Digital audio technologies allow for the reproduction and manipulation of sound in digital form. Sound is converted from analog to digital via sampling, where the amplitude of sound waves is measured at regular intervals. This results in digital audio files that can be edited, stored and transmitted more easily than analog audio. Popular digital audio file formats include WAV, MP3, MIDI and more. Devices like the iPod and services like iTunes revolutionized portable music and digital music distribution. Technologies like text-to-speech and DAISY have also improved audio accessibility.

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2. Agenda
• Properties of sound
• Analog audio
• Digital audio
• Audio file formats
• Sound recording
• Sound editing
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3. Introduction
• Audio is the reproduction of sound - important
means of communication.
• There are a number of advantages of using
audio.
• most obvious: interface for visual disabilities
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4. Properties of Sound
• Sound is a pressure
wave created by
successively vibrating
matter back and forth.
• The sound wave is in
the form of a sine
wave.
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5. Frequency
• The number of air pressure oscillations per
second at a fixed point by a sound wave
• Measured in Hertz (Hz) - number of waves per
second
• Audible range (human) = 20 Hz - 20 kHz
• this is where the sensation of pitch
originates
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6. Frequency & Pitch
Frequency
Pitch
Frequency
Pitch
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7. Wavelength
• The distance between waves
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8. Amplitude
• The height of the
wave
• Measured in decibels
(dB or dBA)
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9. Intensity vs. Loudness
• Amplitude can be thought of as the intensity of
sound and is measurable.
• Loudness of sound is a perception.
• Sound can be perceived differently at the various
frequencies (1 kHz-4 kHz is more sensitive than
the lower and the higher)
• Individuals also have different hearing capacities.
What is loud to one person may not be loud to
another, which why loudness is a perception and
cannot be measured.
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10. dBA Sound
10 Normal breathing
20 Whispering at 5 ft
30 Soft whispering
50 Rainfall
60 Normal conversation
110 Shouting in the ear
120 Thunder
110-120 Rock concert
130 Air raid
180 Rocket launching from pad
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11. Analog Audio
• analog = the
measurement of
continuous change or
movement over a
period of time
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12. Digital Audio
• The reproduction of sound using digital
information
• The value of the signal is sampled at regular
intervals by an analog-to-digital converter
(ADC)
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13. Basic Terminology &
Properties of DA
• Channels
• Sampling rate
• Bit depth
• Quality and file size
• Compression
• Audio codecs
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14. Channels
Stereo
e s se d l
c om p r i le w i l
An u n gi t a l f
e o di e s i ze o f a
s te r c e t h
b e t w i n o f i le .
mo
Mono
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15. Sampling Rate
• ADC - the signal is sampled at regular intervals
• The value of each sample is rounded to the
nearest integer in a scale that varies according
to the resolution of the signal
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16. Sampling Rate
• The accuracy the
reproduction to
the source
depends on how
often the sample is
taken.
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17. Common DA Sampling Rate
8,000 Hz telephone, adequate for human speech
22,050 Hz radio
32,000 Hz miniDV digital camcorder
CD, commonly used with MPEG-1 audio
44,100 Hz
(VCD, SVCD, MP3)
digital sound used for digital TV, DVD, DAT,
48,000 Hz
films and professional audio
96,000 or 192,400 Hz DVD-audio and HD-DVD audio tracks
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18. Bit Depth
• The number of bits used to describe each of
the samples taken from the sampling rate
• the potential accuracy of a digital audio
• Higher bit-depth audio will sound better
than lower one
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19. Quality & File Size
• Make the highest level (if possible) ~ 16-bit
44kHz Stereo
• this produces a large file size, however, high
audio clarity
• Chances to manipulate such file (to make it
smaller) :
• reduce the sampling rate
• make it mono
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20. 20

21. Compression
Audio
Quality
“later editing”
• Digital audio files can also
be compressed to reduce Lossless
file size WMA
Lossy
• MPEG-1 Audio layer-3 MP3
Real Audio
(MP3) is a common
“transmission”
File Size
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22. Audio Codecs
• An audio codec is a piece of software
(coder/decoder)
or a driver that provides support for certain
audio formats for certain system.
codec x codec y
✘
Audio codecs codec x
✔ 22

23. Audio File Formats
• An audio file format is a
container format for storing
• WAV format
data on a computer system. • Microsoft’s audio format
• AIF format • also one of the mostthe
common format on
• developed by Apple
Computer
web
• MP3
• supported by most web
browsers • most widespread form
of audio on the Internet
• AU format
• playable on various
• one of theformat on the
common
most players
web
• created by Sun
Microsystems
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24. 24

25. MIDI Format
• Musical Instrument Digital Interface (MIDI) is
typically used to play music.
• MIDI files contain a set of instruction that the
computer sends to a sound card, synthesizer,
or other device.
• Such instructions (note and instrument
description) describe how to play the sound,
rather than recording an actual rendition of
the sound.
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26. 26

27. Sound Recording
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28. 28

29. 29

30. Sound Editing
• Audacity - it’s GNU GPL license, it’s free, it’s cross
platform.
• Tracks
• Waveform display
• Selection
• Trim
• Amplify
• Pitch
• and many more....
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31. Digital Audio
Technologies & Applications
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32. Portable Music Players
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33. Before Digital
70s
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34. CD on market (1982)
D ig i t al!
I t ’s
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35. Not quite portable, is it?
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36. Digital files?
Compress ‘em
ATRAC WMA
CODECS
MP3
Vorbis (OGG) AAC
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37. Digital Audio Players
1997 - MPMan 1998 - Rio PMP300
SaeHan Infomation Systems Diamond Multimedia
Eiger Labs MPMAN F10 (1998) 32 MB Internal Memory
32 MB SmartMedia Memory Slot
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38. Digital Audio Players
2000 - Creative NOMAD Jukebox
Creative Labs
6 GB Harddisk
$500
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39. The Revolution
October 2001 - 1st iPod Introducing
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40. iPod Family
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42. 42

43. Get quick and instant access to Tune into all your favorite stations Watch supported 720p HD movies, Connect, update, and buy content Surf the web anytime, anywhere
your content with multi-touch with crystal-clear reception. With TV shows and videos in high wirelessly from Wi-Fi hot spots. you have a Wi-Fi connection.
navigation. With a 3.3-inch screen an integrated HD Radio receiver, definition on your HDTV through Stream millions of songs over Wi- Enjoy your favorite websites with a
and vivid 16:9 OLED display you can access a variety of HD the Zune HD & AV Dock (sold Fi directly to your Zune HD and full-featured web browser including
(480x272 resolution), premium Radio stations at no additional separately). Or take them with you turn it into a portable digital tap-to-zoom technology, built-in
entertainment is at your fingertips.* cost. Plus, tag the songs you like for premium entertainment on the jukebox. accelerometer, and touchscreen
for later purchase. go. Additional dock and HDTV are QWERTY keyboard.
required.*
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44. 44

45. 45

46. iTunes
+ iTunes Music Store
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47. 47

48. Online Music Stores
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49. 49

50. Podcast
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51. 51

52. AudioBooks
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54. Text-to-Speech
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56. DAISY (Digital Accessibility
Information System)
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