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Audio theory and practice for language documentation. LingDy 12 Feb 2013 TUFS, Tokyo David Nathan Endangered Languages Archive Hans Rausing Endangered Languages Project SOAS, University of London. Questions. have you recorded audio? have you published audio?
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Audio theory and practicefor language documentation LingDy 12 Feb 2013 TUFS, Tokyo David Nathan Endangered Languages Archive Hans Rausing Endangered Languages Project SOAS, University of London
Questions • have you recorded audio? • have you published audio? • what else have you done with your audio?
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
Big questions • what are we actually recording? • what/who is it for? • what is the role of audio in 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
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 • see also General principles
Close-up noise sources • machines
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 event John Cage performance Available on iTunes (150 yen)
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 world • record acoustic phenomena • represent (some) linguistic components • derive 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 in ORTF (binaural)
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 • shotguns are good for quiet sources, in some noisy environments, and for video work
Microphone directionality - shotgun shotgun/directional/hypercardioid
Stereo microphones • spatial information is an essential part of audio
Full “sound stage”: ORTF • now the “best practice” for field recordings” (Austrian Academy of Science, Vienna Phonogrammarchiv) Superlux S502 Full binaural on dummy head
110° 17cm Simulating ORTF with 2 cardioids
Microphones - quality • generally, you get what you pay for • each model has its own subjective “colour” • good microphones for language documentation cost from $180 to $500
Reputable makers - examples • AKG • Audio Technica • Beyerdynamic • Røde • Sennheiser • Shure • Sony
Microphone usage principles • where should the microphone be? • in general, about 20cm from the speaker’s mouth • the inverse square law is your friend ...