, for some interpretation of the eventJohn Cage performance
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PERCEPTION & PSYCHOACOUSTICS
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Audio perception/psychoacoustics
a human listener has: location, orientation in a physical setting two ears - incredibly sensitive a brain/mind
the mind selects from various sources of sound and other sensory information, using long- and short-term memory
listening is actually a “hallucination”
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Psychoacoustics and recording
microphones don’t have a mind: they can't distinguish wanted from unwanted sound
microphones don’t have “edges” like camera lenses
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Psychoacoustics and recording
the recording process removes acoustic information
if you only care about transcription, then you are going to throw away over 99% of the acoustic information!
real worldrecord acoustic phenomenarepresent (some) linguistic componentsderive data
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Implications for recording
typical recording methods are unscientific! … so what should we do?
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Implications for recording
plan and manage recording goals equipment preparation environment and setup sources changes and actions settings
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Implications for recording
why is it important to record spatial information?
what other information (acoustic or non-acoustic) do we need?
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“Sound stage”
spatial information is an essential part of audio
we are amazingly attuned to it we should record in stereo
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“Sound stage”
... or in ORTF (binaural)
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MICROPHONES
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Microphones and audio quality
microphones are the greatest determinant of audio recording quality selection of appropriate microphone(s) for
the task placement and handling of the
microphone(s)
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Microphones in the digital era
microphones in the digital era recorder quality has increased but prices
decreased microphones have become comparatively
more expensive why? microphones are analogue devices!
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Microphone types
principle: dynamic vs condenser directionality: omni, cardoid, and shotgun spatiality: mono, stereo, binaural
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Microphone physical principles
dynamic generate signal from sound pressure more robust, less accurate used for musical and live performance
condenser more fragile, sensitive and accurate need power source - battery or phantom
power in general, use condenser microphones for
language documentation
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Omni
lavalier or tie-clip microphones are typically omni-directional
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Microphone directionality - omni
omni-directional
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Cardioid
many “standard” handheld microphones are cardioid units
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Microphone directionality - cardioid
cardioid
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Shotgun
shotguns are good for quiet sources, in some noisy environments, and for video work
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Microphone directionality - shotgun
shotgun/directional/hypercardioid
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Stereo microphones
spatial information is an essential part of audio
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Full “sound stage”: ORTF
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Simulating ORTF with 2 cardioids
17cm
110°
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Microphones - quality
generally, you get what you pay for each model has its own subjective colour decent microphones for language
documentation fieldwork cost from £120 to £300
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Reputable makers - include
AKG Audio Technica Beyerdynamic Røde Sennheiser Shure Sony
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Microphone placement
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Microphone usage principles
where should the microphone be? in general, about 20cm from the speaker’s
mouth
the inverse square law is your friend ...
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The inverse square law
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The inverse square law
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Using the inverse square law
if you have noise sources, maximise the signal to noise ratio by: placing the microphone as close as possible
to the signal source placing the microphone as far as possible
from the noise source
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AUDIO WORKFLOW
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Audio workflow
who/what/where /why/how do you want to record?
contact people
audio training
budget, research, and buy equipment
assemble, test, practise
Before you go
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Audio workflow
transport safely
check environment, situations, permissions
make test recordings
local training & collaboration
On site, before recording
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Audio workflow
record!
monitor!
collect metadata
(label) check quality
monitor
Sessions
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Audio workflow
(label) check quality
backup add information (metadata, metadocumentation, transcriptions, annotations, etc)
After sessions
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Audio workflow
… send samples to archive
add information (metadata, metadocumentation, transcriptions, annotations, etc)
... package and send to archive
Later
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CONNECTIONS
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Microphone connections
plugs cable types cables for stereo/mono, multiple wireless power sources for condenser microphones -
battery or phantom power
see http://www.hrelp.org/archive/advice/microphones.html
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Microphone connections
minijack/miniplug (fragile)
RCA/phono
1/4 inch (headphone)
XLR (Canon)
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XLR
professionals always use them electrical contact is independent of the
physical connection latching is independent of the electrical
contact
you can use XML-to-miniplug cables or converters for recorders with miniplug inputs
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IMPLICATIONS FOR VIDEO
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Implications for video
video captures spatial information – but so does audio
so these need to be co-ordinated match audio microphones and pattern to
video framing and events camera location is often not the correct
location for microphone get L & R channels correct!
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Implications for video
video formats for audio component may be compressed – how much does this matter?
should we record audio separately or not?
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IMPLICATIONS FOR METADATA
document the goals document the environment document the layout/setup
e.g. directional language use: diagrams, photos, oral and written
descriptions (e.g of relationships)
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End
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