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CEN-444
Networks Structure And Protocols
SOUND
Mohammed Saleem Bhat
[email protected]
Computer Engineering and Networks, College of Engineering , Majmaah University
Overview
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Introduction to sound.
Multimedia system sound.
Digital audio.
MIDI audio.
Audio file formats.
Computer Engineering and Networks, College of Engineering , Majmaah University
Overview
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MIDI versus digital audio.
Adding sound to multimedia project.
Professional sound.
Production tips.
Computer Engineering and Networks, College of Engineering , Majmaah University
Power of Sound
• Vibrations in the air create waves of pressure that are
perceived as sound.
• Sound waves vary in sound pressure level
(amplitude) and in frequency or pitch.
• ‘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 (see p.
91)
Computer Engineering and Networks, College of Engineering , Majmaah University
Sound
• Sound is energy, caused by molecules
vibrating
• Too much volume can permanently damage
your ears and hearing
• The perception of loudness depend on the
frequency or pitch
• Harmonics cause the same note played on a
cello to sound different from one played on
a piano.
Computer Engineering and Networks, College of Engineering , Majmaah University
Using Sound in Multimedia
• You need to know
– How to make sounds
– How to record and edit sounds on the computer
– How to incorporate sounds into your multimedia
project
Computer Engineering and Networks, College of Engineering , Majmaah University
Multimedia System Sounds
• System sounds are assigned to various system
events such as startup and warnings, among
others.
• Macintosh provides several system sound options
such as glass, indigo, laugh.
• In Windows, available system sounds include
start.wav, chimes.wav, and chord.wav.
• Multimedia sound is either digitally recorded
audio or MIDI (Musical Instrumental Digital
Interface) music.
Computer Engineering and Networks, College of Engineering , Majmaah University
Multimedia System Sounds
• Most computers have sounds ready to use
Computer Engineering and Networks, College of Engineering , Majmaah University
Multimedia System Sounds
• Mac and Windows have built in sound
recorders
Computer Engineering and Networks, College of Engineering , Majmaah University
Multimedia System Sounds
• Windows system sounds are .WAV files in the
Windows\Media directory
• MS Office includes additional sounds
• You can add your own sounds by including
them in the Windows\Media directory and
selecting them from the Sound Control Panel
Computer Engineering and Networks, College of Engineering , Majmaah University
MIDI Audio
• MIDI is a series of musical instructions
Click to play
Computer Engineering and Networks, College of Engineering , Majmaah University
MIDI vs. Digital Audio
• MIDI ( Musical Instrument Digital Interface)
is a communications standard developed in the
1980’s for electronic instruments and
computers.
• It allows instruments from different
manufacturers to communicate.
Computer Engineering and Networks, College of Engineering , Majmaah University
MIDI vs. Digital Audio
• MIDI data is NOT digitized sound- it is music 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 sound system
• Quality depends on end user’s device rather than on
the MIDI device and is device dependent.
Computer Engineering and Networks, College of Engineering , Majmaah University
Making MIDI Audio
• Creating a MIDI score requires:
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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
Computer Engineering and Networks, College of Engineering , Majmaah University
Making MIDI Audio
You will need:
• Sequencer Software (Smart Score)
• A Sound synthesizer ( built into PC sound
board, an add on for MAC)
• MIDI keyboard or device
• Ability to play the piano and music theory
background
• or a hired “expert”
Computer Engineering and Networks, College of Engineering , Majmaah University
MIDI
• A MIDI file is a list of commands that are
recordings of musical actions, that when sent
to a MIDI player results in sound
• MIDI data is device dependent
• MIDI represents musical instruments and is
not easily used to playback spoken dialog
Computer Engineering and Networks, College of Engineering , Majmaah University
MIDI Audio
• MIDI is a shorthand representation of music 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 pitch of the music or degrading audio
quality.
• Working with MIDI requires knowledge of music
theory.
Computer Engineering and Networks, College of Engineering , Majmaah University
Digital Audio
• Digital audio is a representation of the
original sound
• Sampling rate is measured in kilohertz
(kHz)
Click to play
Computer Engineering and Networks, College of Engineering , Majmaah University
Digital Audio
• Digital audio represents a sound stored in
thousands of numbers or samples.
• Digital data represents the loudness at
discrete slices of time.
• It is NOT device dependent and should
sound the same each time it is played
• It is used for music CD’s
Computer Engineering and Networks, College of Engineering , Majmaah University
Digital Audio
• The three sampling frequencies most often used in
multimedia are CD-quality 44.1 kHz, 22.05 kHz
and 11.025 kHz.
• The number of bits used to describe the amplitude
of sound wave when sampled, determines the
sample size.
• Digital audio is device independent.
• The value of each sample is rounded off to the
nearest integer (quantization).
Computer Engineering and Networks, College of Engineering , Majmaah University
Preparing Digital Audio
• Balance file size versus quality
• Set recording levels
• Edit the recording
Computer Engineering and Networks, College of Engineering , Majmaah University
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
Computer Engineering and Networks, College of Engineering , Majmaah University
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.
Computer Engineering and Networks, College of Engineering , Majmaah University
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.
Computer Engineering and Networks, College of Engineering , Majmaah University
MIDI vs. Digital Audio
• MIDI data and digital audio are like vector and
bitmapped graphics:
• Digital audio like bitmapped image – samples
original to create a copy
• MIDI – like vector graphic- stores numeric
data to recreate sound
Computer Engineering and Networks, College of Engineering , Majmaah University
MIDI vs. Digital Audio
• MIDI data is device dependent; digital audio is
not
• MIDI sounds (like vector graphics) are
different on different devices;
• Digital sounds are identical even on different
computers or devices.
Computer Engineering and Networks, College of Engineering , Majmaah University
MIDI Advantages
• MIDI file are much more compact and take
up less memory and system resources
• MIDI files embedded in web pages load and
play much faster than digital
• You can change the length of a MIDI file by
varying its tempo
• With high quality MIDI devices, MIDI files
may actually sound better than digital
Computer Engineering and Networks, College of Engineering , Majmaah University
MIDI Disadvantages
• MIDI represents musical instruments not
sounds and will be accurate only if your
playback device is identical to the production
device
• MIDI sound is inconsistent
• MIDI cannot be easily used to reproduce
speech
Computer Engineering and Networks, College of Engineering , Majmaah University
Digital Audio Advantages
• Digital audio sound is consistent and device
independent
• A wide selection of software support is
available for both MAC and PC
• A knowledge of music theory is not required
for creating digital audio, but usually is needed
for MIDI production
Computer Engineering and Networks, College of Engineering , Majmaah University
Choose MIDI data
• If you don’t have enough RAM memory, or
bandwidth for digital audio
• If you have a high quality sound source
• If you have complete control over the playback
hardware
• If you don’t need spoken dialog
Computer Engineering and Networks, College of Engineering , Majmaah University
Choose Digital Audio
• If you don’t have control over the playback
hardware
• If you have the computing resources and
bandwidth to handle the larger digital files
• If you need spoken dialog
Computer Engineering and Networks, College of Engineering , Majmaah University
Digital Audio
• You can digitize sound from a microphone,
synthesizer, tape recording TV broadcast, or
CD’s.
• Digitized sound is sampled every nth of a
second. The more often you take the sample,
the better the sound.
• Sample sizes are either 8 or 16 bits and
common frequencies are11.025, 22.05, and
44.1 kHz (See pp. 209- 211)
Computer Engineering and Networks, College of Engineering , Majmaah University
Digital Audio
• To prepare digital audio from analog media,
record it from a device, like a tape recorder,
into your computer using digitizing software.
• Balance the sound quality with your available
RAM
• Set proper recording levels for a good clear
recording
Computer Engineering and Networks, College of Engineering , Majmaah University
File Size vs. Quality
• Audio resolution determines the accuracy
with which a sound is digitized. (More bits
in the sample size produces better quality
and larger files)
• Stereo recordings are more realistic and
require twice as much storage space and
playback time.
• Mono files tend to sound “flat”
Computer Engineering and Networks, College of Engineering , Majmaah University
Editing Digital Recordings
• Apple’s QuickTime Player Pro provides for
primitive playback and editing
• Sonic Foundry’s Sound Forge is a more
serious sound editor
• These can be used to trim, splice, volume
adjustment and format conversion as well as
special effects
Computer Engineering and Networks, College of Engineering , Majmaah University
Audio File Formats
• A sound file’s format is a recognized methodology
for organizing data bits of digitized sound into a
data file.
• On the Macintosh, digitized sounds may be stored
as data files, resources, or applications such as
AIFF or AIFC.
• In Windows, digitized sounds are usually stored as
WAV files.
• Both can use MIDI files (.mid)
Computer Engineering and Networks, College of Engineering , Majmaah University
Audio File Formats
• CD-ROM/XA (Extended Architecture) format
enabled several recording sessions to be placed
on a single CD-R (recordable) disc.
• Linear Pulse Code Modulation is used for Red
Book Audio data files on consumer-grade
music CDs.
Computer Engineering and Networks, College of Engineering , Majmaah University
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 and
playing it while it downloads
• Streaming is dependent on the connection
speed
• FLASH allows sound to be integrated in a
multimedia presentation, controlled by
buttons and saved as .mp3
Computer Engineering and Networks, College of Engineering , Majmaah University
Adding Sound to a
Multimedia Project
• Decide what sounds you will need and
include them in the story board or cue sheet.
• Decide whether to use MIDI or digital audio
• Acquire source material (record/buy)
• Edit the sounds
• Test the sounds to be sure they are timed
properly
Computer Engineering and Networks, College of Engineering , Majmaah University
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
Computer Engineering and Networks, College of Engineering , Majmaah University
Professional Sound
• The Red Book Standard- ISO 10149
– ( 16 bits at 44.1 kHz) allows accurate reproduction
of all sounds humans can hear
– Software such as Toast and CD-Creator can
translate digital files from CD’s directly into a
digital sound editing file or decompress.mp3 files
into CD-Audio
Computer Engineering and Networks, College of Engineering , Majmaah University
Professional Sound
• Compression techniques reduce space but
reliability suffers.
• Space can be conserved by downsampling or
reducing the number of sample slices taken per
second.
• File size of digital recording (in bytes) = sampling
rate X duration of recording (in secs) X (bit
resolution/8) X number of tracks.
Computer Engineering and Networks, College of Engineering , Majmaah University
Advanced Sound Management
• Scripting Languages such as Open Script
(Toolbook), LINGO(Director), or Action
Script ( FLASH) provide better control over
audio playback
• Requires some programming knowledge
Computer Engineering and Networks, College of Engineering , Majmaah University
Production Tips
• Vaughn’s Law of Minimums - there is an
acceptable level of adequacy that will satisfy
the audience;
• If your handheld microphone is good enough
to satisfy you and your audience, conserve
your money and energy.
Computer Engineering and Networks, College of Engineering , Majmaah University
Production Tips
• Recording on inexpensive media rather
than directly to disk prevents the hard
disk from being overloaded with
unnecessary data.
• The equipment and standards used for
the project must be in accordance with
the requirements.
• Sound and image synchronization must
be tested at regular intervals
Computer Engineering and Networks, College of Engineering , Majmaah University
Production Tips
• Audio recording - use CD’s, or VCR tapes, or
DAT ( digital audio tape) tapes
• Create a good database to organize your
sounds, noting the counter and content
• Testing and Evaluating- (delaying a fast
machine if needed to sync with animation)
Computer Engineering and Networks, College of Engineering , Majmaah University
Production Tips
• Copyright Issues
• Securing permission for the use of sounds and
music is the same as for images
• Can buy royalty-free digitized sound clips
• DO NOT use someone’s original work without
permission!
Computer Engineering and Networks, College of Engineering , Majmaah University
Summary
• Vibrations in air create waves of pressure that are
perceived as sound.
• Multimedia system sound is digitally recorded audio
or MIDI (Musical Instrumental Digital Interface)
music.
• Digital audio data is the actual representation of a
sound, stored in the form of samples.
Computer Engineering and Networks, College of Engineering , Majmaah University
Summary
• MIDI is a shorthand representation of music
stored in numeric form.
• Digital audio provides consistent playback quality.
• MIDI files are much smaller than digitized audio.
• MIDI is device dependent digital audio is not
• MIDI files sound better than digital audio files
when played on high-quality MIDI device.
Computer Engineering and Networks, College of Engineering , Majmaah University