Recording sound: people, environment and equipment Tom Castle David Nathan Rob Kennedy
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
o
o
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!