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Saami Winter SchoolFeb 10

Bodø, Norway

David NathanEndangered Languages Archive

Hans Rausing Endangered Languages ProjectSOAS, University of London

Audio Recording Techniques & Equipment

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Topics - session 1

Questions Audio workflow Evaluating recordings Perception and psychacoustics Microphones Connections Recorders Carriers

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QUESTIONS

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Questions

You buy a recorder for $x. A matching microphone would cost:

(a) 3x (b) 0.75x(c) 0.3x (d) 0.1x (e) none of these - cost is

irrelevant

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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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What is audio?

Audio is not data real world record phenomena represent phenomena 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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AUDIO WORKFLOW

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Audio workflow

who/what/where /why/how do you want to record?

contact people

audio training

equipment & budget

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 (transcriptions, annotations, metadata etc)

After sessions

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Audio workflow

send samples to archive

add information (transcriptions, annotations, metadata etc)

... package and send to archive

Later

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EVALUATING RECORDINGS

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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 the human ear as evaluator of audio quality and value, while many linguists mistakenly look to formats, wave-forms, analyses etc

44.1 KHz, 24 bit

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Signal - what you want

content contextual and spatial information 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 event (unwanted) shuffling papers, clothes table banging backchannel from interviewer equipment handling, especially

microphones and cables

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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 (windjammer)

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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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Room acoustics

location away from doors, windows, traffic areas

direction face away from noise sources

surfaces avoid hard smooth surfaces

reflection avoid parallel surfaces

absorption choose or create soft or rough surfaces

isolation find an ‘’airtight’’ place

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PERCEPTION & PSYCHOACOUSTICS

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Audio perception/psychoacoustics

audio information is diverse a human listener has:

location and orientation in physical world two ears - which are incredibly sensitive a brain/mind

the mind merges and selects from various sources of audio information

listening is actually a “hallucination” so what should we record? typical recording methods are unscientific!

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Psychoacoustics and recording

microphones are not like camera lenses they don’t have “edges” don't distinguish wanted and unwanted

info the recording process removes some

information

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Implications for recording

you need to set goals, plan and manage recording goals equipment sources environment settings

example: recording spatial information why is this important?

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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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Microphone directionality - omni

omni

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Omni

lavalier or tie-clip microphones are typically omni-directional

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Microphone directionality - cardioid

cardioid

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Cardioid

many “standard” handheld microphones are cardioid units

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Microphone directionality - shotgun

directional/shotgun/hypercardioid

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Shotgun

shotguns are good for quiet sources, in some noisy environments, and for video work

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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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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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RECORDERS

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Recorders

types and their strengths/weaknesses/implications

quality parameters accuracy (frequency response,

distortion, s/n ratio) reliability features versatility power sources, battery type

and battery life

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Recorders

media types, costs, properties, implications connections formats

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Using recorders

settings – levels, formats, AGC/ALC a second recorder? do you have to do it yourself?

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CARRIERS

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So you’ve recorded something?

carrier types to label ... or not preservation track the content

you may need to digitise/redigitise/capture it

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General guidelines for success

microphone choice monitoring familiarity and skill with equipment power and batteries a range of equipment, not the “perfect item”! consistency principle

juxtapositions efficient field sessions and later processing

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END OF AUDIO BASICS!

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PART 2: AUDIO PROPERTIES

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AUDIO SIGNALS

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Audio is initially analogue

analogue means an infinitely variable property of the real physical world

digital means a sequence of measurements of real world properties, ie symbols

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Audio signal parameters

pitch kHz - human voice fundamental 100 (m) – 200 (f) Hz formants 800 Hz – 4+ kHz harmonics, other, up to 15 kHz

amplitude (power) dB a relative and logarithmic measure 0 dB is reference point; sound of mosquito

flying at 3m max human is about 140 dB (pain = 120) each 6 dB step perceived as

doubling/halving volume

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signal to noise ratio of wanted to unwanted sound data the bigger the number the better

Signal parameters

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DIGITAL AUDIO

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Digital audio

Analogue Digital (identify and measure points)

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0 20 40 60 80 100-100

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1000

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nominal time

ampl

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Digital audio

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Digital audio parameters

digital means measuring or “sampling” where and when is it done?

the properties of digital audio are: sampling rate(Hz) sample size (“resolution”, “bit depth”) mono or stereo for compressed data: bit rate (Kb/s)

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Digital audio parameters

what do these mean? 11KHz, 8 bit 44.1 KHz, 16 bit 48 KHz, 24 bit 192 KHz, 48 bit

these have implications for quality file size compatibility, usage ...

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Encoding

“codecs” file formats eg WAV, AIFF, AU, MP3, Ogg

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reasons types

open and proprietary formats (eg MP3 vs ATRAC)

lossy and non-lossy (most are lossy) repeated compression unpredictable

distinguish sound information content from its encoding and its carrier

Compression

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Digitising

where is it actually done? involves either

digitisation (capturing/ingesting) re-digitisation (capturing) copying (may involve transcoding, e.g.

ATRAC)

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Digitising

where was your audio digitised?

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Digitisation: results and quality

what does the result depend on? player and digitising devices settings levels cables, connections, environment

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Digitisation: results and quality

where can quality be lost? (as well as original recording issues) poor treatment of carriers unknown properties of carriers (eg unlabeled) choice of output port, settings (level, format

etc) choice of input port, settings etc quality of player and digitising devices connections/cables, interference from other

devices or mains supply

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End