Recording sound: environment,
people, equipment
Tom Castle
Bernard Howard
David Nathan
Outline
1. Situations
2. Psychoacoustics and
sound stage
3. Microphones
4. Recorders
5. Methods and
principles
6. Audio signals
7. Defining digital audio
8. Compression
9. Carriers
10. Digitisation
11. Editing and converting
12. Principles
13. Today’s practical
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 time
face away
use damping materials
see also General principles
kids
get them involved
show something to satisfy curiosity
animals
choose time of day
see 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 intermittently
Turn off
Avoid!
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 unwanted
Your brain recognises and rejects sounds
Recording process removes information
Therefore you need to optimise recording process at
point of capturing sound
“Sound stage”
Listening as a “hallucination”
Purpose of audio - for a human listener, who has:
ears
brain
location in physical world
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
110°
17cm
... Microphones
 Quality
 Placement
 locating
 mounting and handling
... Microphones
Connections and cables
plugs
types of cables
wiring for multiple, stereo/mono
Prices
Power 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
Let’s experiment
Listening practical session
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
Connections
Media types, costs, properties, implications
Formats (see later)
5. Methods and principles
Methods
Quick guide to settings – levels, formats, AGC
A second recorder?
Using assistance
Monitor
Rehearsal
Playback to participants
Copying and backup
Handling and re-using media
General principles
Consistency principle
juxtapositions
optimise use of equipment
efficient processing
Microphone choice
Monitoring
Familiarity and skills with equipment
Power and batteries
A 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 done
sampling rate
sample 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. Defining digital audio
Digital audio
Analogue
points)
Digital (identify and
measure
amplitude
-10000
0
10000
... Digital audio
o
o
o
o
o
o
o
o
0
o
o
o
o
40
o
o
o
o
20
o
o
o
60
nominal time
80
o
o
100
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
8. Compression
Compression
Compression
Reasons
Types
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
9. 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
10. 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 devices
settings
levels
cables, connections, environment
Digitisation: results and quality
So where can quality be lost?
(ignoring original recording issues)
poor treatment of carriers
unknown properties of carriers (unlabeled etc)
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
Files
Naming
Versions
11. Editing and converting
Editing
Why?
select
modify content
“sweeten” for production
restore, e.g. remove hum, hiss etc.
create products
Software
Audacity, Audition, SoundForge, Peak LE
Converting
Why?
What
Sample rate
Sample size (bit depth)
Encoding
Compression
}
all different parameters
12. Principles
Some broad principles
Evaluate and compare (use decent closed
headphones)
Keep originals at original resolution
Don’t “upsample” or convert compressed material
Understand the basics of the maths, esp files sizes
(orders of magnitude!)
Find uses for audio!
13. Practical
Practical
Aim: to create a set of recordings
to compare equipment and processes with outcomes
to evaluate later (and perhaps to transcribe)
In groups, make a rough plan
roles and equipment
what to record
metadata
When you record
be aware; try to anticipate the result
collect metadata