Transcript Sound 2

Multimedia Authoring
Introduction to Garageband
Garageband is both a:
• MIDI sequencer
• Digital audio recorder
Garageband: Real Instruments
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Tracks displayed in purple, recorded from real instruments
Can copy and paste, chop pieces out
Cannot transpose them (play back at different pitch)
Cannot change tempo (play back faster or slower)
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Multimedia Authoring
Introduction to Garageband
Garageband: Software Instruments
• Green tracks were created on a MIDI instrument
• Can record keyboard performances, display performance
bars as a grid (like a piano roll)
• Can edit notes, correct mistakes
• Drag notes higher or lower
• Make them last longer or shorter
• Delete unwanted notes
• Can transpose a piece (change key so it is higher or lower)
• Can speed up or slow down the performance
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Audio File Formats
There are many file formats for storing audio files.
It is important to distinguish between file format and codec, even
though most audio file formats support only one audio codec, a
file format may support multiple codecs.
Two major groups - lossless and lossy.
•lossless: WAV, PCM, TTA, FLAC, AU, AIFF
TTA: 2:1 compression - no data / quality lost in codec
•lossy compression: MP3, Ogg Vorbis (OGG), Windows Media
Audio (WMA), AAC
These are based on psychoacoustic models cutting out sounds we
cannot hear - MP3
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Audio File Formats
AIFF
Audio Interchange File Format (AIFF)
•developed by Apple for storing sound in the data fork of Macintosh files
Macs use a unique dual-fork file structure - resources in one fork - data in
another
•not cross platform, not supported by all web browsers
•very big
•adopted as a standard audio format by the Open Media Format Interchange
(OMFI) group for cross-platform media exchange (includes Silicon Graphics,
Avid Technology)
•GarageBand and Mac-based professional digital audio recording systems - also
Audacity import and export
•stores audio mono or stereo 16-bit, 8-bit and wide range sample rates
•have extension .aif or .iff
•there is another format called AIFF-C (compressed) that gives up to 6:1
compression - also AIFC
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Audio File Formats
WAV
WAVE File Format is a file format for storing digital audio (waveform)
data.
•supports a variety of bit resolutions, sample rates, channels of audio
•Windows native file format for storing digital audio data - vey popular
on PC platforms
•widely used in professional programs - popularity of Windows
•takes into account some peculiarities of the Intel CPU such as little
endian byte order
low order byte of a number stored at lowest address
•almost every program that can open or save digital audio support this
format
•very useful, flexible
•good for storing and archiving original recordings
•based on RIFF file format - similar to AIFF
•Freeware wav files
(http://simplythebest.net/sounds/WAV/sound_effects_WAV/ )
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Audio File Formats
OGG - compressed
Ogg Vorbis is an open, patent-free, professional audio
encoding and streaming technology
•Open Source
•new audio compression format - roughly comparable
to MP3
•vorbis - name of the audio compression scheme
http://www.vorbis.com
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Audio File Formats
MP3 - compressed
•Uses the MPEG audio layer 3 codec to provide acceptable lossy
compression for music files.
•compression about 1:10 compared with uncompressed WAV
files
•MP3 movement an amazing phenomenon - started with a huge
audience of music lovers on the Internet, not with the music
industry itself
•huge impact on how people collect, listen to, and distribute
music
•some sounds we hear much better than others - if both playing
at the same time remove the one our ears ignore
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Audio File Formats
WMA - compressed
Windows Media Audio format
•Microsoft
•Advanced Systems Format (.asf) files
•Container format
•Specifies structure of audio/video stream
•Metadata
•Optimized for streaming media
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Audio File Formats
AAC
Advanced Audio Coding (AAC) - used by iTunes
Since the 1990s, movie theatres have upgraded their
sound systems to surround sound systems.
•carry more than two channels
•codec copyrighted - encoders / decoders cannot
be offered without paying a licence fee
•most popular format - 5.1 ( 3 front, 2 back +
subwoofer for low frequencies - our ears cannot
tell where the low frequencies come from)
•Dolby Digital uses a similar codec (AC-3)
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Multimedia Authoring
Bringing an Audio Recording into your
Multimedia Project
1. Determine the file formats that are compatible
with your multimedia authoring software and the
delivery medium(s) you will be using (for file
storage and bandwidth capacity)
2. Determine the sound playback capabilities
(codecs and plug-ins) that the end user’s system
offers
3. Decide what kind of sound is needed e.g.
background music, special effects, spoken
dialogue
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Multimedia Authoring
Bringing an Audio Recording into your
Multimedia Project
4. Decide where and when you want to use either
digital audio or MIDI data
5. Acquire source material by creating it from
scratch or purchasing it
6. Edit the sounds to fit your project
7. Test the sounds to be sure that they are timed
properly with the project’s images.
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Digital Audio
Space Considerations
It takes about 1.94 MB to store 11 seconds of
uncompressed Red Book stereo sound.
Ideas for Reducing Storage Requirements
• Is mono sound acceptable?
• Use compression
• Try downsampling
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Digital Audio
Calculating Storage Needs
Sample rate*sample size/8*#seconds*channels =?KB
Example
You have been assigned to design and produce the audio
portions of a multimedia project. The program will be delivered
on a CD-ROM, and video clips will take up most of the CD.
You have only 50MB of storage space to store 20 one-minute
clips of speech, 10 songs averaging three minutes long, and a
background sound loop. What sampling rates and depths should
you use for the speech, for the music, and for the
background sound? Why? Roughly calculate the file size totals
for these specifications, and be sure that you end up with less
than the 50MB of storage space allotted. Discuss your
reasoning.
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Digital Audio
References
Vaughan, T. (2011) Multimedia: Making It Work, 8th
Ed. , New York: McGraw-Hill
Savage, S. (2011) The Art of Digital Audio
Recording, Oxford: Oxford University Press
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