Digital Audio Media Type

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Multimedia Applications

Multimedia Requirements

Basics of Digital Audio Media

Sound Categories

Sampling

Quantization

Audio Representation Standards◦ Wav

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Definitions:◦ Data: is information that may be valuable for an

end-user

◦ Media: tools used to store and deliver information or data

◦ Multimedia: communications that include multiple forms of information

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Point of Sale

Point of Information

Training

Learning

Entertainment

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Using multimedia data, the user is presented the various models available from the vendor

This can be a graphical demonstration of how the product actually works.

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2009 TOYOTA LANDCRUISER UZJ200R SAHARA (4X4)

Price: $91,990

Kilometers: 34993

Body: Wagon

Color: Pearl White

Transmission: Automatic

Engine Size: 4.7 Litres

No of Seats: 8

Fuel Type: Petrol - Unlead

Extras/Features:

17 Inch Alloy Wheels Air Con + Climate Control Multi Zone Alarm System/Remote Anti Theft Anti-Lock Braking Brake Assist CD With 6 CD Stacker Central

Interactive multimedia information systems are being used in museums, hotels, university campuses, companies, etc.

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Visual training with the help of images, animation, video and other type of multimedia is proven to be more effective.

Multiple choice exams after short video clips can lead the user through the training system.

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A successful learning system should have features for the user to explore the information.

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Entertainment is one of the important areas for multimedia applications.

Computer games are becoming widespread by simulating the real game environments.

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Multimedia data is used from a distance using computer networks.

The Internet is a public network that can be used for multimedia transmission.

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The Internet is a large network interconnecting local networks.

The Internet has a heterogeneous structure.

The Internet is a best-effort network.

The Internet does not guarantee a fixed data rate over a connection.

Multimedia data should adapt itself with network data rate changes.

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A Multimedia System is a system capable of: ◦ Processing multimedia data,

◦ Storing multimedia data,

◦ Generation and manipulation of multimedia data.

A Multimedia system has four basic features:

◦ Multimedia systems must be computer controlled.

◦ Multimedia systems are integrated.

◦ The information they handle must be represented digitally.

◦ The interface to the final presentation of media is usually interactive.

The multimedia systems should:◦ Process large amount of data

◦ The should be real time in many cases

◦ The should be able to combine different media

Multimedia data can be used as:◦ Streaming data

Data (audio, video, etc) is presented to the end-user only once (without being saved to a file).

◦ Downloadable

Data is downloaded to a file and presented to the end-user repeatedly.

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Assume a video with:◦ 25 frames per second

◦ 600 rows

◦ 800 columns

◦ 3 bytes for each pixel

The video needs 25*600*800*3 bytes per second (36 MB )

One hour video will be 129 GB

Conclusion: Compression is necessary

Audio Media Type

What is Sound?Sound is the brain's interpretation of electrical impulses being sent by the inner ear through the nervous system.

Audio is sound within the acoustic range available to humans.

An audio frequency (AF) is an alternating signal within the 20 to 20,000 hertz (cycles per second) range.

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Content Sound

Content sound provides information to audiences, for example, dialogs in movies or

theater.

Ambient Sound

Ambient sound consists of an array of background and sound effects.

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Narration: Narration provides information about an animation that is playing on the screen.

Testimonials: These could be auditory or video sound tracks used in presentations or movies.

Voice-overs: These are used for short instructions, for example, to navigate the multimedia application.

Music: Music may be used to communicate (as in a song).

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Message reinforcement: The background sounds you hear in real life, such as the crowds at a ball game, can be used to reinforce the message that you wish to communicate.

Background music: Set the mood for the audience to receive and process information by starting and ending a presentation with music.

Sound effects: Sound effects are used in presentations to liven up the mood and add effects to your presentations, such as sound attached to bulleted lists.

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Sound waves are disturbances in the air (or other mediums of transmission). The sound waves consist of compressions and rarefactions.

The amplitude measures the relative loudness of the sound, which is the distance between a valley and a crest.

The amplitude determines the volume of the sound.

The unit of measurement of volume is a decibel.

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Source Intensity Level

Threshold of Hearing (TOH) 0 dB

Rustling Leaves 10 dB

Whisper 20 dB

Normal Conversation 60 dB

Busy Street Traffic 70 dB

Vacuum Cleaner 80 dB

Large Orchestra 98 dB

Walkman at Maximum Level 100 dB

Front Rows of Rock Concert 110 dB

Threshold of Pain 130 dB

Military Jet Takeoff 140 dB

Instant Perforation of Eardrum 160 dB

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Frequency : The difference in time between the formation of two crests is termed period.

The number of peaks that occur in one second is the frequency.

Another term associated with frequency is pitch. If an object oscillates rapidly, it creates a "high-pitched" sound (treble).

A low-frequency sound on the other hand is produced by an object that vibrates slowly, such as the thicker strings of a piano or guitar (bass).

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Wavelength: Wavelength is the distance from the midpoint of one crest to the midpoint of the next crest.

Wavelength is represented by the symbol λ

Bandwidth: Bandwidth is defined as the difference between the highest and the lowest frequency contained in a signal.

A signal which spans the range of 200-3200 Hz has a bandwidth (BW) of:

BW= 3200-200 = 3000 Hz

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Few objects produce sound of a single frequency. Most musical instruments, for example, generate multiple frequencies for each note.

The combinations of frequencies generated by an instrument are known as the timbre.

A timbre consists of a fundamental or main frequency and other minor frequencies known as overtones or harmonics.

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Explain why a "note" (say, Middle C) played on a piano sounds different from the same "note“ played on a saxophone.

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The velocity of sound may be found directly by measuring the time required for the waves to travel a measured distance.

The velocity varies greatly with the medium through which it travels.

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Audio signal is an analog signal

Computers store digital signal

To convert analog signal into digital signal we have to do sampling

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Sample values can be in a large range and include real numbers.

To store sample values with less number of bits quantization is used.

In quantization the values in a range are mapped to a single number

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20,000 Hz sound, sampled at 40,000 sample/second

Quantization level: 256 (8 bits)

40,000 * 1 bytes /sec data

With 65,536 (16 bits) quantization levels, data size will be 40,000 * 2 = 80,000 bytes/second

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Fidelity is defined as the closeness of the recorded version to the original sound. In the case of digital speech, it depends upon the number of bits per sample and the sampling rate.

A really high-fidelity (hi-fi) recording takes up a lot of memory space (176.4 KB for every second of audio of stereo quality sampled at 16 bits, 44.1 kHz per channel).

Fortunately for most computer multimedia applications, it is not necessary to have very high fidelity sound.

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Mono Recording:

File size = Sampling rate x duration of recording in seconds x (bits per sample/8) x 1

Stereo Recording:

File size = Sampling rate x duration of recording in seconds x (bits per sample/8) x 2

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wav - standard audio file format used mainly in Windows PCs. Commonly used for storing uncompressed, CD-quality sound files.

mp3 - the MPEG Layer-3 format is the most popular format for downloading and storing music.

au - the standard audio file format used by Sun, Unix and Java. The audio in au files can be uncompressed or compressed.

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The WAV file format is a Microsoft specification for the storage of multimedia files.

A WAV file starts out with a file header followed by a sequence of data chunks.

A WAV file consists of two sub-chunks ◦ a "fmt " chunk specifying the data format

◦ a "data" chunk containing the actual sample data.

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Length Name Description

4 ChunkID Contains the

letters "RIFF" in

ASCII form

4 ChunkSize This is the size of

the

entire file in

bytes minus 8 bytes

for the

two fields not

included in this

count:

ChunkID and

ChunkSize.

4 Format Contains the

letters "WAVE"

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The "WAVE" format consists of two subchunks: "fmt " and "data":

The "fmt " subchunk describes the sound data's format:

The "data" subchunk contains the size of the data and the actual sound:

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Length Name Description

4 Subchunk1ID Contains the letters "fmt "

4 Subchunk1Size 16 for uncompressed case. This is the size of the

rest of the Sub-chunk which follows this number.

2 AudioFormat Uncompressed = 1 , Values other than 1 indicate

some form of compression.

2 NumChannels Mono = 1, Stereo = 2, etc.

4 SampleRate 8000, 44100, etc.

4 ByteRate == SampleRate * NumChannels * BitsPerSample/8

2 BlockAlign == NumChannels * BitsPerSample/8

2 BitsPerSample 8 bits = 8, 16 bits = 16, etc.

2 ExtraParamSize if uncompressed, then doesn't exist

X ExtraParams space for extra parameters

4 Subchunk2ID Contains the letters "data"

4 Subchunk2Size == NumSamples * NumChannels * BitsPerSample/8

This is the number of bytes in the data.

* Data The actual sound data.

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Audio data when sent over the Internet with a low bit rate connection, should be compressed. Discuss the importance of the audio data compression.

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