Analogue and Digital Signals

Question 1

Analog

Answer 1

continuously changing waveform

Question 2

Digital

Answer 2

“Samples” the waveform at specific intervals and describes content in bits

Question 3

Sampling Rate (3)

Answer 3

• how many times, per second, a digital sample is taken of the analog signal
• determines the digital signal’s accuracy, which is how closely it captures the frequency of the original signal
• The greater the sampling rate, the greater the resolution of the digital copy

Question 4

Bit Depth (3)

Answer 4

• the number of bits used to describe a sampled voltage level
• Bit depth is also known as “quantization” because it involves assigning a quantity to the signal being measured
• Greater bit depth gives a more accurate representation of the sampled signal.

Question 5

Pulse Code Modulation (PCM)

Answer 5

the sampling rate of an audio CD is 44.1 kHz

Question 6

Nyquist-Shannon Sampling Theorem (2)

Answer 6

• an analog signal can be reconstructed if it is encoded using a sampling rate that is greater than twice the highest frequency sampled
• For example, since the range of human hearing extends to 20 kHz, the sampling rate for digital audio should be greater than 40 kHz.

Question 7

resolution of the converter (4)

Answer 7

• the number of discrete values it can produce over the range of analog values
• values are usually stored electronically in binary form, so the resolution is usually expressed in bits
• the number of discrete values available, or “levels”, is a power of two
• For example, an ADC with a resolution of 8 bits can encode an analog input to one in 256 different levels

Question 8

least significant bit (LSB) voltage (2)

Answer 8

• Resolution can also be defined electrically, and expressed in volts.
• The minimum change in voltage required to guarantee a change in the output code level

Question 9

Digital audio bit system

Answer 9

Digital audio uses a 16, 18 or even 24-bit system.

Question 10

Digital Audio Sampling

Answer 10

the base sampling rate is 44,000 times per second (44KHz), which provides for more than 2 samples to describe the highest frequency encoded by the system = 20 KHz, thus keeping in line with the Shannon-Nyquist theorem.

Question 11

Mp3 Bit Rate

Answer 11

128-160 Kbit/s

Question 12

AudioCD Bit Rate

Answer 12

1411.2 Kbit/s

Question 13

VideoCD Bit Rate

Answer 13

1 Mbit/s

Question 14

DVD Bit Rate

Answer 14

5 Mbit/s

Question 15

HDTV Bit Rate

Answer 15

20Mbit/s

Question 16

Signal Compression (2)

Answer 16

• the more you compress a signal, the more you affect its quality
• If you remove too much data, the effects can be seen in image files and heard in audio files.

Question 17

Compression and Digital Video

Answer 17

Standard DV (digital video) cameras usually compress at a ratio of 5:1. Some video formats offer much higher compression rates

Question 18

CODEC (Coder/Decoder)

Answer 18

an electronic device that converts analog signals, such as video and audio signals, into digital form and compresses them to conserve bandwidth on a transmission path.

Question 19

Container

Answer 19

the structure of a file where the data is stored. It defines how the data is arranged to increase performance and which codecs are used.

Question 20

Containers

Answer 20

• File structure
• Defines how data is arranged
• MOV, AVI, WMV, MPEG-2

Question 21

Codecs

Answer 21

• Compression algorithms

- COmpression/ DECompression

Question 22

Digital Formats (12)

Answer 22

• MP3
• CD
• WAV
• WMA
• MPEG
• WMV
• AVI
• MOV
• ASF
• MJPEG
• DivX
• Sorenson

Question 23

MP3

Answer 23

MPEG1-Audio Layer 3

Question 24

CD

Answer 24

Compact Audio Disc

Question 25

WAV

Answer 25

Waveform Audio Format (Microsoft)

Question 26

WMA

Answer 26

Windows Media Audio

Question 27

MPEG

Answer 27

Moving Picture Experts Group

Question 28

WMV (Windows Media Video)

Answer 28

Collection of Microsoft proprietary video codecs that uses a version of MPEG-4

Question 29

AVI (Audio Video Interleave)

Answer 29

Commonly contains MJPEG or DivX, but may contain a variety of codecs.

Question 30

MOV (Quicktime(R))

Answer 30

Quicktime(R)) In most cases, this is used with the locked Apple(R) codec. Quicktime can also contain other codecs such as M-JPEG

Question 31

ASF (Advanced Systems Format)

Answer 31

Early Microsoft implementation of an MPEG-4 codec- intended primarily for streaming, it is a subset of WMV

Question 32

MJPEG | Motion-Joint Picture Experts Group

Answer 32

An early encoding method, it creates a JPEG image from each frame of video. Motion effect is achieved when the images are run in series. MJPEG is still found in some consumer digital cameras.

Question 33

DivX

Answer 33

began as an ASF codec inside an AVI container. Version 4 and later versions are variations of the MPEG-4 codec.

Question 34

Sorenson

Answer 34

Apple's proprietary codec. Apple started implementing versions of the MPEG4 codec with the release of QuickTime 6.

Question 35

MPEG-1

Answer 35

No longer in widespread use

Question 36

MPEG-2

Answer 36

Lowest and common denominator for most equipment and the most common MPEG codec

Question 37

MPEG-4

Answer 37

Group of codes of which some are proprietary Microsoft and some are open.

Question 38

Lossless Compression

Answer 38

- a process that retains the original quality of a file after it has been compressed and decompressed. - WinZip(R), a popular file compression program, is an example of a program that uses lossless compression.

Question 39

Lossy Compression

Answer 39

gives an approximation of the original data by eliminating redundant or unnecessary information.