Chapter 6: Digital Audio Technology Key
1. The Phonograph was invented by Thomas Edison.
2. The first version of the phonograph contained a needle that cut grooves on a tin foil.
3. Sound is caused by physical disturbances of air molecules.
4. Sound is classified as a mechanical wave.
5. One fundamental difference between sound waves and water waves is the direction of displacement of water
molecules and air molecules.
6. A speaker converts sound waves into electricity.
7. A speaker contains a diaphragm that vibrates in proportion to the sound impinging on it.
8. The audio signal generated at the microphone’s output is a digital signal.
9. Sound may be classified as either pure sound or complex sound.
10. One example of a nearly pure sound is human speech.
11. When captured by a microphone, a pure sound is a signal that varies in a non-sinusoidal manner
12. Amplitude is defined to be the time a wave requires to complete a single cycle; it is measured in seconds(s).
13. The unit of frequency is Volts
14. If 20 cycles of a wave are completed in 1 second, the frequency of the wave is 20 Hz.
15. Period and frequency are inversely related. i.e. one decreases as the other one increases.
16. 1MHz is equivalent to 1,000,000 Hz
17. 1 ns is equivalent to 1/1,000,000 s
18. The frequency of a sound wave affects the pitch of sound that we hear.
19. Pitch is a value that describes the degree to which two waves are aligned, or in synch with each other.
20. Each pure sound component that makes up a complex sound is often called a frequency component.
21. Every person’s voice has an identical frequency composition.
22. To determine the highest and lowest frequency values within a complex sound, the audio signal can be
applied to a device called a spectrum analyzer.
23. The first step in digitizing an audio signal is quantizing.
24. The sampling process that is used to digitize an audio signal is implemented by a circuit called the ADC.
25. Before assigning binary codes to the samples, each must be quantized, or rounded off, to one of a finite
number of voltages.
26. The Nyquist sampling theorem, states that the minimum number of samples per second (the sampling
frequency, or fs) required to perfectly reconstruct the analog signal should equal at least twice the value of the
difference between the signal’s highest frequency component (fmax) and lowest frequency component (fmin).
27. The standard number of bits assigned to each sample within the telephone network is 10 bits.
28. The standard sampling rate when digitizing audio signals for CD quality music is 44.1 kHz.
29. Quantization error can be reduced by taking more samples per second of the audio signal.
30. Aliasing occurs when a signal is sampled at a rate higher than the Nyquist rate.
31. Compression techniques fall into two high-level categories: Lossy compression and lossless compression.
32. The process of compressing information in consideration of the limitations of human senses is called
perceptual coding.
33. Advanced Audio Coding (AAC) is a lossless compression format.
34. Windows Media Audio (WMA) is an audio file format designed for the Microsoft Windows Media Player,
software that is used to play multimedia on the Windows operating system.
35. The tin-coated cylinders of the early phonographs were ultimately replaced by ____________________.
36. Sound is caused by physical disturbances of ____________________.
37. When sound waves reach the human ear, variations in air pressure of the ____________________ wave
cause the eardrum to vibrate in proportion to the pressure variations.
38. Sound waves are classified as ____________________ waves and water waves are a combination of
transverse and longitudinal waves.
39. Microphones capture sound waves and convert them into ____________________.
40. Part of the microphone, usually called a ____________________, mechanically vibrates in proportion to the
air pressure variations of the sound wave.
41. Sound may be classified as either ____________________ sound or ____________________ sound.
42. When captured by a microphone, a pure sound is a signal that varies in a ____________________ manner.
43. ____________________ is the magnitude of the signal at a given instant in time (t).
44. ____________________ is the time a wave requires to complete a single cycle; it is measured in seconds
(s).
45. ____________________, measured in hertz (Hz), is the number of cycles a wave completes in one second
(s).
46. Frequency is related to ____________________ and amplitude is related to____________________ of
sound that we hear.
47. In addition to amplitude and frequency, pure sounds are also described in terms of their
____________________ difference.
48. Each pure sound component that makes up a complex sound is often called a ____________________
component.
49. In audio digitization, you must have information about the ____________________ content of the audio
signal to be digitized.
50. To determine the highest and lowest frequency values within a complex sound, the audio signal can be
applied to a device called a ____________________.
51. Theoretically, you can consider audio digitization to be a three-step process. This procedure is often called
____________________ and is commonly associated with digitizing audio in telephony and CD-quality music
applications.
52. Before assigning binary codes to the samples, each must be ____________________, or rounded off, to one
of a finite number of voltages.
53. The difference between the highest and lowest frequency components is also known as the signal
____________________.
54. The standard sampling rate for digital music in the music industry is ____________________ kHz.
55. ____________________ error is the difference between the actual value of the sample and the value to
which the sample is rounded off.
56. If a signal is sampled at a rate that is lower than the Nyquist rate during digitization, the reconstructed signal
is said to undergo ____________________ into a new form.
57. The limitations of ____________________ abilities, such as hearing, enable the compression of audio.
58. Compression techniques fall into two high-level categories: ____________________ compression and
____________________ compression.
59. Digital audio formats compress audio by actually eliminating some information, but not enough to be
readily detectable by human hearing. This diminishment of the original data into fewer bits is called a loss of
____________________.
60. On average, people cannot hear any frequency lower than ____________________ Hz or above
____________________ Hz.
61. The perceptual phenomenon of filtering out less dominant information is called ____________________.
62. The advent of the ____________________ compression format has led to an enormous boost in digital
music access and exchange.
63. ____________________ is another uncompressed format. Its lossless nature makes it popular for playing
high-quality music on Apple computers.
64. The ease of downloading, reproducing, and sharing files has led to what the recording industry calls music
____________________, the illegal downloading of music. Parties on both sides of this debate use innovative
technical approaches to try to gain an advantage: music downloaders illegally obtain music through peer-to-peer
networks, while music copyright holders have instituted ______________________________ techniques to try
to thwart illegal file sharing.
65. Which of the following was invented by Thomas Edison?
66. Who is regarded as the inventor of magnetic audio recording?
67. Sound is classified as what type of wave?
68. A water wave is classified as what type of wave?
69. Which of the following devices converts sound into electricity?
70. Which of the following devices converts electricity into sound?
71. Which of the following is part of a microphone that vibrates in proportion to the sound impinging on it?
72. Which of the following devices replaced tin-coated cylinders?
73. Which of the following generates a nearly pure tone?
74. Which type of sound varies in a sinusoidal manner?
75. Which of the following properties of a wave is related to the magnitude of the wave at a given instant in
76. Which of the following properties of a wave is related to the number of cycles of the wave completed in one
second?
77. Which of the following properties of a wave is measure in terms of Hertz?
78. What happens to the period of a wave as its frequency increases?
79. How many cycles of a wave are completed in one second if the frequency of the wave is 20kHz?
80. How many cycles of a wave are completed in one second if the frequency of the wave is 5MHz?
81. How many cycles of a wave are completed in one second if the frequency of the wave is 2.5 GHz?
82. How many ms seconds is 0.001s?
83. How many ns seconds is 0.000001s?
84. How many ìs seconds is 0.000001s?
85. How many ms seconds is 0.001s?
86. How many frequency components are found within a pure sound?
87. Which of the following devices is used to display the frequency composition of an audio signal?
88. Which of the following are the steps of the audio digitization process?
89. What is the minimum sampling frequency that should be used to avoid aliasing if a complex sound has 4
frequency components with frequencies of 200 Hz, 400 Hz, 500 Hz and 800 Hz during the digitization process?
90. What is the bandwidth of a signal if it comprises of 4 frequency components with frequencies of 200 Hz,
400 Hz, 500 Hz and 800 Hz?
91. What is the bandwidth of the human voice assumed to be during the audio digitization process?
92. What is the minimum standard sampling frequency that is used to digitize audio signals within the telephone
network?
93. Calculate the quantization error if the actual value of a sample is 4 V and is rounded off to 4.4 V.
94. How can quantization error be reduced during the audio digitization process?
95. Which of the following are compressed audio file formats?
96. Which of the following digital audio file formats relies on perceptual coding?
97. Discuss how sound is created.
98. Discuss the relationship between frequency and period.
99. Discuss the effect that the frequency and amplitude of a sound wave have on the sound that we hear.
100. List the 3 steps of the audio digitization process.
101. Discuss the considerations when choosing a value for the number of bits to assign per sample during the
audio digitization process.
102. Define the term “quantization error”.
103. List the digital audio file formats discussed in the book