Transcript CITB 123: MULTIMEDIA TECHNOLOGY

CITB 123: MULTIMEDIA
TECHNOLOGY
CHAPTER SIX
MBB: SOUND
Prepared by:
Noor Fardela Zainal Abidin
© UNITEN 2004/2005
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Introduction to 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).
 Sound travels as waves at 750 mph (at sea level)
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Why is sound important in
Multimedia?
 To reinforce message or theme
 To set the mood
 To catch the interest of the audience
 To alert the audience
 To include narration: effective for training
and educational application
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Types of Sound
 2 types of sound in multimedia

Music
Background
 Attention grabber
 etc..

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Speech
Narration
 Instruction
 etc..

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Sound Consideration
 While sound (music or narration) can be very
useful, most of the time, they can be irritating as
well.
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Use appropriate music to reflect the mood or theme.
Give the users choice of turning off/on the sound.
In cases where the content of a page depends on
sound (speech), consider providing transcript as the
alternative. (for deaf people, non-multimedia pc)
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Type of Audio for Multimedia
Application
 Digital Audio
 MIDI Audio (Musical Instruments Digital
Interface)
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Digital Audio
 Digital audio is a representation of the original
sound.
 Digital audio data is the actual representation of
sound, stored in the form of samples.
 Samples represent the amplitude (or loudness) of
sound at a discrete point in time.
 Quality of digital recording depends on the
sampling rate, (or frequency) that is, the number of
samples taken per second.
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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).
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Preparing Digital Audio
Digital Audio
 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
 Note
The sampling rate determines the frequency
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Preparing Digital Audio
 To calculate file size in bytes:
 Question:
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Given a 16 bit CD-quality musical piece to be sampled
using 44.1KHz (sampling rate per second) for 10
minutes; what is the size of the file in mono and stereo?
 Answer:
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44.1 x 103 x 16 bit x (10 x 60) / 8 (bits) = 52.92MBytes
For stereo (left/right) channel, the amount is doubled:
52.92MBytes x 2 = 105.84MBytes
 That’s why we need COMPRESSION!
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Preparing Digital Audio
1. Balance file sizes and quality
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Audio resolution determine the accuracy with
which a sound can be digitized i.e. how
similar the regenerated sound to the original
sound.
High quality sound audio requires high
sampling rate and size, resulting in large file.
High quality sound requires large storage.
Choose between stereo or mono recording
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Preparing Digital Audio
2. Setting proper recording level (loudness)
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Watch the meter in the recording device or
software carefully to ensure the level of
loudness are not too high or too low
Levels that are too high create distortion
(sound alteration e.g. unpleasant crackling)
Levels that are too low cause the music to be
too soft and overpower by the sound of the
recording process itself.
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Preparing Digital Audio
3. Editing the recording
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Trimming : removing blank space at the
beginning or at the end of the recorded audio.
Splice: remove unnecessary noise (touch up)
Assembly: longer recorded audio can be build by
cutting and pasting together a few shorter ones.
Convert to another audio format
Macintosh : SND and AIF files format
 Windows : WAV files format
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Preparing Digital Audio
3. Editing the recording
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Resampling or downsample: resample recorded
audio file to a lower audio resolution. e.g. resample /
downsample a 16 bit recorded sound to 8 bit.
Fade-in and fade-out: smooth out the very beginning
and the very end of the sound file.
Time stretching: alter the length of the recorded
sound
Digital Signal Processing (DSP): add special effects
to the recorded sound.
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MIDI Audio
 What is MIDI? MIDI is an acronym for
Musical Instruments Digital Interface
 Definition of MIDI: a protocol that enables
computers, synthesizers, keyboards, and
other musical devices to communicate with
each other. It is a set of instructions how a
computer should play musical instruments.
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MIDI Audio
 MIDI was developed in the 1980s as a standard
communications protocol between electronic musical
instruments and computer
 MIDI file is not a digitized sound, it is the shorthand
representation of music stored in numeric form (binary)
 MIDI file contains instructional data (notes, sequences of
notes, which instruments etc.) to other devices on how to
generate an appropriate sound, it does not have the actual
audio data, just the instruction to the instrument or sound
card on how to reproduce it.
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MIDI Audio
 Offer opportunity for developers to compose their
own music.
 MIDI files are much more smaller than digital
audio files, thus,

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It requires less storage space.
Suitable to be used with web page.
 Inconsistency in playback quality

Playback will only be accurate if the MIDI playback
device is identical to the device used for production.
 Not suitable for spoken dialogue
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Preparing MIDI Audio
You need:
 Some musical talent or hire MIDI artists.
 MIDI instruments (e.g. electronic keyboard)
 MIDI Sequencer software:
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allows you to record, edit and save music
generated by MIDI instruments.
 Computer Sound Hardware
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Preparing MIDI Audio
 MIDI Sequencer
Software
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Preparing MIDI Audio
 Sound Synthesizer:
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Is needed to translate information generated by the MIDI
devices into sound (music).
Typically built into the sound board on PC, but as an
add-on board or peripheral for the Macintosh
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Preparing MIDI Audio
MIDI Instruments
Computer with MIDI
Sound Board
Synthesizer
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Preparing MIDI Audio
 MIDI can synthesize the sounds of over a
hundreds different instruments.
 How realistic the instruments sound is
greatly affected by the hardware it is played
on.
 Each instrument is identified by a numeric
General MIDI Instrument Sound code
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MIDI VS Digital Audio
 Use MIDI data in the following
circumstances
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You only have small storage space, RAM,
CPU processing power or bandwidth.
You have high quality MIDI sound source.
You have complete control over the playback
hardware.
You do not need spoken dialogue
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MIDI VS Digital Audio
 Use digital audio in the following
circumstances
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You do not have control over the playback
hardware
You have the computing resources and
bandwidth to handle digital files.
You need spoken dialogue.
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Adding sound to Multimedia
 Before adding sound to your multimedia
project, decide on:
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What kind of sound is needed
When and where to use audio
Decide whether you want to use MIDI or digital
Acquire the source material
Edit the audio to suit your project
Test the sound
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Copyright issues
 Secure rights for all material you use
 Look for collections of royalty-free audio
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Reference
 Vaughan Tay, Multimedia: Making It work.
6th Edition. McGraw Hill
 Ibrahim Nazrita, Notes: Multimedia Design,
UNITEN. 2002
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