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Audio 1 > Analogue and Digital Signals > Flashcards

Analogue and Digital Signals Flashcards

1
Q

Analog

A

continuously changing waveform

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2
Q

Digital

A

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

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3
Q

Sampling Rate (3)

A
  • 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
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4
Q

Bit Depth (3)

A
  • 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.
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5
Q

Pulse Code Modulation (PCM)

A

the sampling rate of an audio CD is 44.1 kHz

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6
Q

Nyquist-Shannon Sampling Theorem (2)

A
  • 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.
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7
Q

resolution of the converter (4)

A
  • 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
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8
Q

least significant bit (LSB) voltage (2)

A
  • 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
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9
Q

Digital audio bit system

A

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

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10
Q

Digital Audio Sampling

A

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.

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11
Q

Mp3 Bit Rate

A

128-160 Kbit/s

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12
Q

AudioCD Bit Rate

A

1411.2 Kbit/s

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13
Q

VideoCD Bit Rate

A

1 Mbit/s

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14
Q

DVD Bit Rate

A

5 Mbit/s

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15
Q

HDTV Bit Rate

A

20Mbit/s

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16
Q

Signal Compression (2)

A
  • 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.
17
Q

Compression and Digital Video

A

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

18
Q

CODEC (Coder/Decoder)

A

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.

19
Q

Container

A

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.

20
Q

Containers

A
  • File structure
  • Defines how data is arranged
  • MOV, AVI, WMV, MPEG-2
21
Q

Codecs

A
  • Compression algorithms

- COmpression/ DECompression

22
Q

Digital Formats (12)

A
  • MP3
  • CD
  • WAV
  • WMA
  • MPEG
  • WMV
  • AVI
  • MOV
  • ASF
  • MJPEG
  • DivX
  • Sorenson
23
Q

MP3

A

MPEG1-Audio Layer 3

24
Q

CD

A

Compact Audio Disc

25
Q

WAV

A

Waveform Audio Format (Microsoft)

26
Q

WMA

A

Windows Media Audio

27
Q

MPEG

A

Moving Picture Experts Group

28
Q

WMV (Windows Media Video)

A

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

29
Q

AVI (Audio Video Interleave)

A

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

30
Q

MOV (Quicktime(R))

A

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

31
Q

ASF (Advanced Systems Format)

A

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

32
Q

MJPEG

Motion-Joint Picture Experts Group

A

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.

33
Q

DivX

A

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

34
Q

Sorenson

A

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

35
Q

MPEG-1

A

No longer in widespread use

36
Q

MPEG-2

A

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

37
Q

MPEG-4

A

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

38
Q

Lossless Compression

A
  • 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.
39
Q

Lossy Compression

A

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

Audio 1 (8 decks)

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