1. Chapter 5:- Sound
Eyad Alshareef
Eyad Alshareef

2. Topics: Introduction to Sound How is Sound Produced? Sampling
Storing Audio Data
File Format
Eyad Alshareef

3. Introduction to Sound
Sound is created by vibration of matter (i.e., air molecules).
It is a complex relationship involving:
a vibrating object (sound source)
a transmission medium (usually air)
a receiver (ear) and;
a preceptor (brain).
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4. The Power of Sound Sound is measured in dB (decibel)
Sound waves are known as waveforms.
Eyad Alshareef

5. Introduction to Sound 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)
One cycle = 1 Hz
Sometimes written as kHz or kiloHertz (1 kHz = Hz)
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7. Note That:-
Optimally, people can hear from 20 Hz to 20,000 Hz (20 kHz)
Sounds below 20 Hz are infrasonic
sounds above 20 kHz are ultrasonic.
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8. Introduction to Sound Time for one cycle distance along wave Cycle
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9. Introduction to Sound Sound is the best way to attract attention.
Often audio provides the only effective way to convey an idea, elicit an emotion, or dramatize point.
Sounds also can be combined in a multimedia presentation to provide information and enhance the other media being presented.
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10. Why Sound is Important in Multimedia?
To reinforce message or theme
To set the mood
To catch the interest of the audience
To alert the audience
To include narration: effective for training and educational application.
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11. Types of Sound Music Speech Background Attention grabber
Sound effect (brain.fm)
Speech
Narration
Instruction
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12. Sound Wave Characteristics
Sound is described in terms of two characteristics:
Frequency (or pitch)
Amplitude (or loudness)
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13. Sound Wave Characteristics
Frequency: is the number of cycles a sound wave creates in one second.
A cycle is measured from one wave peak to another.
The standard measurement for frequency is called HERTZ (Hz).
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14. Sound Wave Characteristics
Amplitude is the volume or loudness a particular sound makes.
The louder the sound, the higher the amplitude will be.
The unit of measure for loudness or volume is decibel (dB).
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16. Sound Wave Characteristics
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17. Digital Sound
Refers to the reproduction and transmission of sound stored in a digital format.
The digitizing and storage of sound or music on a computer or compact disc.
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18. Conversion
A digital audio signal starts with an analog-to-digital converter(ADC) that converts an analog signal to a digital signal.
After being sampled with the ADC, the digital signal may then be altered in a process which is called digital signal processing
The digital audio signal may then be stored or transmitted.
The last step for digital audio is to be converted back to an analog signal with a digital-to-analog converter(DAC).
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19. Conversion
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20. Capture and playback of digital audio
Air pressure
variations
DAC
Converts back into voltage
Digital to
Analogue
Converter
Captured via
microphone
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Air pressure
variations
ADC
Signal is
converted into
binary (discrete form)
Analogue
to Digital
Converter

21. 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
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22. The Analogue to Digital Converter (ADC)
It will monitor the continuous analogue signal at a set rate and convert what it 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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23. Sampling Process
In order for a computer to work with audio waves, they must be converted from analog to digital form.
This is done through a process called sampling, in which every fraction of a second a sample of the audio is recorded in digital bits
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24. There are two factors that affect the quality of the digitized audio:
Sample rate
Sample size
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25. Sample Rate Sample rate is the number of times the sample is taken.
The three most common sample rates are; kHz, kHz, and 44.1 kHz.
The higher the sample rate, the more samples that are taken and, thus, the better the quality of the digitized audio.
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27. Digital sampling frequency
SCA Introduction to Multimedia
07 November 2018
Digital sampling frequency
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Lecture 7

28. Digital sampling frequency
SCA Introduction to Multimedia
07 November 2018
Digital sampling frequency
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Lecture 7

29. Sample Rate
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30. Sample Size
Sample size is the amount of information stored about the sample.
The two most common sample sizes are 8 bit and 16 bit.
An 8-bit sample allows 256 values that are used to describe audio, whereas a 16-bit sample provides 65, 536 values.
The greater the sample size, the better the quality of the audio.
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31. Sampling
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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32. Sample Size
Table below shows the file size (in bytes) for 10 seconds of digital audio given various sample rates and bit values.
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33. Channel
Two types:
Monophonic
Stereophonic
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34. Channel -Monophonic
Commonly called mono sound, mono, or non-stereo sound, this early sound system used a single channel of audio for sound output.
Monophonic sound is the most basic format of sound output.
Mono (monophonic, or monaural) is sound from a single source.
All speakers in a mono system (like an intercom) will carry the same signal.
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35. Channel -Monophonic
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36. Channel -Stereophonic
Commonly called stereo sound or just stereo, stereophonic sound divides sounds across two channels (recorded on two separate sources) then the recorded sounds are mixed so that some elements are channeled to the left and others to the right.
Stereo (stereophonic) is sound from two sources, ideally spaced apart, and reproduces sound the way we hear it naturally, with two ears.
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37. Channel -Stereophonic
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38. Calculate Sound File Size
Sound File Size = Sample rate x sample size x channel x duration
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39. Calculate Sound File Size
Example 1:
Calculate how much storage space is needed to record a 16-bit, 44.1khz, stereo music for a duration of 30 seconds.
Sound file size = x 2 x 2 x 30
= bytes
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40. Calculate Sound File Size
Example 2:
Calculate how much storage space is needed to record a 8-bit, 11khz, mono sound for a duration of 10 seconds.
Sound file size = x 1 x 1 x 10
= bytes
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41. Guidelines Consider the appropriateness of using sound.
Start with the highest-quality sound available and reduce the file size by converting the audio file to a compressed format.
Consider using sound and still images as an alternative to video to reduce file sizes.
If appropriate, provide a way to give the user some control over the audio.
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42. File Formats •Wav audio (.wav) •MP3 audio (.mp3)
• AIFF (Audio Interchange File Format)
•Real audio (.ra, rm)
•MIDI (.mid)
•Windows Media (.wma)
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43. MIDI (Musical Instrument Digital Interface)
MIDI is a standard for specifying a musical performance
Rather than send raw digital audio, it sends instructions to musical instruments telling them what note to play, at what volume, using what sound, etc.
The synthesiser that receives the MIDI events is responsible for generating the actual sounds. Example: Keyboard Piano
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44. Audio File Formats
There are a number of different types of Audio files. The most common are Wave files (wav) and MPEG Layer-3 files (mp3).
The way the audio is compressed and stored is call the codec which determines how small the file size is. Some file types always use a particular codec. For example, ".mp3" files always use the "MPEG Layer-3" codec.
Other files like ".wav" files support selectable codecs. For example, a ".wav" file can be encoded with the "PCM", "GSM6.10", "MPEG3" and many other codecs.
Be careful not to confuse the file type with the codec - it often surprises to know you can have a "MPEG Layer-3" encoded ".wav" file.
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45. Audio File Formats
Some file types just contain the audio. But other file types can contain additional header information which can contain other information about the file (eg .you can have information about the sender, priority, notes and other data in the file itself).
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46. There are three categories in which an Audio file belongs
Uncompressed : - Audio Files that are not compressed and Likely have large file size (wav)
Lossless:- Audio files that are compressed but doesn't loose any quality to the file(wma)
Lossy:- Audio files that lose some quality when its being compressed (mp3)
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47. Wav VS MP3
Wav - standard audio file format used mainly in Windows PCs. Commonly used for storing uncompressed (PCM), CD- quality sound files, which means that they can be large in size - around 10MB per minute of music. It is less well known that wave files can also be encoded with a variety of codecs to reduce the file size (for example the GSM or mp3 codecs).
mp3 - the MPEG (Moving Picture Expert Group)Layer-3 format is the most popular format for downloading and storing music. By eliminating portions of the audio file that are essentially inaudible, mp3 files are compressed to roughly one-tenth the size of an equivalent PCM file while maintaining good audio quality.
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48. Real Audio Vs MIDI Real Audio (.ra .ram .rm)
Real Audio is a proprietary format, and is used for streaming audio that enables you to play digital audio files in real-time. To use this type of file you must have RealPlayer (for Windows or Mac). Real Audio was developed by RealNetworks.
MIDI - Musical Instrument Digital Interface (.mid)
Short for musical instrument digital interface, MIDI is a standard adopted by the electronic music industry for controlling devices, such as synthesizers and sound cards, that emit music. At minimum, a MIDI representation of a sound includes values for the note's pitch, length, and volume. It can also include additional characteristics, such as attack and delay time.
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55. Streaming Audio What is it? Advantages: Disadvantages:
Play almost immediately after the request, continues playing the transferring data.
Advantages:
Address the problem of long download time.
Control distribution and protect copyright, because the user cannot get a copy of the file.
Disadvantages:
Sound quality may be affected by low speed or unstable Internet connection.
CSC1720 – Introduction to Internet
All copyrights reserved by C.C. Cheung 2003.

56. What is Streaming? CSC1720 – Introduction to Internet
All copyrights reserved by C.C. Cheung 2003.