DocLing2016
David Nathan & Anthony Jukes
Audio theory and practicefor language documentation
An 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
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 comfortable to listen to for an extended time?
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?
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?
Recording audio 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 necessary
to record well
SIGNAL & NOISE
Evaluating recordings signal noise signal to noise ratio listenability (eg comfort, consistency) fit for purpose
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
Signal - what you want content contextual and spatial information fidelity comfortable to listen to
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
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)
Avoiding handling noise use stands and cradles etc
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
External noise sources
example possibilities for dealing with it
traffic investigate, record in quiet timeface awayuse damping materials
children get them involvedshow something to satisfy curiosity
animals choose time of day
weather (wind, thunder, rain etc)
use dead cat; wait; reschedule
Dead cat
Close-up noise sources machines
example possibilities for dealing with itrefrigerator pre-survey what comes on intermittently
turn offrelocate
motors, switching monitor
fans monitor, dead cat (windshield)
Dealing with noise sources be prepared and aware seek collaboration monitor use or modify room acoustics
location direction surfaces reflection absorption isolation
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
When is a noise not a noise? When it is part of the content, for some interpretation of
the eventPerformance of John Cage 4”33’Available on iTunes (150 yen)
PERCEPTION & PSYCHOACOUSTICS
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”
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
Psychoacoustics and recording the recording process loses acoustic
information if you only care about transcription, then you
are going to throw away over 99% of the acoustic information anyway!
real worldrecord acoustic phenomenarepresent (some) linguistic componentsderive data
Implications for recording typical recording methods are unscientific! … so what should we do?
Implications for recording plan and manage recording
goals equipment preparation and settings other preparation environment and setup sources changes, actions, settings
Implications for recording why is it important to record spatial information? what other information (acoustic or non-acoustic) do we
need?
“Sound stage” spatial information is an essential part of
audio we are amazingly attuned to it we should record in stereo
“Sound stage” ... or ORTF (binaural)
MICROPHONES
Microphones and audio quality microphones are the greatest factor in audio recording
quality selection of appropriate microphone(s) for the task placement and handling
Microphone types principle: dynamic vs condenser directionality: omni, cardoid, and shotgun spatiality: mono, stereo, ORTF, binaural
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
Omni lavalier or tie-clip microphones are typically omni-
directional
Microphone directionality - omni
omni-directional
Cardioid many “standard” handheld microphones are cardioid
units
Microphone directionality - cardioid
cardioid
Shotgun (= directional, hypercardioid) shotguns are good for
quiet sources in some noisy environments video work
Microphone directionality - shotgun
shotgun/directional/hypercardioid
Head-mounted microphones head-mounted microphones are excellent for very noisy
environments or mobile activties, and may be omni-directional or cardioid
Stereo microphones spatial information is an important part of audio
Full “sound stage”: ORTF
Superlux S502
Full binaural on dummy head
ORTF & Binaural
ORTF is now the “best practice” for field recordings” (Austrian Academy of Science, Vienna Phonogrammarchiv)
Simulating ORTF with 2 cardioids
17cm
110°
Microphones - quality generally, you get what you pay for each model has its own subjective “colour” good microphones for language documentation cost
from US$180 to US$500
Reputable makers - examples AKG Audio Technica Beyerdynamic Røde Sennheiser Shure Sony
Microphone placement
Microphone usage principles where should the microphone be? in general, about 20cm from the speaker’s mouth
the inverse square law is your friend ...
The inverse square law
Using the inverse square law if you have noise sources, increase 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
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
Microphone connections
1/8 inch “mini-jack”
RCA/ “phono plug”
1/4 inch “jack plug”
XLR “Canon”
XLR the physical connection is independent of the
electrical connection transmits phantom power low-noise over long cable runs you can use XML to mini-jack cables or
converters for recorders with mini-jack inputs
Choice of Recorders
Connectors - XLR or mini-jack or both?
Ruggedness and build Accuracy Media type Battery life Cost
AUDIO WORKFLOW
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
Audio workflow
transport safely
check environment, situations, permissions
make test recordings
local training & collaboration
On site, before recording
Audio workflow
record!monitor!
collect metadata
check quality
monitor
Sessions
select equipment(microphones)
Audio workflow
(label) check quality
backup add information (metadata, metadocumentation, transcriptions, annotations, etc)
After sessions
Audio workflow
add information (metadata, metadocumentation, transcriptions, annotations, etc)
package and send to archive
Later
other audio outcomes and resources
End !