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2/16/2011
COM 205
Multimedia Programming
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2/16/2011
Chapter 5
Sound
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Overview
Introduction to sound.
Multimedia system sound.
Digital audio.
MIDI audio.
Audio file formats.
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Overview
MIDI versus digital audio.
Adding sound to multimedia project.
Professional sound.
Production tips.
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Power of Sound
Vibrations in the air create waves ofpressure that are perceived as sound.
Sound waves vary in sound pressure level
(amplitude) and in frequency. Acoustics is the branch of physics that
studies sound.
Sound pressure levels (loudness or
volume) are measured in decibels (dB). Humans hear sound over a very broad
range
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Sound
Sound is energy, caused bymolecules vibrating
Too much volume can permanently
damage your ears and hearing The perception of loudness depend
on the frequency
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Using Sound in Multimedia
You need to know
How to make sounds
How to record and edit sounds on thecomputer
How to incorporate sounds into yourmultimedia project
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Multimedia System Sounds
System sounds are assigned to varioussystem events such as startup andwarnings, among others.
Macintosh provides several system soundoptions such as glass, indigo, laugh.
In Windows, available system soundsinclude start.wav, chimes.wav, and
chord.wav.
Multimedia sound is either digitallyrecorded audio or MIDI (Musical
Instrumental Digital Interface) music.
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Multimedia System Sounds
Most computers have sounds readyto use
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Multimedia System Sounds
Mac and Windows have built insound recorders
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MIDI Audio
MIDI is a series of musicalinstructions
Click to play
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MIDI vs. Digital Audio
MIDI ( Musical Instrument DigitalInterface) is a communicationsstandard developed in the 1980s forelectronic instruments andcomputers.
It allows instruments from differentmanufacturers to communicate.
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MIDI vs. Digital Audio
MIDI data is NOT digitized sound- it ismusic stored in numeric format
Digital audio is a recording, which depend
on your sound system MIDI is a score and depends on both the
quality of the instruments and the soundsystem
Quality depends on end users devicerather than on the MIDI device and isdevice dependent.
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Making MIDI Audio
Creating a MIDI score requires: Knowledge of music and some talent
Ability to play a musical instrument
Sequencer software
Sound synthesizer Built into PC board
Add-on for MAC
MIDI can synthesize over 100 instruments
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Making MIDI Audio
You will need:
Sequencer Software (Smart Score)
A Sound synthesizer ( built into PCsound board, an add on for MAC)
MIDI keyboard or device
Ability to play the piano and musictheory background
or a hired expert
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MIDI
A MIDI file is a list of commands thatare recordings of musical actions,that when sent to a MIDI playerresults in sound
MIDI data is device dependent
MIDI represents musical instrumentsand is not easily used to playbackspoken dialog
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MIDI Audio
MIDI is a shorthand representation ofmusic stored in numeric form.
Since they are small, MIDI files embedded
in web pages load and play promptly. Length of a MIDI file can be changed
without affecting the frequency of themusic or degrading audio quality.
Working with MIDI requires knowledge ofmusic theory.
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Digital Audio
Digital audio is a representationof the original sound
Sampling rate is measured inkilohertz (kHz)
Click to play
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Digital Audio
Digital audio represents a soundstored in thousands of numbers orsamples.
Digital data represents theloudness at discrete slices of time.
It is NOT device dependent and
should sound the same each time itis played
It is used for music CDs
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Digital Audio
The three sampling frequencies most oftenused in multimedia are CD-quality 44.1kHz, 22.05 kHz and 11.025 kHz.
The number of bits used to describe theamplitude of sound wave when sampled,determines the sample size.
Digital audio is device independent.
The value of each sample is rounded off tothe nearest integer (quantization).
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Preparing Digital Audio
Balance file size versusquality
Set recording levels
Edit the recording
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Preparing Digital Audio
Balance file size versus quality
To calculate file size in bytes:
Mono: sampling rate duration of recording
in seconds (bit resolution 8) 1
Stereo: sampling rate duration of recording
in seconds (bit resolution 8) 2
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Digital Audio Editing
Once a recording had been completed, it
almost always needs to be edited.
Basic sound editing operations include:
trimming, splicing and assembly, volume
adjustments and working on multiple
tracks.
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Digital Audio Editing
Additional available sound editing
operations include format conversion,
resampling or downsampling, fade-ins and
fade-outs, equalization, time stretching,
digital signal processing, and reversing
sounds.
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MIDI vs. Digital Audio
MIDI data and digital audio are likevector and bitmapped graphics:
Digital audio like bitmapped imagesamples original to create a copy
MIDI like vector graphic- storesnumeric data to recreate sound
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MIDI vs. Digital Audio
MIDI data is device dependent; digitalaudio is not
MIDI sounds (like vector graphics)are different on different devices;
Digital sounds are identical even ondifferent computers or devices.
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MIDI Advantages
MIDI file are much more compact andtake up less memory and systemresources
MIDI files embedded in web pagesload and play much faster than digital
You can change the length of a MIDIfile by varying its tempo
With high quality MIDI devices, MIDIfiles may actually sound better thandigital
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MIDI Disadvantages
MIDI represents musical instrumentsnot sounds and will be accurate onlyif your playback device is identicalto the production device
MIDI sound is inconsistent
MIDI cannot be easily used toreproduce speech
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Digital Audio Advantages
Digital audio sound is consistent anddevice independent
A wide selection of software supportis available for both MAC and PC
A knowledge of music theory is notrequired for creating digital audio,but usually is needed for MIDIproduction
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Choose MIDI data
If you dont have enough RAM
memory, or bandwidth for digitalaudio
If you have a high quality soundsource
If you have complete control over theplayback hardware
If you dont need spoken dialog
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Choose Digital Audio
If you dont have control over the
playback hardware
If you have the computing resourcesand bandwidth to handle the largerdigital files
If you need spoken dialog
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Digital Audio
You can digitize sound from amicrophone, synthesizer, taperecording TV broadcast, or CDs.
Digitized sound is sampled every nthof a second. The more often you takethe sample, the better the sound.
Sample sizes are either 8 or 16 bitsand common frequencies are11.025,22.05, and 44.1 kHz (See pp. 209- 211)
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Digital Audio
To prepare digital audio from analogmedia, record it from a device, like atape recorder, into your computerusing digitizing software.
Balance the sound quality with youravailable RAM
Set proper recording levels for agood clear recording
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File Size vs. Quality
Audio resolution determines theaccuracy with which a sound isdigitized. (More bits in the sample
size produces better quality andlarger files)
Stereo recordings are more realistic
and require twice as much storagespace and playback time.
Mono files tend to sound flat
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Editing Digital Recordings
Apples QuickTime Player Proprovides for primitive playback andediting
Sonic Foundrys Sound Forge is amore serious sound editor
These can be used to trim, splice,
volume adjustment and formatconversion as well as special effects
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Audio File Formats
A sound files format is a recognizedmethodology for organizing data bits ofdigitized sound into a data file.
On the Macintosh, digitized sounds maybe stored as data files, resources, orapplications such as AIFF or AIFC.
In Windows, digitized sounds are usuallystored as WAV files.
Both can use MIDI files (.mid)
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Audio File Formats
CD-ROM/XA (Extended Architecture)format enabled several recordingsessions to be placed on a single
CD-R (recordable) disc.
Linear Pulse Code Modulation isused for Red Book Audio data files
on consumer-grade music CDs.
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Sound for the World Wide Web
To play MIDI sound on the web wait for the entire file to download and
play it with a helper application
stream the file, storing it in the buffer andplaying it while it downloads
Streaming is dependent on theconnection speed
FLASH allows sound to be integratedin a multimedia presentation,controlled by buttons and saved as
.mp3
Adding Sound to a
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Adding Sound to a
Multimedia Project
Decide what sounds you will need andinclude them in the story board or cuesheet.
Decide whether to use MIDI or digitalaudio
Acquire source material (record/buy)
Edit the sounds
Test the sounds to be sure they aretimed properly
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Adding sound to Multimedia
CD- quality audio
Standard is ISO 10149, a.k.a. the Red Book Standard
Sample size is 16-bit
Sample rate is 44.1 kHz
11 seconds of audio uses 1.94 MB of space
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Professional Sound
The Red Book Standard- ISO 10149
( 16 bits at 44.1 kHz) allows accuratereproduction of all sounds humans can
hear
Software such as Toast and CD-Creatorcan translate digital files from CDs
directly into a digital sound editing fileor decompress.mp3 files into CD-Audio
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Professional Sound
Compression techniques reduce space butreliability suffers.
Space can be conserved by downsampling
or reducing the number of sample slicestaken per second.
File size of digital recording (in bytes) =sampling rate X duration of recording (insecs) X (bit resolution/8) X number oftracks.
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Advanced Sound Management
Scripting Languages such as OpenScript (Toolbook), LINGO(Director),or Action Script ( FLASH) provide
better control over audio playback
Requires some programmingknowledge
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Production Tips
Vaughns Law of Minimums - there isan acceptable level of adequacy thatwill satisfy the audience;
If your handheld microphone is goodenough to satisfy you and youraudience, conserve your money and
energy.
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Production Tips
Recording on inexpensive mediarather than directly to diskprevents the hard disk from being
overloaded with unnecessary data.
The equipment and standardsused for the project must be in
accordance with the requirements.
Sound and image synchronizationmust be tested at regular intervals
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Production Tips
Audio recording - use CDs, or VCRtapes, or DAT ( digital audio tape)tapes
Create a good database to organizeyour sounds, noting the counter andcontent
Testing and Evaluating- (delaying afast machine if needed to sync withanimation)
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Production Tips
Copyright Issues
Securing permission for the use ofsounds and music is the same as forimages
Can buy royalty-free digitized soundclips
DO NOT use someones original
work without permission!
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Summary
Vibrations in air create waves of pressurethat are perceived as sound.
Multimedia system sound is digitally
recorded audio or MIDI (MusicalInstrumental Digital Interface) music.
Digital audio data is the actualrepresentation of a sound, stored in theform of samples.
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Summary
MIDI is a shorthand representation ofmusic stored in numeric form.
Digital audio provides consistent playbackquality.
MIDI files are much smaller than digitizedaudio.
MIDI is device dependent digital audio isnot
MIDI files sound better than digital audiofiles when played on high-quality MIDIdevice.