Transcript dvd converter

BITM 1113
Introduction to Digital Audio
Chapter 6
Sound & Digital Audio
Principles of Sound and Audio
Common Media Term & Concepts
Introduction

Sound is perhaps the most sensuous element
of multimedia.
 It is meaningful “speech” in any language,
from whisper to a scream
 How you use the power of sound can make
the difference between an ordinary
multimedia presentation and a professionally
spectacular one
 Misuse of sound, however, can wreck your
project.
2
All sound waves are analog in nature, made of an
unbroken line without individually distinguishable
pieces or components forming the sound wave
This contrasts to digital signals, which break the
wave into many individual components that
approximate or mimic the shape of the wave
All other media are primarily visual, while sound is
perceived through the different sense of hearing
It is a complex mixture of physical and psychological
factors which is difficult to model accurately
3
Sound wave




The pattern of sound wave, usually displayed as a
two-dimensional graph of pressure or amplitude
against time
For periodic waveforms, a single cycle or period
defines the waveform.
Also called sound pressure function, particularly
when represented digitally
Digital sound is a sound that has been converted to
or created (synthesized) in a discrete form (numeric
values) suitable for storage and processing in a
computer
4
Principles of Sound



Sound can be describes as oscillations (ayunan,
buaian, getaran) of air pressure that stimulate the
eardrum to the auditory nerves and the brain.
The oscillations must occur in a range of frequencies
and amplitudes.
The hearing range of the average person is
approximately 20Hz to 17KHz
5
Sound waves in air


A single-frequency sound wave traveling through air
will cause a pressure variation in the air
The air motion which accompanies the passage of
the sound wave will be back and forth in the direction
of the propagation of the sound
6

The idea of tuning fork resemble those created by a
pendulum
 Our ears are the main receptors for sound
 The eardrum forms a membrane that is connected to
a body of liquid and is sensitive to pressure changes
within certain wavelengths
 The pressure changes result in hydraulic action that
is converted into the electrical signals ultimately
interpreted by the brain as sound.
7
• Sound wave’s amplitude
• Sound wave’s frequency
= sound’s intensity
= the length of time taken for the
wave to complete one entire cycle
Measured in unit Hertz (a cycle per second)
1000 Hertz = 1 KHz = 1000 cycle per second
8
Frequency





The reciprocal value of the period; it represents the
number of periods in a second and is measured in
hertz (Hz) stand for a cycles per second (cps).
[ 1 HZ = 1 cycle per second ]
Determined by the length of time it takes the waves
to complete one entire cycle.
One cycle is when the wave goes up, down through
the line and back up again to the starting point
In Multimedia systems - make use of sound only
within the frequency range of human hearing - audio
(acoustic signals) - speech, music and noise (range
between 20Hz to 20kHz).
Every musical note has a related hertz value
9
Amplitude




The sound’s intensity or loudness
Measure of the displacement of the air pressure
wave from its mean or rest position
It has to do with the distance above and below the
centerline of the sound wave
The center line is the horizontal line in the drawings
below, it is zero degrees
10
Psychology of Hearing




The properties of frequency and amplitude have
corresponding concepts in auditory perception: pitch
and loudness
Pitch: Pitch of sound depends upon the frequency of
sound. The greater the frequency, the higher is the
pitch and vice versa.
It is the pitch of sounds that enable us to
distinguished b/w a sound of man and woman or man
and dog.
Etc. sound of a woman is shrill due to high pitch.
Sound of a dog is grave due to low pitch and low
frequency.
11
Pitch




The subjective impression of frequency, in the same
sense that loudness is the subjective sense of the
amplitude of a sound
The perceived pitch of a sound is just the ear's
response to frequency
Pitch is a psycho acoustic variable, and the degree of
sensitivity shown to it varies widely with people
The pitch of a tone or note allows it to be placed in a
musical scale; thus notes of a scale are often called
pitches, and given names (A, B, C, C#, doh, re, mi,
etc.)
12




Loudness: Corresponds
roughly to the amplitude of
the note.
The perceived loudness of a
sound depends on both the
frequency and amplitude of
the physical stimulus.
Loudness is measured in
decibels (dB)
The smallest audible sound
is 0dB. A sound 10 times
more powerful is 10dB. Here
are some common sounds
and their decibel ratings:
Decibel
DESCRIPTION
140 dB A gunshot or fire cracker
120 dB A rock concert or a jet engine
110 dB A car horn
90 dB A lawnmower
60 dB Normal conversation
15 dB A whisper
0 dB Near total silence
13
Loudness

Human ears measure the distance the ear drum
moves when we hear a sound. The message is sent
to the brain
 The brain translates the amplitude into the loudness
of the sound
 Loud sounds have a large amplitude. They make the
ear drum vibrate very far
 Soft sounds have a small amplitude. They vibrate the
ear drum very little
 If the vibration is too small or too large, a person
cannot hear the sound
14
Digital Audio




The most common form of digital audio is the
compact disc (CD)
Digitizing an analog waveform involves breaking it up
into many small pieces that can later be lined up
together to form a close approximation of the original,
continuous signal
The more samples that are taken, the more pieces
are used to recreate the signal resulting in a higher
resolution signal
Digital audio is high-quality signals that suffer from
very little distortion and noise compared to analog
signals
15
Analog to Digital Converter
(ADC)



Electronic equipment used to change or convert an
analog (waveform style) signal into a digital signal
(made up of 1s and 0s)
The job of the analog-to-digital converter is to take
the waveform (the analog signal) and split it up into
the thousands of tiny "stairs" which simulate the wave
Analog signals are converted to digital signals for a
variety of reasons including to improve processing
power (the ability to manipulate the signals), to
encode analog signals for later playback through a
digital medium (such as a CD or DVD) etc.
16
Why is it important to change
from analog to digital?

Computer is in digital format
 To get clearer, precise audio without noise
 Noise can be cut / reduce by using digital. (ability to
edit)
 Quality of data when transmitted – especially for long
distance transmission.
17
Sampling rate
 Describes how often samples are taken
 Every nth fraction of a second, a sample of sound is
taken and stored as digital information in bits and
bytes
 Three sampling frequencies most often used in
multimedia are CD quality 44.1 kHz, 22.05 kHz and
11.025 kHz.
Sampling size
 The amount of information stored about each sample.
 The more often you take a sample and the more data
you store about the sample, the finer the resolution
and quality of the captured sound when it is played
back.
 Sample sizes are either 8 bits or 16 bits.
18
Quantization
 The process of converting the sample amplitude to
bits of data
 Value of each sample is rounded off to the nearest
integer
 It can produce an unwanted background hissing
sound
Clipping
 If the amplitude is greater than the intervals available,
clipping of the top and bottom of the wave occurs.
 Clipping may severely distort the sound.
19
Digital to Analog Converter
(DAC)



Electronic device that decodes digital data (ones and
zeroes) into an analog waveform electrical signal
Digital signals from formats such as CDs and DVDs
are converted from their digital form into an analog
form in order for the amplifier and speaker to recreate
sound
Most digital playback devices (CD, DVD, laserdisc,
etc.) include a digital-to-analog converter
20
Editing Digitized Sound
• A number of software application are designed
especially for digital sound editing and modification
• Software that can be used to edit digital sound :







Sound Edit
SoundForge
Adobe Audition
Real Audio Encoder
Cybersound Sound FX
Camps
MidiScan
Webtracks
21
File Size versus Quality






Sampling rate determines the frequency makeup of
the recording
Sampling at higher rates more accurately captures
the high frequency content of your sound
Using more bits produces a recording that sounds
more like the its original.
Stereo recordings are more lifelike and realistic
because human beings have two ears.
Mono recordings are fine but tend to sound a bit “flat”
and uninteresting when compared with stereo
recording.
Stereo sound files require twice as much storage
space as mono files for the same length of time.
22
Sound files can be edited in a large number of ways :• Amplitude adjusted
• Echo effect can be added
• Pitch can be shifted
• Various filters can be applied
• Softening / Sharpening the quality of the sound
• Trimming / combining and rearranging clips
Format
File Type
File extension
: WAVE (Waveform Audio File)
: .wav
WAVE is a proprietary Standard originally developed by
Microsoft and IBM as part of the Resource Interchange
File Format (RIFF) for
Window 3.1.
23
Common File Types Used for Digitized
Sounds
•.aif
•.au
•.ram
•.mp3
•.mid/midi
24
Adding Sound to Your Multimedia Project
1.
2.
3.
4.
5.
6.
Decide what kind of sound is needed (such as background
music, special sound effects and voice over.). 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
Decide where & when you want to use either digital audio or
MIDI data
Acquire source material by creating it from scratch or
purchasing it. (Be careful of copyright issues)
Edit the sounds to fit your project
Test the sound to be sure they are timed properly with the
project’s images.
25

End of Lecture
26