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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?