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Sound Structure : The power of Sound Digital Audio MIDI Audio MIDI Vs Digital audio Multimedia system sounds Audio File Formats Vaughan’s Law of Multimedia Minimums Adding sound to Multimedia project

Multimedia chapter 4

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Page 1: Multimedia chapter 4

SoundStructure :

The power of SoundDigital AudioMIDI AudioMIDI Vs Digital audioMultimedia system soundsAudio File FormatsVaughan’s Law of Multimedia MinimumsAdding sound to Multimedia project

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The Power of Sound Vibrations in the air creates waves of pressure that are perceived as sound.

Sound waves vary in sound pressure level (amplitude) and in frequency or pitch.

‘Acoustics’ is the branch of physics that studies sound.

Sound pressure levels (loudness or volume) are measured in decibels (dB).

Humans hear sound over a very broad range

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The Power of Sound

Sound is energy, caused by vibrations of the molecules.

Too much volume can permanently damage your ears and hearing.

The perception of loudness depend on the frequency or pitch.

Harmonics cause the same note played on a cello to sound different from one played on a piano.

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Digital AudioDigital audio is created when you represent the characteristics of sound wave using numbers - a process referred to as Digitizing.

We can digitize any sound.( Microphone, synthesizer….).

Digitized sound is sampled sound.

Every nth fraction of a second , a sample of a sound is taken and stored as digital information in bits and bytes.

The quality of digital recording depends on the how often the samples are taken.i.e higher the sampling rate better is the quality of sound.

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Sampling rate is measured in KiloHertz.

Three sampling rates are normally used in Multimedia 44.1k Hz (CD- Quality) , 22.05 kHz and 11.025 kHz.

Larger the sample size , more accurate data will describe the recorded sound.

The value of each sample is rounded off to the nearest integer, called Quantization.

Digital Audio

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Making Digital Audio Files

It’s a straight forward process.

Plug a microphone in its jack , Then make use of audio digitizing software like Audacity to do the work.

2 crucial aspects to be considered :1)Balancing the need for sound quality against the file

size.(Higher Quality Larger File size).

2)Setting proper recording levels to get a good ,clean recording.

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Setting Proper Recording Levels

What type of recording to be considered?

We need to use a good piece of Digital audio recording and editing software that displays digital meters.

Once the recording has been made, It will almost be necessary to edit it using the required tools available in the software.

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Basic sound Editing operations :

1. Trimming

2. Splicing and assembly

3. Volume and adjustments

4. Format conversion

5. Resampling and downsampling

Setting Proper Recording Levels

6. Fade in and Fade out

7. Equalization

8. Time Stretching

9. Digital Signal Processing

10.Reversing sounds

11.Multiple Tracks

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Setting Proper Recording Levels1. Trimming : Removing dead air or blank space and so

on. Done using commands like cut , clear , Erase, Silence.

2. Splicing and Assembly : Removal of extraneous noise , touch up, creating a longer recording by mixing many small recordings.

3. Volume adjustments : when we combine one or more recording with different volume level, they must be made to run with a consistent vol. level. We need to normalize it with a sound editor to a particular level.

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4. Format Conversion : While saving different formats are made

available for sounds. Data may be lost during conversion. MP3,MP4

5. Resampling and downsampling : if we have sound recorded and

edited the sound at 16 bit sampling rate and using lower rates then

RS & DS is necessary, as we may save lots of disk space.

6. Fade in & Fade out :useful for sections that requires this effect.

This enveloping helps to smooth out a beginning and end of the

sound file.

Setting Proper Recording Levels

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7. Equalization : allow us to modify a recordings frequency content

so that it sounds brighter or darker .

8. Time Stretching : allows to alter the length of the file . Useful but

may degrade audio quality of the file.

9. Digital Sound Processing : allows signals with reverberation, multi tap delay, chorus, flange and other special effects using DSP routines

Setting Proper Recording Levels

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Setting Proper Recording Levels10. Reversing Sound : Reversing or a part of a recording.

11. Multiple Tracks : Being able to edit and combine multiple tracks, merge tracks and then export them in a final mix to a single audio file is important.

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Musical Instrument Digital Interface :

is a communications standard developed in the 1980’s for electronic instruments and computers.

It allows instruments from different manufacturers to communicate.

But MIDI data is not digitized, its only music data stored in numeric form.

Digital Audio is recording where as MIDI is a score.

Device Independent.


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MIDIA MIDI file is a list of time stamped commands that are recordings of musical actions.

Using MIDI, we can easily and quickly compose our own original score.

The process of creating MIDI is quite different from digitizing a recorded audio.

Digitized Audio Bitmap Image then MIDI Vector graphics.

For digitized audio we simple need to play the recording through a computer device that can digitally record the sound.

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To make MIDI, we need :

Notation Software

Sequencer Software


MIDI Keyboard


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MIDI software creates data about each note as it has been played on a MIDI keyboard which note, how much pressure was put on each key, how much time the sound sustained……….

This information, when played back through MIDI device , allows the same to be reproduced exactly.


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MIDI Vs Digital AudioAdvantages :

MIDI files are more compact than audio files.

MIDI is small , can be easily embedded into the web pages.

If the MIDI sound source is of high quality, this sounds better than audio files.

MIDI data is completely editable.

MIDI data can be easily converted to musical notations and vise versa.

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Disadvantages :

MIDI does not represent sound, there fore cannot be used for sound production.

MIDI cannot be easily used to playback a spoken dialog, although expensive and technically tricky digital samplers are available.

MIDI Vs Digital Audio

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When to Use MIDI ?A. Digital audio wont work when there isn’t enough

memory or bandwidth.

B. When there is high quality MIDI sound source.

C. When we have complete control over the machine on which the program is going to be delivered.

D. We don’t need spoken dialog.

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Why should we work with Digital Audio?It has a consistent playback quality.

A wider selection of application software and system support for DA is available in Win and Mac platforms.

Preparation and programming of DA doesn’t require the knowledge of music theory.

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When to Use Digital Audio ?We don’t need control over the playback Hardware.

When we have enough bandwidth and computing resources.

When spoken dialog is required.

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Multimedia Sound SystemsWe can use sound on computer for any action performed with it.

Open the sound control panel to listen to the system sounds , change them, make new , or custom sound.

In windows, sounds are wave files, they reside in Windows/Media Sub directory.

They include chimes.wav, chord.wav , logoff.wav and so on.

In OS X on Mac system, we can only change the system alert sound.

Custom sound should be added into System/Library/Sounds subdirectory in AIF Format.

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Audio File FormatsA sound file’s format is a recognized methodology for compressing data bits of digitized sound into a data file.

The structure of the file must be known even before the data can be saved or later loaded into a computer to be edited or played as sound.

The file name extension identifies the method of storage used.

On the Macintosh, digitized sounds may be stored as data files, resources, or applications such as AIFF or AIFC.

In Windows, digitized sounds are usually stored as WAV files.

Both can use MIDI files (.mid).

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Audio File FormatsThe method used for consumer grade music CD’s is Linear Pulse Code Modulation (LPCM shortened to PCM)

CD-ROM/XA (Extended Architecture) format for reading and writing CD’s was developed later so one can put several recording sessions of music to be placed on a single CD-R .

LPCM tracks from an Audio CD are usually converted and stored on a computer in uncompressed AIFF or WAV format.

AIFF Audio Interchange File FormatWAV Wave Format

Both Contain Uncompressed data

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Audio File FormatsThere are huge number of file formats and “Multimedia Containers” that store sound data

There are converters to read and write sound files from one format to another.

MP3 was developed by MPEG (Moving Picture Expert Group).

• Common method for storing consumer audio.

• Contains lossy compression algorithm to save space.

• Evolved in early 1990’s.

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Audio File FormatsExample : An audio CD may hold an hours uncompressed LPCM, if the same content is stored in MP3 format then we can store 7 hours content with a slight loss in quality.

WMA (Windows Media Audio) is a proprietary format developed to improve MP3.

OGG was developed as an open – source and royalty free “Container” for sound compressed using the “Vorbis algorithm”.

Vorbis sound data resides within an OGG container OGG Vorbis

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Audio File FormatsMP4 format is based on Apple’s Quick Time Movies(.mov) “container” model.

It is similar to the MOV format that stores different types of media.

MP4 extension is used when file streams audio & video together.

M4a extension is used only when file contains only audio data.

M4p extension contains only audio, but encrypted for Digital Rights Management(DRM).

M4r files are used for ringtones on Apple’s iPhone.

Other GSM phones use 3gp file format for ring tones.

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Audio File FormatsAdvanced Audio Coding (AAC) format is adopted by Apple’s iTunes store.

Default format for iPod , iPhone , PlayStation ,Wii, Dsi , Motorola , Nokia , Philips , Samsung , Siemens and Sony Ericsson.

Codec is a software that compresses a stream of audio or video for data storage or transmission and then decompresses it for play back.

Some are “lossy” trade quality for reduced file size transmission speed.

Some are “lossless” original data is not at all altered.

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Vaughan’s Law of Multimedia MinimumsLiebig’s Law of Minimum :

The evolution of eyesight , loco motor speed , sense of smell , or any other species trait will cease when that trait becomes sufficiently adequate to meet the survival , requirements of the competitive environment.

If the trait is good enough , the organism expends no more effort improving it.

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Vaughan’s Law of Multimedia Minimums

There is an acceptable minimum level of adequacy that will satisfy the audience, even when that level not be the best that technology , money , or time and effort can buy.

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Adding sound to your Multimedia ProjectFollowing steps are required to bring an audio recording into MM project :

1. Determine the file formats that are compatible with MM authoring S/W .

2. Determine the sound playback capabilities that the end user’s system offers.

3. Decide the type of sound needed.

4. Decide where and when you want to use the digital audio or MIDI data

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Adding sound to your Multimedia Project5. Acquire source material by creating it from scratch or buying it.

6. Edit the sounds to fit your project.

7. Test the sounds to be sure they are timed properly with the project’s images. (This may involve steps 1-4 until everything is in sync).

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Space ConsiderationsLarge amount of digital information is required for high quality sound.

Which in turn requires large amount of space.

If monaural sound is adequate then one can cut the storage space by half or get double the playing time in the same memory space.

With compression codecs we can reduce the size to 1/8th the space but there is loss of quality.

We can also downsample.

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Space ConsiderationsThe following formula helps you to estimate your storage needs.If you are using 2 channels for stereo then double the space.

(Sampling rate * bits per sample) / 8 = bytes / sec

The same can be solved in terms of KiloBytes :

Sample rate * sample size / 8 * # sec * 2 (if stereo) = file size in KB

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Audio RecordingIf we require CD quality recording, then digitize sound at 44.1 kHz and 16 bit to store, at a sound studio.

If we decide to do it our self then we need to invest in :

acoustically treated room ,

high end amplifiers ,

recording equipments ,

powerful microphones.

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Audio RecordingDigital Audio Tape (DAT) systems provide a tape based 44.1 kHz and 16 bit record and playback capability.

DAT recordings are too accurate, precisely recording glitches, background noises, microphone pops , including coughs in the next room.

A good editor can reduce the impact of these noises but at the cost of time and money.

Mobile phones can record audio. USB , flash memory recorders can be used to record and the recordings can be downloaded directly as digital files using USB cables or card readers.

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Keeping Track of Sounds

When a project has many sounds , its important to maintain a gooddatabase , keeping a physical track of original material just in case you need to revert it when the disk drive crashes.

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Audio CD’sThe method for digitally encoding the high quality stereo of the consumer CD market is an international standard , ISO 10149.

Also known as “Red Book Audio “ standard.

Converter & burning s/w’s such as Toast and CD creator from Roxio can translate digital files of RBA found on CD directly to digital sound file formats like MP3 & WAV.

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Sound for MobileRingtones are normally associated with phones.

Telephone systems pulsating at 90 volt signal is sent to copper wire to energize the hammer like klangs a bell.

But in the present systems, the mobile’s s/w takes the charge when come one calls, depending on the programmed options, plays the users choice of ring tone.

Ring tones play on very small speakers & often compete in a noisy environment.

The other tones include answer tones , sing tones , true tones , real tones , video tones & ringles.

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Sounds for InternetThere are many methods by which we can play sound on a web page.

Sound is actually not a part of web page as it has it is a separate file with its own address & is embedded into the page.

The simplest way to embed a sound file is to se an inline HTML anchor :<a href=“sound.wav”> Click here to listen to sound </a>

The text “Click here to listen to sound “ would be underlined, when we click on it the browser will find the file mysound.wav, download it, and opens a player to play the sound.

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Sounds for InternetMedia players are designed to play files as soon as enough of the data is cached in computer’s buffer .

Downloading continues to fill the buffer faster, then you empty it by playing the sound allowing the sound file to stream .

Streaming files are dependant on connection speed:When using dial up modem, it is very slow.While using DSL , its much faster.

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Testing & EvaluationWhen lots of things are involved in a project , problems don’t emerge until we start testing.

Evaluate the sound storage medium.

Calculate the amount of RAM required and so on.

In the world of professional films & video production, sound is incorporated during post production or post session , after all the film and video footage has been assembled.