CEN-444
Networks Structure And Protocols
Mohammed Saleem Bhat m.bhat@mu.edu.sa
Computer Engineering and Networks, College of Engineering , Majmaah University

• Introduction to sound.
• Multimedia system sound.
• Digital audio.
• MIDI audio.
• Audio file formats.
Computer Engineering and Networks, College of Engineering , Majmaah University

• MIDI versus digital audio.
• Adding sound to multimedia project.
• Professional sound.
• Production tips.
Computer Engineering and Networks, College of Engineering , Majmaah University

• Vibrations in the air create 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 (see p.
91)
Computer Engineering and Networks, College of Engineering , Majmaah University

• Sound is energy, caused by molecules vibrating
• 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.
Computer Engineering and Networks, College of Engineering , Majmaah University

• You need to know
– How to make sounds
– How to record and edit sounds on the computer
– How to incorporate sounds into your multimedia project
Computer Engineering and Networks, College of Engineering , Majmaah University

• System sounds are assigned to various system events such as startup and warnings, among others.
• Macintosh provides several system sound options such as glass, indigo, laugh.
• In Windows, available system sounds include start.wav, chimes.wav, and chord.wav.
• Multimedia sound is either digitally recorded audio or MIDI (Musical Instrumental Digital
Interface) music.
Computer Engineering and Networks, College of Engineering , Majmaah University

• Most computers have sounds ready to use
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• Mac and Windows have built in sound recorders
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• Windows system sounds are .WAV files in the
Windows\Media directory
• MS Office includes additional sounds
• You can add your own sounds by including them in the Windows\Media directory and selecting them from the Sound Control Panel
Computer Engineering and Networks, College of Engineering , Majmaah University

• MIDI is a series of musical instructions
Click to play
Computer Engineering and Networks, College of Engineering , Majmaah University

• MIDI ( 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.
Computer Engineering and Networks, College of Engineering , Majmaah University

• MIDI data is NOT digitized sound- it is music stored in numeric format
• Digital audio is a recording, which depend on your sound system
• MIDI is a score and depends on both the quality of the instruments and the sound system
• Quality depends on end user’s device rather than on the MIDI device and is device dependent.
Computer Engineering and Networks, College of Engineering , Majmaah University

• Creating a MIDI score requires:
– Knowledge of music and some talent
– Ability to play a musical instrument
– Sequencer software
– Sound synthesizer
• Built into PC board
• Add-on for MAC
• MIDI can synthesize over 100 instruments
Computer Engineering and Networks, College of Engineering , Majmaah University

You will need:
• Sequencer Software (Smart Score)
• A Sound synthesizer ( built into PC sound board, an add on for MAC)
• MIDI keyboard or device
• Ability to play the piano and music theory background
• or a hired “expert”
Computer Engineering and Networks, College of Engineering , Majmaah University

• A MIDI file is a list of commands that are recordings of musical actions, that when sent to a MIDI player results in sound
• MIDI data is device dependent
• MIDI represents musical instruments and is not easily used to playback spoken dialog
Computer Engineering and Networks, College of Engineering , Majmaah University

• MIDI is a shorthand representation of music stored in numeric form.
• Since they are small, MIDI files embedded in web pages load and play promptly.
• Length of a MIDI file can be changed without affecting the pitch of the music or degrading audio quality.
• Working with MIDI requires knowledge of music theory.
Computer Engineering and Networks, College of Engineering , Majmaah University

• Digital audio is a representation of the original sound
• Sampling rate is measured in kilohertz
(kHz)
Click to play
Computer Engineering and Networks, College of Engineering , Majmaah University

• Digital audio represents a sound stored in thousands of numbers or samples.
• Digital data represents the loudness at discrete slices of time.
• It is NOT device dependent and should sound the same each time it is played
• It is used for music CD’s
Computer Engineering and Networks, College of Engineering , Majmaah University

• The three sampling frequencies most often used in multimedia are CD-quality 44.1 kHz, 22.05 kHz and 11.025 kHz.
• The number of bits used to describe the amplitude of sound wave when sampled, determines the sample size.
• Digital audio is device independent.
• The value of each sample is rounded off to the nearest integer (quantization).
Computer Engineering and Networks, College of Engineering , Majmaah University

Computer Engineering and Networks, College of Engineering , Majmaah University

• Balance file size versus quality

To calculate file size in bytes:
Mono: sampling rate  duration of recording in seconds  (bit resolution  8)  1
Stereo: sampling rate  duration of recording in seconds  (bit resolution  8)  2
Computer Engineering and Networks, College of Engineering , Majmaah University

• Once a recording had been completed, it almost always needs to be edited.
• Basic sound editing operations include: trimming, splicing and assembly, volume adjustments and working on multiple tracks.
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Additional available sound editing operations include format conversion, resampling or downsampling, fade-ins and fade-outs, equalization, time stretching, digital signal processing, and reversing sounds.
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• MIDI data and digital audio are like vector and bitmapped graphics:
• Digital audio like bitmapped image – samples original to create a copy
• MIDI – like vector graphic- stores numeric data to recreate sound
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• MIDI data is device dependent; digital audio is not
• MIDI sounds (like vector graphics) are different on different devices;
• Digital sounds are identical even on different computers or devices.
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• MIDI file are much more compact and take up less memory and system resources
• MIDI files embedded in web pages load and play much faster than digital
• You can change the length of a MIDI file by varying its tempo
• With high quality MIDI devices, MIDI files may actually sound better than digital
Computer Engineering and Networks, College of Engineering , Majmaah University

• MIDI represents musical instruments not sounds and will be accurate only if your playback device is identical to the production device
• MIDI sound is inconsistent
• MIDI cannot be easily used to reproduce speech
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• Digital audio sound is consistent and device independent
• A wide selection of software support is available for both MAC and PC
• A knowledge of music theory is not required for creating digital audio, but usually is needed for MIDI production
Computer Engineering and Networks, College of Engineering , Majmaah University

• If you don’t have enough RAM memory, or bandwidth for digital audio
• If you have a high quality sound source
• If you have complete control over the playback hardware
• If you don’t need spoken dialog
Computer Engineering and Networks, College of Engineering , Majmaah University

• If you don’t have control over the playback hardware
• If you have the computing resources and bandwidth to handle the larger digital files
• If you need spoken dialog
Computer Engineering and Networks, College of Engineering , Majmaah University

• You can digitize sound from a microphone, synthesizer, tape recording TV broadcast, or
CD’s.
• Digitized sound is sampled every nth of a second. The more often you take the sample, the better the sound.
• Sample sizes are either 8 or 16 bits and common frequencies are11.025, 22.05, and
44.1 kHz (See pp. 209- 211)
Computer Engineering and Networks, College of Engineering , Majmaah University

• To prepare digital audio from analog media, record it from a device, like a tape recorder, into your computer using digitizing software.
• Balance the sound quality with your available
RAM
• Set proper recording levels for a good clear recording
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• Audio resolution determines the accuracy with which a sound is digitized. (More bits in the sample size produces better quality and larger files)
• Stereo recordings are more realistic and require twice as much storage space and playback time.
• Mono files tend to sound “flat”
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• Apple’s QuickTime Player Pro provides for primitive playback and editing
• Sonic Foundry’s Sound Forge is a more serious sound editor
• These can be used to trim, splice, volume adjustment and format conversion as well as special effects
Computer Engineering and Networks, College of Engineering , Majmaah University

• A sound file’s format is a recognized methodology for organizing data bits of digitized sound into a data file.
• 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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• CD-ROM/XA (Extended Architecture) format enabled several recording sessions to be placed on a single CD-R (recordable) disc.
• Linear Pulse Code Modulation is used for Red
Book Audio data files on consumer-grade music CDs.
Computer Engineering and Networks, College of Engineering , Majmaah University

• To play MIDI sound on the web
– wait for the entire file to download and play it with a helper application
– stream the file, storing it in the buffer and playing it while it downloads
• Streaming is dependent on the connection speed
• FLASH allows sound to be integrated in a multimedia presentation, controlled by buttons and saved as .mp3
Computer Engineering and Networks, College of Engineering , Majmaah University

• Decide what sounds you will need and include them in the story board or cue sheet.
• Decide whether to use MIDI or digital audio
• Acquire source material (record/buy)
• Edit the sounds
• Test the sounds to be sure they are timed properly
Computer Engineering and Networks, College of Engineering , Majmaah University

• CD- quality audio
 Standard is ISO 10149, a.k.a. the “Red Book Standard”
 Sample size is 16-bit
 Sample rate is 44.1 kHz
 11 seconds of audio uses 1.94 MB of space
Computer Engineering and Networks, College of Engineering , Majmaah University

• The Red Book Standard- ISO 10149
– ( 16 bits at 44.1 kHz) allows accurate reproduction of all sounds humans can hear
– Software such as Toast and CD-Creator can translate digital files from CD’s directly into a digital sound editing file or decompress.mp3 files into CD-Audio
Computer Engineering and Networks, College of Engineering , Majmaah University

• Compression techniques reduce space but reliability suffers.
• Space can be conserved by downsampling or reducing the number of sample slices taken per second.
• File size of digital recording (in bytes) = sampling rate X duration of recording (in secs) X (bit resolution/8) X number of tracks.
Computer Engineering and Networks, College of Engineering , Majmaah University

• Scripting Languages such as Open Script
(Toolbook), LINGO(Director), or Action
Script ( FLASH) provide better control over audio playback
• Requires some programming knowledge
Computer Engineering and Networks, College of Engineering , Majmaah University

• Vaughn’s Law of Minimums - there is an acceptable level of adequacy that will satisfy the audience;
• If your handheld microphone is good enough to satisfy you and your audience, conserve your money and energy.
Computer Engineering and Networks, College of Engineering , Majmaah University

• Recording on inexpensive media rather than directly to disk prevents the hard disk from being overloaded with unnecessary data.
• The equipment and standards used for the project must be in accordance with the requirements.
• Sound and image synchronization must be tested at regular intervals
Computer Engineering and Networks, College of Engineering , Majmaah University

• Audio recording - use CD’s, or VCR tapes, or
DAT ( digital audio tape) tapes
• Create a good database to organize your sounds, noting the counter and content
• Testing and Evaluating- (delaying a fast machine if needed to sync with animation)
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• Copyright Issues
• Securing permission for the use of sounds and music is the same as for images
• Can buy royalty-free digitized sound clips
• DO NOT use someone’s original work without permission!
Computer Engineering and Networks, College of Engineering , Majmaah University

• Vibrations in air create waves of pressure that are perceived as sound.
• Multimedia system sound is digitally recorded audio or MIDI (Musical Instrumental Digital Interface) music.
• Digital audio data is the actual representation of a sound, stored in the form of samples.
Computer Engineering and Networks, College of Engineering , Majmaah University

• MIDI is a shorthand representation of music stored in numeric form.
• Digital audio provides consistent playback quality.
• MIDI files are much smaller than digitized audio.
• MIDI is device dependent digital audio is not
• MIDI files sound better than digital audio files when played on high-quality MIDI device.
Computer Engineering and Networks, College of Engineering , Majmaah University