lec 5 Sound in multimedia

8/7/2019 lec 5 Sound in multimedia

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Multimedia System:-

Sound


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Multimedia System There is no clear definition of the term

"Multimedia System".

Common characteristics of a Multimedia System Digital

Interactive

Networking

Integration of text, graphics, sound, image, and video


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Digital MediaAnalog Data

The signals, which we send each other to

communicate, are data. Our daily datahave many forms: sound, letters, numbers,and other characters (handwritten orprinted), photos, graphics, film. All this

data is in its nature analog, which meansthat it varies in type.


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Digital Data

A digital system is an electronic unit. Therefore,

it can only deal with data, which are associatedwith electricity. That is accomplished using

electric switches, which are either off or on. It

can be illustrated with regular household

switches. If the switch is off, it reads numeral 0.If it is on, it is read as numeral 1.


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Bits

Each 0 or 1 is called a bit. Bit is an abbreviation of the

expression BInary digit, which is derived from the binary

number system.

Digital Media

0 1 bit

1 1 bit

0110 4 bit

01101011 8 bit

Table 1.1 Example of Bits


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Binary Number System

The binary number system is made up of digits.

Compare with decimal system (10 digit system),

decimal system uses digits 0 through 9, the binarysystem only uses digits 0 and 1.

Digital Media

Table 1.2 Decimal System and Binary System

Number in Decimal System Representation in Binary Number System

0 0

2 10

3 11

8 1000


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Units

1 byte = 8 bits

1 kilobytes(kB) = 1024 bytes

1 megabytes(MB) = 1000 kB = 1024000 bytes

Digital Media


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Digital MediaExamples of storage media

Hard disk, MO, Compact Disc

Pros and Cons of Digital Data

Pros: Digital can reproduce, transmit, or copy

without introducing loss in quality.

Cons: Consume a lot more bandwidth during

transmission than analog signal.


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Data Types in MM system

Text Data

ASCII stands for American Standard Code for

Information Interchange. Computers can only

understand numbers, so an ASCII code is the

numerical representation of a character.


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Text Data

Figure 2.1 ASCII table and description (copyright: www.asciitable.com)


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Text DataASCII uses 7 bits to represent a character. As a result only 127

characters are defined as standard ASCII characters. Characters

128-255 are called extended ASCII characters (Figure 2.2).

Figure 2.2 Extended ASCII codes (copyright: www.asciitable.com)


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Text Data

EBCDIC

EBCDIC (Extended Binary Coded DecimalInterchange Code) is a character set used on early

IBM computers. EBCDIC was first introduced in 1965,

it was the new character-coding scheme came with

IBM System 360 series. EBCDIC uses 8 bits to

represent a character.


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Text Data

UNICODE

The Unicode character uses 16 bits to represent acharacter, thus more than 65000 characters can be

represented. While 65000 characters are sufficient for

encoding most of the many thousands of characters

used in major languages of the world.


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Sound Data

Sound Data

A typical compact disc can hold up to 74 minutes of 16bit, 44.1 kHz audio that is uncompressed about 650

megabytes.


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Sound DataTable 2.1 shows how the size of a file is affected by the sampling

rate and bit length. The file is a one-minute sound clip, recorded

and saved in various forms in the Microsoft Windows WAV file

format.Quality Sampling Rate Resolution File Size

CD 44 kHz 16 bit Stereo 10.3 MB

44 kHz 8 bit Stereo 5.18 MB

FM Radio 22 kHz 16 bit Stereo 5.18 MB


AM Radio11 kHz 16 bit Stereo 2.59 MB


Table 2.1 Variation of file size and sampling rate (60 seconds audio clip in MS WAV format)


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Image Data

Image Data

Images, or pictures, are two-dimensional arrays ofdata called bitmaps, with each element is called pixel.


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Image Data

Units

Dpi - Dots Per Inch

Bit Depth - The number of bits used to hold a pixel.

Also called color depth and pixel depth, the bit depthdetermines the number of colors that can be displayed

at one time.Color Depth Number of Colors

4 bits 16

8 bits 256

16 bits 65,536

24 bits 16,777,216

Table 2.2 Color Depths


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Video Data

Video Data

Video, or moving images, is a sequence of images.

To create a sense of continuity, video must be

played at a rate of at least 25 frames per second (fps).


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Quality of Service (QoS)

Modern multimedia systems feature networking.

Multimedia data over the network consists the

following characteristics:

Time Critical

Synchronization

Order of Arrival

Tolerance ofError


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Quality of Service (QoS)

QoS can be parameterized from an end-to-end point

of view:

Bandwidth Required

Delay

Delay Jitter (Variation of a delay)

Reliability (Error rate)


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Lossless & Lossy Compression

Lossless Compression

The original data obtained from lossless compression

can be recovered from its compressed datae.g. Huffman Coding

Lossy Compression

Compressed data of lossy compression cannot berecovered to the original data.

e.g. JPEG, MPEG


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Human Auditory System

Sound Localization

The basic 3 types of information to localize a soundsource received at the ears:

Interaural intensity difference

Interrarural phase difference

Interraural time difference


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SoundLocalization

When you listen a single speaker, your ears receive

both direct sound from each speaker and multiple

reflections contributed by the room's surfaces and

furnishings (Figure 5.1).

Figure 5.1 Reflection of Sound (copyright: Dolby Laboratories, Inc)


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Sound Localization

One of the most advanced technologies related to

sound localization is Dolby Headphone. Dolby

Headphone emulates multispeaker surround systems,

such as Dolby Digital 5.1-channel.

Figure 5.2 (a)Dolby Digital 5.1-channel (b)Dolby Headphone (c)Dolby Headphone Stereo Symbol

(copyright: Dolby Laboratories, Inc)

(a) (b) (c)


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Sound Localization

Figure 5.3

First portable audio product equipped with

Dolby Headphone technology released in

August 2001


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Human Vision System

Figure 6.1 Mach Band Effect

Brightness and Mach Band

The left side of each bar appears to be lighter than

the right side. While appear to be darker on the right.

This is called the Mach band Effect.


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Human Vision System

Figure 6.2 Spatial frequency response of human eye

Spatial Frequency Analysis

Human eye response is the best at the middle and

falls off at both ends (Figure 6.2).

Highest responseIncreasingamplitude

Increasing frequency


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Human Vision System

ColorVision

The human eye can respond to light of wavelength

400nm to 700nm, and the response peaks at around

550nm, which is corresponding to green. There are 3 types of cones, which respond to red, green,

and blue.

The mixing of three primary colors red, green, and blue

to form other colors is called the RGB color model. Other color model such as CMYK, is commonly used in

the printing industry.


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Summary

Common characteristics of multimedia systems:

digital, interactive, distributed, and involving a wide

range of data types, such as video and audio.

QoS as an alternative to best effort approach in

networking.

Characteristics of Human Auditory and Vision are

presented.

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lec 5 Sound in multimedia