Recording sound: people, environment and equipment

Tom Castle David NathanRob Kennedy

Outline

1. Situations2. Psychoacoustics

and sound stage3. Microphones4. Recorders5. Methods and

principles6. Audio signals7. Today’s practical

8. Defining digital audio9. Compression10.Carriers11.Digitisation12.Editing and converting13.Principles

1. Situations

Situations

(External) environment access electricity external noise sources

... Environment (ext)

external noise sources (cont’d)example possibilities for dealing with it

traffic investigate, record in quiet timeface awayuse damping materialssee also General principles

kids get them involvedshow something to satisfy curiosity

animals choose time of daysee also General principles

weather (thunder, rain etc) try to minimise problems

Environment (close-up)

Internal environment Machines

example possibilities for dealing with it

Refrigerator Survey what comes on intermittentlyTurn offAvoid!

Motors, switching Avoid electrical interference

Fans Unexpected noise introduced

... Environment (close-up)

Yourself! overlap, shuffling papers, mic handling, table thumping

Other people Mobile phones (calling and polling) Room acoustics (and what to do about it)

reflection vs absorption isolation

2. Psychoacoustics and sound stage

Psychoacoustics

The microphone is not like the lens!And doesn't have a brain attached!Will pick up in all directions

Can't distinguish wanted and unwantedVision for your earsYour brain recognises and rejects soundsRecording process removes many cuesTherefore need to optimise recording process

at point of capturing sound waves

“Sound stage”

Listening as a “hallucination”Purpose of audio - for a human listener, who

has:earsbrain spatial location

Our normal approach to recording is unscientific; reduces events to data

What is “fidelity”?

“Sound stage”

Spatial information is an essential part of audio We are amazingly attuned to it We should record in stereo ... or even ORTF (binaural) listen to an example

3. Microphones

Microphones

Even more critical in the digital era quality increase mics are analogue

Types dynamic vs

condenser mono, stereo,

binaural directionality

OMNI

... Microphones

CARDIOID

... Microphones

DIRECTIONAL/

SHOTGUN/

HYPERCARDIOID

ORTF

17cm

110°

... Microphones

Quality Placement

locating mounting and handling

... Microphones

Connections and cablesplugstypes of cableswiring for multiple, stereo/mono

PricesPower sources

see http://www.hrelp.org/archive/advice/microphones.html

Microphone usage principles

Monitor what you will record and what you are recording and what you recorded

The Inverse square law is your friend

4. Recorders

Recorders

Recorders in context Types and their

strengths/weaknesses/implications Quality parameters

accuracy (freq response, distortion, s/n ratio) reliability features versatility battery life and power sources

... Recorders

ConnectionsMedia types, costs, properties, implicationsFormats (see later)

5. Methods and principles

Methods

Quick guide to settings – levels, formats, AGCA second recorder?Using assistanceMonitorRehearsalPlayback to participantsCopying and backupHandling and re-using media

General principles

Consistency principlejuxtapositionsoptimise use of equipmentefficient processing

Microphone choiceMonitoringFamiliarity and skills with equipmentPower and batteriesA range of equipment, not the “perfect item”!

6. Audio signals

Audio properties

First analogue... then digital

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 at 120) each 6 dB step perceived as doubling/halving volume

... Signal parameters

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

Digital means sampling (measuring) where and when that is donesampling ratesample resolution (bit depth)bit rate (for compressed data)mono vs stereo

... Signal parameters

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

7. Today’s practical

Today’s practical

Aim: to create a set of recordingsto compare equipment and processes with outcomesto evaluate later (and perhaps to transcribe)

In groups, make a rough planroleswhat to recordequipment?

When you recordbe aware; try to anticipate the resultcollect some metadata

8. Defining digital audio

Digital audio

Analogue Digital (identify and measure points)

... Digital audio

0 20 40 60 80 100-100

000

1000

0

nominal time

ampl

itude

o

o

o

o

o

o

o

o

o

o

o

o

o

o

o

o

o

o

o

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Resolution

Sample rate (Hz) Sample size (bits) What do they mean?

11KHz, 8 bit 44.1 KHz, 16 bit 48 KHz, 24 bit 192 KHz, 48 bit

Implications for quality file size compatibility, usage ...

Encoding

“Codecs”File formats

9. Compression

CompressionReasonsTypes

open and proprietary formats (eg MP3 vs ATRAC)lossy and non-lossy (most are lossy)repeated compression unpredictable

Remember to distinguish sound information content from its encoding and its carrier

Compression

10. Carriers

So you’ve recorded some audio?

Carrier types label ... or not preserve track use of content

You may or may not need to digitise/redigitise/capture it

11. Digitising

Digitising

Where is it actually done?Involves either

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

Digitising

Where were your recordings digitised?

Digitisation: results and quality

What does the result depend on?player and digitising devicessettingslevelscables, connections, environment

Digitisation: results and quality

So where can quality be lost?(ignoring original recording issues)poor treatment of carriersunknown properties of carriers (unlabeled etc)choice of output port, settings (level, format etc)choice of input port, settings etcquality of player and digitising devicesconnections/cables, interference from other devices

or mains supply

Files

NamingVersions

12. Editing and converting

Editing

Why?selectmodify content“sweeten” for productionrestore, e.g. remove hum, hiss etc.create products

SoftwareAudacity, Audition, SoundForge, Peak LE

Converting

Why?What

Sample rate Sample size (bit depth)EncodingCompression

} all different parameters

13. Principles

Some broad principles

Evaluate and compare (use decent closed headphones)

Keep originals at original resolutionDon’t “upsample” or convert compressed

materialUnderstand the basics of the maths, esp files

sizes (orders of magnitude!)Find uses for audio!