Transcript Adobe Photoshop 7.0 Design Professional

Introduction to Multimedia
Unit
7
–
Multimedia Element:
Sound
2014-15 Semester 2
Introduction to Multimedia
Unit 7: Multimedia Element: Sound
Unit Outline
• In this unit, we will learn
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Use of Sound
Guidelines for Using Sound
Basic Principles of Sound
Sound Quality
• Sample Rate
• Audio Resolution
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Digital Audio File Size
Audio Compression
Downloaded vs. Streamed
Sound Card
Digital Audio Software
Media Players
Audio File Formats
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Introduction to Multimedia
Unit 7: Multimedia Element: Sound
Introduction
• The element of sound can be important to
achieve the goals of a multimedia product.
• Sound adds another dimension.
• If used well, sound is an extremely powerful
element which can stimulate emotional
responses that would never be activated from
text and graphics alone.
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Introduction to Multimedia
Unit 7: Multimedia Element: Sound
Introduction
• Sound helps convey the intended message or
complement the purpose of multimedia
applications.
• To help ensure effectiveness, it is important to
incorporate sound files that are high quality,
appropriate, and consistent with the goals of the
multimedia product.
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Introduction to Multimedia
Unit 7: Multimedia Element: Sound
Use of Sound
• Providing controls (such as skip, pause, mute,
volume adjustment) is an effective way of
keeping users involved and motivated.
• The decision to incorporate sound into a
multimedia product should have solid reasoning
behind it.
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Introduction to Multimedia
Unit 7: Multimedia Element: Sound
Use of Sound
• Sounds are either content sounds or ambient
sounds.
• Content sounds furnish information
– Narration, dialogue are content sounds.
– Music and other sounds can be considered as content
sounds if they are parts of the topic themselves.
• Ambient sounds reinforce messages and set the
mood
– Background sounds and special effects are ambient
sounds.
– Special sound effects can reinforce or enliven a
message.
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Introduction to Multimedia
Unit 7: Multimedia Element: Sound
Guidelines for Using Sound
• Use the same style of music (if multiple sound
files are needed) to maintain a sense of unity
• Coordinate sound files with other media
elements
• Sound quality should be kept consistent
• Record at a rate and resolution that is
appropriate to the delivery mode
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Introduction to Multimedia
Unit 7: Multimedia Element: Sound
Guidelines for Using Sound
• Use the same voice for narration and voiceovers,
but different voices for different characters
• Optimize files for background music
• Use sound cues for specific events
• During voice-overs, background music should
be turned off or adjusted to a low volume such
that the spoken words can be understood
without difficulty
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Introduction to Multimedia
Unit 7: Multimedia Element: Sound
Basic Principles of Sound
• When we speak, vibrations, called sound waves,
are created.
• Sound waves have a recurring pattern or an
analog wave pattern called a waveform.
This analog wave pattern represents the volume and frequency of a sound.
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Introduction to Multimedia
Unit 7: Multimedia Element: Sound
Basic Principles of Sound
• Amplitude: Distance between the valley and the
peak of a waveform; determines volume
• Volume is measured in decibels (dB)
– Decibel (dB) is a logarithmic unit used to describe a
ratio.
– One dB is close to Just Noticeable Difference (JND)
for sound level.
• Frequency: Number of peaks that occur in one
second measured by the distance between the
peaks; determines pitch
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Introduction to Multimedia
Unit 7: Multimedia Element: Sound
Basic Principles of Sound
• Analog sound is a continuous stream of sound
waves. For sound to be included in multimedia
applications, analog sound must be converted to
digital form.
• Digitizing (or sound sampling): the process of
converting analog sound to numbers
• Digital Audio: An analog sound that has been
converted to numbers
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Introduction to Multimedia
Unit 7: Multimedia Element: Sound
Basic Principles of Sound
Sound sampling converts analog sound to digital audio.
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Introduction to Multimedia
Unit 7: Multimedia Element: Sound
Basic Principles of Sound
• During digitizing, sound samples are taken at
regular time instants.
• Time instants are discrete.
• Sound samples (the volumes of sound at time
instants) cannot be stored precisely. Instead,
only quantified values can be stored.
• The feasible quantified values are known as
quantization levels.
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Introduction to Multimedia
Unit 7: Multimedia Element: Sound
Basic Principles of Sound
• The number of quantization levels is related to
the quality of digital audio.
• If more quantization levels are allowed, the
difference between the original value and the
quantified value will be smaller and we will get a
better quality of the digital representation.
However, this would also mean a higher cost for
storage and processing of these values inside a
computer (disks of larger capacity and more
powerful CPUs are required)
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Introduction to Multimedia
Unit 7: Multimedia Element: Sound
Sound Quality
• Factors that determine the sound quality of
digital audio
– sample rate
– audio resolution
• Sample rate
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Number of sound samples taken per second
Also known as sampling rate
Measured in kilohertz (kHz),
Common values: 11 kHz, 22 kHz, 44 kHz
CD quality: 44 kHz
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Introduction to Multimedia
Unit 7: Multimedia Element: Sound
Sound Quality
• Audio resolution
– Also known as sample size or bit resolution
– Number of binary bits used to represent each sound
sample
– As the audio resolution increases, the quality of the
digital audio also improves.
– Audio resolution determines the accuracy with which
sound can be digitized.
– Common values: 8 bits, 16 bits
– CD quality: 16 bits
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Introduction to Multimedia
Unit 7: Multimedia Element: Sound
Sound Quality
Audio Resolution
Number of Quantization Levels
16-bit
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65536 possible values for the sound sample
8-bit
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256 possible values for the sound sample
4-bit
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16 possible values for the sound sample
2-bit
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4 possible values for the sound sample
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Introduction to Multimedia
Unit 7: Multimedia Element: Sound
Monophonic vs. Stereo Sound
• Monophonic sounds: flat and unrealistic when
compared to stereo sounds
• Stereo sounds: much more dynamic and lifelike
• Monophonic sound files are sometimes a more
appropriate choice where storage and transfer
time are major concerns.
• Narration and voiceovers can effectively be
saved in a monophonic format.
• Music almost always must be recorded and
saved in stereo.
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Introduction to Multimedia
Unit 7: Multimedia Element: Sound
Digital Audio File Size
File size of a digital audio recording (in bytes)
(assume that there is no compression)
* Where number of channels, either 1 for monophonic or 2 for stereo
File size of a monophonic digital audio recording (in bytes)
(assume that there is no compression)
File size of a stereo digital audio recording (in bytes)
(assume that there is no compression)
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Introduction to Multimedia
Unit 7: Multimedia Element: Sound
Audio Compression
• Similar to image compression (refer to Unit 5),
mathematical algorithms are used to reduce file
sizes.
• File size is the primary consideration when
using audio files on the Web.
• Compression is beneficial for storing and
transferring audio files.
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Introduction to Multimedia
Unit 7: Multimedia Element: Sound
Audio Compression
• Different compression schemes are available for
different file formats, and some file formats
include the compression scheme within the
format itself.
• The compression scheme applied impacts both
the quality of audio file and the file size.
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Introduction to Multimedia
Unit 7: Multimedia Element: Sound
Digital Audio File Size (Revisit)
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(Recall from Unit 5)
• Example: When a 6 MB audio file is compressed to 3 MB,
the compression ratio is (6 / 3) = 2.
File size of a digital audio recording (in bytes)
(assume that the compression ratio is CR)
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Introduction to Multimedia
Unit 7: Multimedia Element: Sound
Downloaded vs. Streamed
• Web audio: downloaded or streamed
• Downloaded audio file must be entirely saved to
the user’s computer before it can be played.
• Streaming: a more advanced process that
allows audio file to be played as it is
downloading (i.e. before the entire file is
transferred to the user’s computer)
• If we want our audio files to be streamed over
the Internet, the web-hosting service must
support streaming.
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Introduction to Multimedia
Unit 7: Multimedia Element: Sound
Downloaded vs. Streamed
• If the user’s computer receives streaming audio
data more quickly than required, the excess
data will be stored in a buffer.
• If the user’s computer receives streaming audio
data slower than required, the data stored in the
buffer will be used. If the buffer becomes empty,
the user will experience a break.
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Introduction to Multimedia
Unit 7: Multimedia Element: Sound
Downloaded vs. Streamed
• Two types of streamed audio:
– On demand
• Streamed audio is stored on a server for a long period of
time, and is available for transmission at a user’s request
– Live
• Live streams are only available at one particular time
• Example: live radio programme
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Introduction to Multimedia
Unit 7: Multimedia Element: Sound
Delivery
• To play sound on a computer system, a sound
card and speakers, or a headset are needed.
• The digital audio file is sent through a digital-toanalog converter (DAC) so that it can be heard.
• It is important to test sounds under a variety of
different conditions.
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Introduction to Multimedia
Unit 7: Multimedia Element: Sound
Sound Card
• Is an expansion board in a computer which
interfaces with the processor through slots on
the motherboard
• Can be integrated on the motherboard
• Externally it is connected to speakers for
playback of sound
• Main functions:
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Playback
Digitizing
Recording
Compressing
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Introduction to Multimedia
Unit 7: Multimedia Element: Sound
Sound Card
• Example: Creative Labs SoundBlaster
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Introduction to Multimedia
Unit 7: Multimedia Element: Sound
Sound Card
• Basic components of sound card:
– Memory banks
• for storing audio data during digitization and playback of
sound files
– DSP (Digital Signal Processor)
• gives the sound card ability to perform functions like
digital filtering, anti-aliasing, noise shaping and
compression
– DAC / ADC (Digital-to-Analog Converter, Analog-toDigital Converter)
• for digitizing analog sound and reconverting digital
sound files to analog form for playback
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Introduction to Multimedia
Unit 7: Multimedia Element: Sound
Sound Card
– Input Ports: MIC, Line In
• for feeding audio data to the sound card through a
microphone connected to it; for feeding audio data from
external CD players for recording or playback
– Output Ports: Speakers, Line Out
• for attaching speakers for playback of sound files; for
connecting to external recording devices or an external
amplifier
– MIDI Input Port
• for interfacing with an external synthesizer. Using this
connection, MIDI songs can be composed on the PC
using software and then can be sent to the sound
modules of external synthesizers for playback.
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Introduction to Multimedia
Unit 7: Multimedia Element: Sound
Digital Audio Software
• Traditional sound studio equipment is utilized to
record, mix and edit audio. The cost can be tens
of thousands of dollars.
• With sound editing
and mixing software,
audio files can be
produced for much
less money.
Sound editing software is generally a much
cheaper way to mix audio for a multimedia
application than using traditional sound
studio equipment.
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Introduction to Multimedia
Unit 7: Multimedia Element: Sound
Digital Audio Software
• Examples:
– Peak
• for Macintosh platform
– Sound Forge
• for Windows platform
– Adobe Audition
• for Windows platform
• formerly called Cool Edit
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Introduction to Multimedia
Unit 7: Multimedia Element: Sound
Digital Audio Software
• Basic sound editing operations
– Multiple tracks editing
• Edit and combine multiple tracks and then merge the
tracks and export them in a “final mix” to a single audio
file
– Trimming
• Remove “dead air” or blank space from the front of a
recording and any unnecessary extra time off the end
– Splicing and assembly
• Remove the extraneous noises that inevitably creep into
a recording
– Volume adjustments
• Provide a consistent volume level
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Introduction to Multimedia
Unit 7: Multimedia Element: Sound
Digital Audio Software
– Format conversion
• Import and save files in various formats
– Resampling or downsampling
• Increase or reduce sample rates
– Fade-ins and fade-outs
• Smooth out the very beginning and the very end of a
sound file
– Reversing sounds
• Reverse all or a portion of a digital audio recording
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Introduction to Multimedia
Unit 7: Multimedia Element: Sound
Media Players
• Popular media players:
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Windows Media Player
QuickTime Player
RealPlayer
iTunes
• Media players should:
– be equipped to open and display most popular audio
file formats
– possess the ability to play live
streaming audio
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Introduction to Multimedia
Unit 7: Multimedia Element: Sound
Audio File Formats
• MP3 (MPEG - Audio Layer 3)
– Open standard technology
– Uses file compression to create near-CD quality audio
files
• WAV (Waveform format)
– for Windows platform
• Real formats (RA, RAM, RM)
– for streaming audio
• WMA (Windows Media Audio)
– Developed by Microsoft
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Introduction to Multimedia
Unit 7: Multimedia Element: Sound
Audio File Formats
• ASF (Advanced Systems Format)
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Formerly known as Advanced Streaming Format
Mircosoft’s proprietary format for streaming
Stores audio and video information
Specially designed to run on networks
Content is delivered to users as continuous flow of
data; little waiting time will be experienced before
playback begins
• AIFF or AIF (Audio Interchange File Format)
– Macintosh waveform format
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Introduction to Multimedia
Unit 7: Multimedia Element: Sound
Audio File Formats
• MIDI (Musical Instrument Digital Interface):
– Internationally accepted file format for storing MIDI
data
– Provides instructions on how to replay music; does not
record the waveform (MIDI data is not digital audio)
– Files of MIDI format are often smaller than those of
most other audio file formats
– If spoken dialog is needed, digital audio should be
used instead
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Introduction to Multimedia
Unit 7: Multimedia Element: Sound
Reference
• Part of this slide set is prepared or/and extracted
from the following book:
– Multimedia For The Web Revealed, Calleen Coorough
& Jim Shuman, Thomson Learning, 2006, ISBN:14188-3953-1
• This set of slides is for teaching purpose only.
• Self-study slide(s) is / are within the scope of the
final examination.
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