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Recording sound: people, environment and equipment Tom Castle David Nathan Rob Kennedy
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Outline 1.Situations 2.Psychoacoustics and sound stage 3.Microphones 4.Recorders 5.Methods and principles 6.Audio signals 7.Today’s practical 8.Defining digital audio 9.Compression 10.Carriers 11.Digitisation 12.Editing and converting 13.Principles
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1. Situations
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Situations (External) environment access electricity external noise sources
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... Environment (ext) external noise sources (cont’d) examplepossibilities 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
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Environment (close-up) Internal environment Machines examplepossibilities for dealing with it Refrigerator Survey what comes on intermittently Turn off Avoid! Motors, switching Avoid electrical interference Fans Unexpected noise introduced
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... 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
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2. Psychoacoustics and sound stage
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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 Vision for your ears Your brain recognises and rejects sounds Recording process removes many cues Therefore need to optimise recording process at point of capturing sound waves
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“Sound stage” Listening as a “hallucination” Purpose of audio - for a human listener, who has: ears brain spatial location Our normal approach to recording is unscientific; reduces events to data What is “fidelity”?
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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 ... or even ORTF (binaural) listen to an example
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3. Microphones
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Microphones Even more critical in the digital era quality increase mics are analogue Types dynamic vs condenser mono, stereo, binaural directionality OMNI
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... Microphones CARDIOID
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... Microphones DIRECTIONAL/ SHOTGUN/ HYPERCARDIOID
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ORTF 17cm 110°
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... Microphones Quality Placement locating mounting and handling
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... 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
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Microphone usage principles Monitor what you will record and what you are recording and what you recorded The Inverse square law is your friend
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4. Recorders
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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
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... Recorders Connections Media types, costs, properties, implications Formats (see later)
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5. Methods and principles
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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
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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”!
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6. Audio signals
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Audio properties First analogue ... then digital
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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
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... 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
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... Signal parameters Signal to noise ratio of wanted to unwanted sound data the bigger the number the better
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7. Today’s practical
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Today’s 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 what to record equipment? When you record be aware; try to anticipate the result collect some metadata
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8. Defining digital audio
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Digital audio AnalogueDigital (identify and measure points)
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... Digital audio
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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...
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Encoding “Codecs” File formats
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9. Compression
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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 Compression
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10. Carriers
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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
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11. Digitising
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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 were your recordings 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 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
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Files Naming Versions
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12. Editing and converting
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Editing Why? select modify content “sweeten” for production restore, e.g. remove hum, hiss etc. create products Software Audacity, Audition, SoundForge, Peak LE
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Converting Why? What Sample rate Sample size (bit depth) Encoding Compression } all different parameters
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13. Principles
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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!
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