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Sound
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Introduction to Sound
Vibrations in the air create waves of pressure that areperceived as sound.
Sound comprises the spoken word, voices, music and evennoise.
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 measuredin decibels (dB).
Something vibrates
in the air Waves of pressure
Ear drums will translate
these changes in wave
Forms as sound
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Introduction to Sound
A pleasant sound has a regular wave pattern. Thepattern is repeated over and over.
But the waves of noise are irregular. They do not have a repeated
pattern.
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Multimedia System Sound
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.
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Characteristic of SoundWaves
Sound is described in terms of two characteristics:
Frequency (or pitch)
Amplitude(or loudness)
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Frequency
Frequencyis a measure of how many cycles occur in one second. This ismeasured in Hertz(abbreviation Hz) and directly corresponds to thepitch
of a sound.
The more frequent vibration occurs the higher the pitch of the sound.
Optimally, people can hear from 20 Hz to 20,000Hz (20 kHz)
Sounds below 20 Hz are infrasonic
sounds above 20 kHz are ultrasonic.
Low pitch High pitch
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Amplitude
Amplitudeis the maximum displacementof a wave from an
equilibrium position.
The louder a sound, the more energy it has. This means loud
sounds have a large amplitude.
The amplitude relates to how loud a sound is.
Low amplitude High Amplitude
Quiet Loud
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Characteristic of SoundWaves
distance
along wave
Cycle
Time for one cycle
Amplitude wavelength
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Audio Recording Software
MACINTOSH WINDOWS
Sound Recorders for Windows Both Macintosh and Windows PC platform have the default sound. This basic application could:
Record our own sounds Edit & mix *.wav files
Simple Splicing and assembly Increase volume & speed of *.wav files Reverse the sound.Add Echo effects Some XP Version also provide wav to mp3 conversion.
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Basic Sound Recorder
Sound conversion
Basic Effects
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Capture & Playback of Digital Audio
Air pressure
variations
Captured via
microphone
Air pressure
variations
ADC
Signal is
converted into
binary
(discrete form)0101001101
0110101111
Analogueto DigitalConverter
DAC
Convert
s backinto
voltage
Digital toAnalogueConverter
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Recording Audio Files
Recording Audio Files on the pc
Uses either:
i. Microphone
connect microphone to the microphone port and record using
sound recorder
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Recording Audio Files
ii. CD-ROM Drive
Move music files from CD to hard drive or;
Play the cd and then record using the sound recorder.
iii. Line-in
pressing play on the audio source, which is connected to the
computers audio line-in socket. Record using the sound recorder.
Audio cable
Line in porton the pc
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Analogue audio The name for an electronic signal that carries its information of sound
as continuous fluctuating voltage value. Stored in non digital tape or audio tape recording of sound.
Digitizing the process of converting an analog signal to a digital one.
A sound is recorded by making a measurement of the amplitudeofthe sound at regular intervals which are defined by the "sampling rate(frequent of sample point taken).
The process of taking the measurement is called "sampling" and eachmeasurement is called a "sample point".
Analogue to Digital Audio
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Digital Audio
Digital audio - data are stored in the form of samples point.
Samples represent the amplitude (or loudness) of sound at a discrete
point in time.
Quality of digital recording depends on thesampling rate, the number
of samples point taken per second (Hz).
High Sampling Rate
Low Sampling Rate
Samples stored in digital
form
waveform
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Digital Sampling
1 second
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Digital Sampling
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Digital Audio
There are three sampling frequencies most often used in multimedia are
44.1 kHz, 22.05 kHz and 11.025 kHz.
The higher the sampling rate, the more the measurementsare
taken (better quality).
The lower the sampling rate, the lesser the measurementsare
taken (low quality).
The number of bits used to describe the amplitude of sound wave when
sampled, determines the sample size.
Low Sampling RateHigh Sampling Rate
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Digital Audio
Quality factorsfor digital audio file :1. Sampling Rate
2. Sample Size (resolution)
the number of bits used to record the value of a sample in a
digitized signal.
Sampling Rate Sample size
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Digital Audio
Other than that, it also depends on:
The quality of original audio source.
The quality of capture device & supporting hardware.
The characteristics used for capture.
The capability of the playback environment.
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Digital Audio
Crucial aspects of preparing digital audio files are:
Balancing the need for sound quality against available RAM
and hard disk resource.
Setting appropriate recording levels to get a high-quality and
clean recording.
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Digital Audio
Audio resolution determines the accuracy with which sound
can be digitized.
Size of a monophonic digital recording = sampling rate x
(bit resolution/8) x 1.
Size of stereo recording = sampling rate x duration of
recording in secondsx (bit resolution/8) x 2.
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Digital Audio
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.
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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Digital Audio - Software
More advanced Digital audio editing software: One of the most powerful and professional PC-based packages is a
tool called Sound Forge
http://www.sonicfoundry.com/
Others audio editing software:
COOL Edit Pro
Gold Wave
PROSONIQ SonicWORX
Samplitude Studio
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MIDI Audio
Musical Instrument Digital Interface (MIDI)
Before there was a wide use of mp3 and high bandwidth network,
MIDI format audio is popular when an audio is required to be put on a
website.
Provides a standard and efficient, means of conveying musical
performance information as electronic data.
MIDI is a shorthand representation of music stored in numeric form.
It is in the form of music score and not samples or recording. It is not
digitized sound.
Purposely for music
A sequencer software and sound synthesizer is required in order to
create MIDI scores.
MIDI is device dependent.
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MIDI Audio
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.
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Recording MIDI Files
Recording MIDI Files
MIDI files can be generated:
by recording the MIDI data using MIDI instrument (electronic
keyboard) as it is played.
by using a MIDI sequencer software application to record and edit
(cut, paste, delete, insert).
MIDI keyboard
MIDI sequencer
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Audio File Formats
MIDI
*.MID, *.KAR, *.MIDI, *.SMF
AUDIO DIGITAL
WINDOWS *.WAV
MACINTOSH
*.AIFF
UNIX *.AU
REALAUDIO *.RA
MPEG3 *.MP3
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MIDI Versus Digital Audio
MIDI is analogous to structured or vector graphics, while
digitized audio is analogous to bitmapped images.
MIDI is device dependent while digitized audio is device
independent.
MIDI files are much smaller than digitized audio.
MIDI files sound better than digital audio files when played
on a high-quality MIDI device.
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With MIDI, it is difficult to playback spoken dialog, while
digitized audio can do so with ease.
MIDI does not have consistent playback quality while digital
audio provides consistent playback quality.
One requires knowledge of music theory in order to run
MIDI, while digital audio does not have this requirement.
MIDI Versus Digital Audio
Adding Sound to Multimedia
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Adding Sound to MultimediaProject
File formats compatible with multimedia authoring software
being used along with delivery mediums, must be
determined.
Sound playback capabilities offered by end users system
must be studied.
Adding Sound to Multimedia
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Adding Sound to MultimediaProject
The type of sound, whether background music, special
sound effects, or spoken dialog, must be decided.
Digital audio or MIDI data should be selected on the basis
of the location and time of use.
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Advantages & Disadvantages of UsingAudio
Sound adds life to any multimedia application and plays important
role in effective marketing presentations.
Advantages
Ensure important information is noticed.
Add interest.
Can communicate more directly than other media.
Disadvantages
Easily overused.
Requires special equipment for quality production.
Not as memorable as visual media.
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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.
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Production Tips
It is vital to maintain a high-quality database that stores
the original sound material.
Sound and image synchronization must be tested at regular
intervals.
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Production Tips
The speed at which most animations and computer-based
videos play, depends on the users CPU.
Sounds RAM requirements as well as the users playback
setup must be evaluated.
Copyrighted material should not be recorded or used
without securing appropriate rights from owner or
publisher.
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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.
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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 files sound better than digital audio files when played
on high-quality MIDI device.