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Sound

Pertemuan 6

Matakuliah : T0732 / Sistem Multimedia

Tahun : 2007


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Learning OutcomesPada akhir pertemuan ini, diharapkan mahasiswa akan

mampu :

Menunjukkan Penggunaan Suara pada AplikasiMultimedia


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Outline Materi Sound

Waveforms

Analogue to Digital Converter (ADC) Digital Audio

MIDI (Musical Instrument Digital Interface)

Using Sound


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Sound Sound are rapid vibrations that are transmitted as variationsin air pressure

Sound comprises the spoken word, voices, music and evennoise.

As the sound vibrates it bumps into molecules of thesurrounding medium causing pressure waves to travel away

from the source in all directions

Types of Sound in Multimedia: Speech Music

Sound Effect


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Waveforms Sound waves are manifest as waveforms

A waveform that repeats itself at regular intervals is

called a periodic waveform

Waveforms that do not exhibit regularity are called

noise

The unit of regularity is called a cycle

This is known as Hertz (or Hz) after Heinrich Hertz

One cycle = 1 Hz

Sometimes written as kHz or kiloHertz (1 kHz = 1000 Hz)


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Waveforms

distance

along waveCycle

Time for one cycle


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The characteristics of sound waves Sound is described in terms of two characteristics:

Frequency Amplitude (or loudness)

Frequency the rate at which sound is measured Number of cycles per second or Hertz (Hz) Determines the pitch of the sound as heard by our ears The higher frequency, the clearer and sharper the sound the higher pitch of

sound

Amplitude Sounds intensity or loudness The louder the sound, the larger amplitude.

In addition, all sounds have a duration and successive musical sounds iscalled rhythm


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The characteristics of sound waves

distance

along waveCycle

Time for one cycleAmplitude

pitch


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Example waveforms

PianoPiano

Pan flutePan flute

Snare drumSnare drum


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Capture and playback of digital audioAir pressure

variations

Captured via

microphone

Air pressure

variations

ADC

Signal isconverted into

binary

(discrete form)

0101001101

0110101111

Analogueto DigitalConverter

DAC

Convertsback into

voltage

Digital toAnalogueConverter


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The Analogue to Digital Converter (ADC) An ADC is a device that converts analogue signals into digital signals

An analogue signal is a continuous value It can have any single value on an infinite scale

A digital signal is a discrete value It has a finite value (usually an integer)

An ADC is synchronised to some clock

It will monitor the continuous analogue signal at a set rate and convert whatit sees into a discrete value at that specific moment in time

The process to convert the analogue to digital sound is called Sampling.Use PCM (Pulse Code Modulation)


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Digital sampling - Sampling frequency


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Digital sampling - Sampling frequency


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Sampling Parameters Sampling Rate Frequency of sampling Measure in Hertz

The higher sampling rate, higher quality soundbut size storage is big.

Standard Sampling rate: 48.000 kHz (DAT) - Digital Audio Tape, also DVD

44.100 kHz (CD) - Compact Disk - typical quality ofmost sound cards

22.255 kHz - Medium quality 11.025 kHz - Low quality (frequently used for

speech)


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Sampling Parameters Size sample

The resolution of a sample is the number of

bits it uses to store a given amplitude value,e.g.

8 bits (256 different values)

16 bits (65536 different values)

A higher resolution will give higher quality but

will require more memory (or disk storage)


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Size sample


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Quantisation Samples are usually represented the audio sample as a

integers(discrete number) or digital

1 5


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Calculating the size of digital audio The formula is as follows:

The answer will be in bytes

Where:

sampling rate is in Hz

Duration/time is in seconds

resolution is in bits (1 for 8 bits, 2 for 16 bits)

number of channels = 1 for mono, 2 for stereo, etc.

8

channelsofnumberresolutiondurationrate


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Calculating the size of digital audio Example:

Calculate the file size for 1 minute, 44.1 KHz, 16 bits, stereo

sound

Where: sampling rate is 44,100 Hz

duration/time is 60 seconds

resolution is 16 bits

number of channels for stereo is 2

8

channelsofnumberresolutiondurationrate

44100 * 60 * 16 *2

8


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Digital audio editing software One of the most powerful and professional PC-based software is previously

known as Cool Edit. Its now known as Adobe Audition. Same program,

new company.


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Editing Digital Audio Simple audio editing software allows:

Recording of digital audio segments

Trimming

Splicing and assembly

Volume adjustments of the entire segment

Reversing Sounds

Copy, cut, paste and delete segments of digital audio

Others audio editing software: Sound Forge

Gold Wave

PROSONIQ SonicWORX

Samplitude Studio


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Audio formats .WAV (Developed by IBM and Microsoft)

.AU (UNIX)

.AIFF (Audio Interchange File Format) .MP3 (MPEG layer 3)

.SND (Mac)

.RA (RealAudio)

.WMA (Windows Media Audio) .VOC (SoundBlaster)


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MIDI (Musical Instrument Digital Interface) MIDI is a standard for specifying a musical performance

It allows different electronic devices to communicate

together Rather than send raw digital audio, it sendsinstructions to musical instruments telling them what note toplay, at what volume, using what sound, etc.

The synthesiser that receives the MIDI events is responsible

for generating the actual sounds. Example: Keyboard Piano

MIDI data is not digitized sound: it is a shorthandrepresentation of music stored in numeric form


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MIDI Setup


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MIDI sequencers A MIDI sequencer

allows musicians to

edit and create

musical compositions

like a word processor Cut and paste

Insert / delete


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Advantages of MIDI MIDI files are compact; the size of the file is completely

independent of playback quality

In some cases MIDI may sound better than digital audio (ifthe MIDI sound source is of high quality)

MIDI data is completely editable: you can change thelength of a MIDI file by varying its tempo without changingthe pitch

Still used a lot in studio environment to connectsynthesizers and other equipment


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Disadvantages of MIDI MIDI does not represent sound but musical

instruments, so playback is very rarely accurate(usually same score, wrong instrument)

MIDI cannot easily be used to play spokendialog

An old format, people have already begunforgetting it


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MIDI Versus Wav Quality recording, MIDI depend to the tools

Audio .wav easier to create compare than MIDI

MIDI Advantages File Size small

Size Storage also small

MIDI Disadvantages Playback

Cost and Skill


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How audio can be used effectively Cautions and warnings

It is a good medium for alerting users to criticalinformation. Some uses include:

Sounding an alarm when a limit is reached Alerting users when data is entered incorrectly

Music and Sound Effects

These make multimedia interaction more real. Someuses include:

Musical background for a video segment

Birds Songs accompanying photographs in biological fieldtraining


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How audio can be used effectively Sound-related data.

Some uses include: Helping mechanics diagnose engine trouble

Training medical students to recognize different breathingsounds

Direct voice communication.

Some uses include: Leaving a voice message for other users of an application

Consulting with an expert during a troubleshooting procedure.


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Advantages and Disadvantages of using audio Sound adds life to any multimedia application and

plays important role in effective marketingpresentations

Advantages Ensure important information is noticed

Add interest

Can communicate more directly than other medi

Disadvantages Easily overused Requires special equipment for quality production

Not as memorable as visual media


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Adding Sound to Multimedia Project Decide what kind of sound is needed and where youll

use them

Decide when to use midi and when to use digital audio

Acquire source material

Edit the sounds to fit your project

Test the sounds to be sure they are timed properly

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