Transcript Information about sound recording

Week 10: Audio Recording
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Overview
What is sound?
What does analogue mean?
Analogue-to-Digital conversion
Key terms in digital audio
Compression
Formats
Audacity demo
Practical work
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What is sound?
Sound is created when an object vibrates
(moves back and forth), pushing the air
around it
sound is a variation in pressure
pressure 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:
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Mechanical displacement (microphone, speaker)
Voltage variations
Wiggles in vinyl record grooves
Degree of magnetisation on tape
Optical density in film
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Analogue wave patterns
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
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Working with audio
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)
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Working with audio
Process
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 Conversion
Measure an analogue signal periodically:
Store the measurements as a sequence of
numbers
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Key terms
Sampling Rate
how often analog signal is measured
samples per second, Hertz (Hz) or kilo Hertz
(kHz)
e.g. 44,100 or 44.1 kHz
Sampling Resolution
precision of numbers used for measurement:
the more bits, the higher the resolution
bit depth
e.g. 8 bit (1 byte), 16 bit (2 bytes) etc
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Digital to Audio Conversion
The 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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Common Sampling Rates
Humans hear variations from about 20Hz
to 20000Hz
Sampling Rate
Uses
44.1 kHz (44100)
CD, DAT
48 kHz (48000)
DAT, DV, DVD-Video
96 kHz (96000)
DVD-Audio
22.05 kHz (22050)
Old samplers
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Common Sampling Resolutions
Bit depth
Word length
Uses
8-bit integer
Low-res web audio
16-bit integer
CD, DAT, DV, sound files
24-bit integer
DVD-Video, DVD-Audio
32-bit floating point Software (usually only for
internal representation)
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File Size
1 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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Compression
Audio 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
WAV
AU
MP3
WMA
ASF
RA
AIFF
Windows native file format
Sun audio file (Unix)
MPEG layer III compressed audio
Windows media audio
Microsoft advanced streaming format
Real Audio compressed streaming data
Audio 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 from
Copyright 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 Audacity
Premiere uses Smartsound to create
seamless loops
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Hardware required to capture audio
Sound Card
Microphone
External devices
 Mini disc
 MP3 players
 Keyboard
Speakers
 headphones also useful
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Recording issues
Avoid background noise
Use a headset with an attached
microphone for voice recording
leaves your hands free and keeps the
microphone at a fixed distance from the mouth
Position the microphone to the side of the
mouth, not in front
Check the sound levels
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Audacity
Free open source software
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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 Interface
Video 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?
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