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Chapter 5
Sound
Prepared by:
Ms. Ma. Anna Corina G. Kagaoan
College of Arts and Sciences
Objectives:
• Learn how to use sound in a
multimedia project;
• Learn how to use MIDI and
understand its attributes, especially
relative to digitized audio;
• Learn to calculate sampling sizes
and considerations for digitized
sound;
• Record, process, and edit digital
audio; and
• Determine which audio file formats
are best used in multimedia
projects.
Sound
• Perhaps the most sensuous element of multimedia.
• Meaningful “speech” in any language, from a whisper to
a scream.
• Can provide the listening pleasure of music, the
startling accent of special effects, or the ambience of a
mood-setting background.
• Some feel-good music powerfully fills the heart,
generating emotions of love or otherwise elevating
listeners closer to heaven.
• How the power of sound is used can make the
difference
between
and
ordinary
multimedia
presentation and professionally spectacular one.
• Misuse of sound, however, can wreck your project.
The Power of Sound
• Acoustics – the branch of physics that studies sound.
• Decibels (dB) – measure of sound pressure levels
(loudness or volume). The ratio between a chosen
reference point on a logarithmic scale and the level
that is actually experienced.
• Sound is energy. Too much volume can permanently
damage the delicate receiving mechanism behind your
eardrums.
• What you hear subjectively is not what you hear
objectively. The perception of loudness is dependent
upon the frequency or pitch of the sound. You may
feel the sound more than hear it.
Multimedia System Sounds
• WAV files – system sounds in Windows , they reside in
the Windows\Media subdirectory. Examples: start.wav,
chimes.wav,
ding.wav,
logoff.wav,
notify.wav,
recycle.wav, tada.wav and Microsoft sound.wav. You
can assign these sounds in system events such as
Windows startup, warnings, clicks, etc.
• AIF format – system sounds in OS X on Macintosh. You
can only change the system alert sound in this platform.
Custom sound files may be put into ~/Library/Sounds.
• Digitally recorded audio or MIDI (Musical Instrument
Digital Interface) – most sound used in multimedia
productions.
Digital Audio
• Created when sound wave is represented using
numbers—digitizing.
• Digitized sound is sampled sound. Every nth fraction of
a second, a sample of sound is taken and stored as
digital information in bits and bytes.
• Sampling rate or frequency – how often the samples
are taken. Measured in kilohertz, or thousands of
samples per second.
• Bitdepth, sample size, resolution, or dynamic range –
how many numbers are used to represent the value of
each sample.
Digital Audio
• Device independent – quality of audio is based on the
quality of recording and not the device on which it will
be played.
• CD-quality: 44.1 kHz, 22.05 kHz, and 11.025 kHz –
three sampling frequencies most often used in
multimedia.
• Quantization – rounding off to the nearest integer the
value of each sample. If the amplitude is greater than
the intervals available, clipping of the top and bottom
of the wave occurs. Can produce an unwanted
background hissing noise, and clipping may severely
distort the sound.
Preparing Digital Audio Files
• Fairly straightforward, analog source materials—music
or sound effects recorded on analog media such as
cassette tapes—could be digitized by recording onto
computer-readable digital media by playing sound from
one device right into your PC using digitizing software.
• Focus on two crucial aspects:
Balancing the need for sound quality against file size.
Higher quality means larger files, requiring longer
download times on the Internet and more storage
space on a CD or DVD.
Setting proper recording levels to get a good, clean
recording.
Preparing Digital Audio Files
File Size Versus Quality
• Sampling at higher rates (44.1 kHz or 22.05 kHz) more
accurately captures the high-frequency content of
sound.
• Audio resolution (8- or 16-bit) determines the accuracy
with which a sound can be digitized. More bits yields a
recording that sounds more like its original.
• Stereo recordings are more lifelike and realistic than
mono recordings. Formulas for determining size:
Monophonic recording: sampling rate * duration of
recording in seconds * (bit resolution/8) * 1.
Stereo recording: sampling rate * duration of
recording in seconds * (bit resolution/8) * 2.
(Sampling rate (in kHz)* 1000)
Preparing Digital Audio Files
Setting Proper Recording Levels
• Digital audio recording and editing software will display
digital meters to let you know how loud your sound is.
• Unlike analog meter that usually have a 0 setting
somewhere in the middle and extend up into ranges like
+5, +8, or even higher, digital meters peak out.
• To avoid distorting, do not cross over limits where the
digital meter peaks out.
• Keep peak levels between -3 and -10.
Preparing Digital Audio Files
Editing Digital Recordings
• Audacity is a free open source editing application for
Windows, Macintosh, and Linux operating systems
(http://audacity.sourceforge.net).
• Multiple Tracks – being able to edit and combine
multiple tracks (for sound effects, voice-overs, music,
etc.) and then merge the tracks and export them into a
“final mix” to a single audio file.
• Trimming – removing “dead air” or blank space from
the font of a recording and any unnecessary extra time
off the end. Accomplished by dragging the mouse
cursor over a graphic representation of your recording
and choosing a menu command such as Cut, Clear,
Erase or Silence.
Preparing Digital Audio Files
Editing Digital Recordings
• Splicing and Assembly – removing the extraneous
noises that inevitably creep into a recording. Cutting
and pasting together many shorter ones.
• Volume Adjustments – providing a consistent volume
level for multiple recordings. Use a sound editor to
normalize the assembled audio file to a particular level,
80 percent to 90 percent of maximum.
• Format Conversion – reading a format different from
that read by presentation or authoring program.
• Resampling or Downsampling – reducing the number of
samples. Saves disk space
• Fade-ins and Fade-outs – enveloping capacity for long
sections. Helps to smooth very beginning and very end
of a sound file.
Preparing Digital Audio Files
Editing Digital Recordings
• Equalization – modifying a recording’s frequency content
so that it sounds brighter or darker also called digital
equalization (EQ).
• Time Stretching – altering the length of a sound file
without changing its pitch.
• Digital Signal Processing (DSP) – processing the signal
with reverberation, multitap delay, chorus, flange, and
other special effects. Do not overdo the sound effects.
• Reversing Sound – reversing all or a portion of a digital
audio recording. Can produce a surreal, otherworldly
effect when played backward.
Making MIDI Audio
• Takes time and musical skill to work with MIDI (Musical
Instrument Digital Interface).
• You will need the following:
Sequencer software – lets you record and edit MIDI
data.
Sound synthesizer – typically built into the sound
board on PCs, but an add-on board for Macintosh).
MIDI keyboard – useful for simplifying the creation of
musical scores. Can easily edit score.
• Device dependent – quality of the playback depends
upon the end user’s MIDI device.
• General MIDI numbering system – identifies
instruments that can be synthesized.
• A production tool rather than a delivery medium. The
best way to create original music.
Audio File Formats
• A recognized methodology for organizing the digitized
sound’s data bits and bytes into data file.
• Linear Pulse Code Modulation – storage method used
for Red Book Audio data files on consumer-grade music
CDs. CD can provide up to 80 minutes of playing time,
enough for a slow-tempo rendition of Beethoven’s Ninth
Symphony. Incidentally, being able to contain
Beethoven’s Ninth is reported to have been Philip’s and
Sony’s actual size criterion during early research and
development for determining the sectors and ultimately
the physical size of the compact disc format itself.
• CD-ROM/XA (extended architecture) – format for
reading and writing CDs developed to put several
recording sessions onto a single CD-R disc.
MIDI Versus Digital Audio
• MIDI (Musical Instrument Digital Interface):
Communications standard developed in the early
1980s for electronic musical instruments and
computers.
Allows music and sound synthesizers from different
manufacturers to communicate with each other
through cables connected to the device.
Provides a protocol for passing detailed descriptions of
a musical score, such as the notes, sequences of
notes, and the instrument that will play these notes.
Not digitized sound, it is a shorthand representation of
music stored in numeric form.
A score dependent on the quality of your musical
instruments and the capabilities of your sound system.
MIDI Versus Digital Audio
• Digital Audio:
A recording that depends only on the capability of the
sound system.
The actual representation of a sound, stored in the
form of thousands of individual numbers.
The digital data represents the instantaneous
amplitude of a sound at discrete slices of time.
Not device dependent so it sounds the same every
time it is played.
Large data storage files.
Used for music CDs and MP3 files.
Advantages of MIDI
• Much more compact and the size is completely
independent of playback quality.
• Files embedded in web pages load and play quicker.
• If the MIDI sound source is of high quality, they may
sound better than digital audio files.
• You can change the length of a MIDI file (by varying its
tempo) without changing the pitch of the music or
degrading the audio quality.
• Completely editable—right down to the level of an
individual note. The smallest detail of a MIDI
composition can be manipulated.
Disadvantages of MIDI
• Because MIDI data does not represent sound but
musical instruments, playback will be accurate only
if the MIDI playback device is identical to the device
used for production.
• Cannot easily be used to play back spoken dialog,
although expensive and technically tricky digital
samplers are available.
Advantages of Digital Audio
• Consistent playback quality. There is increased
confidence that the audio track for the multimedia
project will sound as good in the end as it did in the
beginning when it was created.
• A wider selection of application software and system
support is available for both Macintosh and
Windows platforms.
• Preparation and programming required for creating
do not demand knowledge of music theory.
Choosing Between MIDI
and Digital Audio
In general, use MIDI data when:
• Digital audio won’t work because you don’t have
enough RAM, hard disk space, CPU processing power, or
bandwidth;
• You have a high-quality MIDI sound source;
• You have complete control over the machines on which
your program will be delivered, so you know that your
users will have high-quality MIDI playback hardware;
and
• You don’t need spoken dialog.
Choosing Between MIDI
and Digital Audio
In general, use digital audio when:
• You don’t have control over the playback hardware;
• You have the computing resources and bandwidth
to handle digital files; and
• You need spoken dialog.
Sound for the World Wide Web
• 2 methods for playing digital or MIDI sound on the
Web: (1) wait for the entire sound file to download to
your computer, then play it back with a helper
application; and (2) begin to play the sound file being
downloaded as soon as enough of the sound is cached
in your computer’s buffer (a place where data is stored
temporarily).
• Streaming files is dependent upon connection speed:
you must wait longer (streaming latency) before the
streamed sound begins to play for slower connections.
Adding Sound to Your Multimedia
Steps to bring an audio recording into your multimedia
project:
1. Determining the file formats that are compatible with
your multimedia authoring software and the delivery
medium(s) you will be using.
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 (such as
background music, special sound effects, and spoken
dialog). Decide where these audio events will occur in
the flow of your project. Fit the sound cues into your
storyboard, or make up a cue sheet.
Adding Sound to Your Multimedia
Steps (continued)…
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 they are timed properly with
the project’s images. This may involve repeating steps
1 through 4 until everything is in sync.
Music CDs
• ISO 10149 or Red Book (derived from the
standard’s book jacket) – international standard
which is the method for digitally encoding the highquality stereo of the consumer CD music market.
Developers of this standard claim that the digital
audio sample size and sampling rate of Red Book
Audio (16 bits at 44.1 kHz) allow accurate
reproduction of all sounds that humans can hear.
Copyright Issues
• Ownership rights are significant issues for
multimedia producers and play it safe by making
their own music from scratch in a sound studio or
with synthesizers.
• You can purchase and use digitized clip sounds with an
unlimited-use, royalty-free license.
Time for
Questions
Thanks…
References:
Books:
• Multimedia: Making It Work
By: Tay Vaughan
Web sites:
• http://www.google.com.ph