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Week 10: Audio RecordingWeek 10: Audio Recording
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OverviewWhat is sound?
What does analogue mean?Analogue-to-Digital conversion
Key terms in digital audioCompressionFormats
Audacity demoPractical work
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What is sound?Sound is created when an object vibrates
(moves back and forth), pushing the air around itsound is a variation in pressurepressure variations travel through air as waves (hence the term sound waves)sound travels about 1000 feet/second
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What does analogue mean?Analogue audio signal follows the same pattern
as the vibration in air pressure caused by the original sound
Microphones turn audible sounds into electronic copies of those sounds
Pressure variations (sound) can be stored through: Mechanical displacement (microphone, speaker) Voltage variations Wiggles in vinyl record grooves Degree of magnetisation on tape Optical density in film
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Have three attributes:Wavelength
distance between any point on a wave and the equivalent point on the next phase (i.e. the length of the wave)
Amplitude the height of each peak in the sound wave higher amplitudes are interpreted as a higher volume
Frequency (pitch) number of times a wavelength occurs in one second measured in kilohertz (Khz), or cycles per second higher frequencies are interpreted as a higher pitch
Analogue wave patterns
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Audio systems are based around one simple concept: take sound waves, convert them into an electric current and manipulate
them as desired, then convert them back into sound waves
Transducer converts energy from one form into another microphones : convert acoustical energy into electrical energy speakers: convert electrical energy into acoustical energy
Amplifier a device which takes a signal and increases it's power (i.e. amplitude)
Working with audio
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Working with audioProcess
sound source creates waves of sound (acoustical energy)
waves are detected by a transducer (microphone) which converts them to electrical energy
electrical signal from the microphone is very weak, and must be fed to an amplifier before anything serious can be done with it
loudspeaker converts the electrical signal back into sound waves, which are heard by human ears
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Digital to Audio ConversionMeasure an analogue signal periodically:
Store the measurements as a sequence of numbers
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Key termsSampling Rate
how often analog signal is measuredsamples per second, Hertz (Hz) or kilo Hertz (kHz)e.g. 44,100 or 44.1 kHz
Sampling Resolutionprecision of numbers used for measurement: the
more bits, the higher the resolutionbit depthe.g. 8 bit (1 byte), 16 bit (2 bytes) etc
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Digital to Audio ConversionThe conversion process is not entirely perfect
Higher sampling rates produces closer fit (i.e. higher quality) at the expense of file size
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Humans hear variations from about 20Hz to 20000Hz
Old samplers22.05 kHz (22050)
DVD-Audio96 kHz (96000)
DAT, DV, DVD-Video48 kHz (48000)
UsesSampling Rate
CD, DAT44.1 kHz (44100)
Common Sampling Rates
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Bit depth
Software (usually only for internal representation)
32-bit floating point
DVD-Video, DVD-Audio24-bit integer
CD, DAT, DV, sound files16-bit integer
UsesWord length
Low-res web audio8-bit integer
Common Sampling Resolutions
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File Size1 minute of CD quality audio
Sampling rate: 44,100 samples per second (44.1 kHz) Sample resolution: 16 bits (i.e., 2 bytes) per sample Number of channels: 2 (stereo)
Gives 44,100 samples * 2 bytes per sample * 2 channels
= 176,400 bytes per second
60 seconds per minute 60 * 176,400 bytes per second
= 10584000 bytes ~ 10Mb per minute
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CompressionAudio compression consists of two parts:Encoding
transforms the digital audio data in a WAVE file, into a highly compressed form called a bitstream
throws away data not required to reduce the file size important to realise that the resulting compressed file is not the same as the original
digital version - a close copy
Decoding takes the bitstream and re-expands it to a WAVE file
Many different CODECS are available MP3 is a common standard (!) CODEC must exist on playback PC for decoding to work
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Common File Formats
WAVAUMP3WMAASFRAAIFF
Windows native file formatSun audio file (Unix)MPEG layer III compressed audioWindows media audioMicrosoft advanced streaming formatReal Audio compressed streaming dataAudio Interchange Format File (Mac)
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Channels of sound
Mono Stereo Dolby Pro Logic Dolby Digital 5.1 & 6.1 (Ex) DTS 5.1& 6.1 (Es)
More information (data) requires larger file sizes
Specialist software to edit
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Where to get audio fromCopyright free audio
downloads available from module web site magazine cover disks (credit source) Internet (credit source)
Royalty free audio (purchase) Media Tracks (www.media-tracks.com) $13 per clip AKM Music (www.akmmusic.co.uk) £35 per CD Partners in Rhyme (www.partnersinrhyme.com) free - $70 per collection
Create your own effects with AudacityPremiere uses Smartsound to create seamless
loops
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Hardware required to capture audioSound CardMicrophoneExternal devices
Mini disc MP3 players Keyboard
Speakers headphones also useful
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Recording issuesAvoid background noiseUse a headset with an attached
microphone for voice recordingleaves your hands free and keeps the
microphone at a fixed distance from the mouthPosition the microphone to the side of the
mouth, not in frontCheck the sound levels
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AudacityFree open source software
Easy to use Multi-track editing Effects Convert between different audio formats
Supports industry standard VST plug-ins (Virtual Studio Technology)
File type of .aup is the project file contains all the edit instructions
need to export to create the audio file for playback http://audacity.sourceforge.net
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Audacity InterfaceVideo demo
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Tutorial Devise the 250 word narrative/story for “Every house has its secret” Record the story using Audacity Edit into several audio clips for use in Flash
Use Audacity’s effects and mixing facilities + spot effects from… http://mmedia.glos.ac.uk/mu110/audio.htm
Develop the storyboard Scenes Sequencing within each scene
Swap with a partner Review the storyboard and identify any unclear elements Tutors will identify plenary items
Self Study Review the storyboard and finalise with annotations Review the Assignment Brief Must include: 1 or more graphic characters, animation, audio to
illustrate mood and change of pace Begin building the scenes in Illustrator/Flash
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Any questions?