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Core Technologies > Digital Audio > Flashcards

Digital Audio Flashcards

1
Q

A/D and D/A converters, and where

A

Small piece of circuitry inside interfaces, consoles, cell phones, computers, headsets, MP3 players, CD players, DVD players, BluRay players, etc

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2
Q

A/D converters

A

Takes AC voltage and converts into Binary Code

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3
Q

D/A converters

A

Take Binary Code and converts into AC voltage

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4
Q

The Clock

A

Uses crystals (commonly quartz) to maintain a precise frequency, which regulates the movement of a timing device (watches, CONVERTERS)

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5
Q

Why is the Clock important in a converter?

A

It is responsible for the accuracy and timing of the converter when converting A/D or D/A

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6
Q

PCM

A

Pulse Code Modulation

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7
Q

PCM’s two basic properties that determine quality of recorded audio

A
  1. Sample rate

2. Bit depth

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8
Q

Sample rate

A

Determines frequency response

How many samples per second per track

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9
Q

Bit depth

A

Determines dynamic range and resolution (volume)
Deals with amount of information happening
Amount of bits stored for every sample take

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10
Q

Samples

A

Samples are snapshots of information throughout bit depth (volume/level) fluctuates over sample rate (time)
The more snapshots, the more samples

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11
Q

Main function of an audio interface

A

Converts analog signal to digital (binary) information

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12
Q

Analog sound pressure waves representation

A

AC voltage (positive & negative charges) on a molecular level

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13
Q

Digital sound pressure waves representation

A

Binary information

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14
Q

Analog/Digital: Which has the more accurate representation of sound/waveform?

A

Analog

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15
Q

List at least 3 advantages of digital audio

A
  1. Non-destructive editing
  2. Visual editing
  3. Recall sessions
  4. Flexibility in sharing
  5. Portability in equipment
  6. Affordability
  7. Maintenance (DAWs and plug-ins have no wear&tear)
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16
Q

Information in between samples

A

Information in between samples are lost

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17
Q

Dynamic resolution formula

A

2^n = same as calculating bit in a binary word

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18
Q

Quantisation

A

The sample’s level is quantised to the nearest value based on the bit depth

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19
Q

Nyquist theorem

A

The sample rate must be at least 2x the highest audio frequency being recorded or converted
The highest frequency you can capture is half the sample rate

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20
Q

Nyquist theorem requires

A

At least one sample of both compression and rarefaction - if the frequency’s compressions and rarefactions are happening faster than the sample rate, it will not be captured correctly

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21
Q

Alias/Artefacts

A

These can be caused when the frequencies are higher than the sample rate

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22
Q

How do you get rid of alias/artefacts?

A

Anti-alias filter

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23
Q

Anti-alias filter

A

Steep low-pass filter at the Nyquist frequency which will cut off any higher frequencies

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24
Q

Standard CD quality sample rate and bit depth

A

44.1kHz sample rate

16 bit depth

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25
Q

From standard quality sample rate, how do you calculate the next common measurements?

A

Double the frequency

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26
Q

Next two common samples rates after 44.1kHz

A

Double 44.1 = 88.2kHz

Double 88.2 = 176.4kHz

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27
Q

Standard DVD quality sample rate and bit depth

A

48 kHz sample rate

24 bit depth

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28
Q

Next two common samples rates after 48kHz

A

Double 48 = 96kHz

Double 96 = 192kHz

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29
Q

BluRay quality sample rate and bit depth

A

192kHz

24 bit depth

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30
Q

Higher sample rate and bit depth essentially means

A

Less information is lost because we have more samples and information within each sample (bit depth)

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31
Q

How well can you hear a difference between these standard sample rates/bit depths?

A

Hardly any - human hearing only goes up to 20kHz. So this is more about information retention accuracy than being able to hear an actual difference

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32
Q

Up-sampling, and does it affect quality?

A

Up-sampling is only used for compatibility reasons, and it will NOT affect (or improve) quality
*can’t have more of what you already don’t have

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33
Q

Down-sampling, and does it affect quality?

A

We are now losing samples when we do this, therefore we will degrade the quality

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34
Q

Sample rate side effects

A

Jitter, phase issues, thin stereo image, drop outs, pops, clicks, etc.

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35
Q

Jitter

A

Digital TIMING error between samples

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36
Q

Bit depth formulas for Dynamic range and Dynamic resolution

A

Dynamic range: 1 bit = 6dB; n bits x 6dB = DR

Dynamic resolution: 2^n=degrees; n = bits

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37
Q

Bit depth=16

What is the dynamic range and dynamic resolution?

A

Dynamic range: 16 x 6 = 96dB

Dynamic resolution: 2^16 = 65,536 degrees

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38
Q

How often and how much is a simple way to describe these two things

A

Sample rate and bit depth

39
Q

Pro audio standard bit depth

40
Q

BluRay sample rate

41
Q

Compression ratio for .mp3

42
Q

Bit depth of audio CD

43
Q

Nyquist frequency of 48 kHz sample rate

44
Q

Degrees of dynamic resolution of 7 bit

A

128 degrees

45
Q

dBs of dynamic range of 16 bit

46
Q

Common bit rate for .mp3

47
Q

Quantisation noise

A

Q-noise: added noise from the converters working

48
Q

Higher bit depth affects Q-noise how?

A

Larger bit depth means larger dynamic range and resolution, pushing Q-noise further down to the bottom of the volume scale

49
Q

Quality that determines frequency response of a digital recording?

A

Sample rate

50
Q

Lossy vs lossless data compression

A

Lossless: non-destructive, temporary
Lossy: destructive, permanent

51
Q

Pro audio protocol for converting A/D & D/A

52
Q

iTunes bit rate

53
Q

ADAT channels

54
Q

Bit rate of CD quality uncompressed .wav file

55
Q

Consumer protocol for stereo digital audio

56
Q

Impedance of BNC cable

57
Q

Impedance of AES/EBU XLR cable

58
Q

Professional protocol for stereo digital audio

59
Q

Cable used in ADAT protocol

A

Toslink - fibre-optic cable

60
Q

Which protocol can use an RCA connector?

61
Q

Codec can be described as _____

62
Q

List the 3 AES/EBU connectors

A
  1. XLR
  2. BNC
  3. DB-25
63
Q

The Clock can be described as _____

A

A bit rate locking system, allowing multiple devices to move data at a controlled rate (sample rate)

64
Q

Embedding

A

The process of combining audio and video down a single cable

65
Q

Word clocks

A

Send out a pulse that has a timing reference (sample rate)

66
Q

Multiplexing

A

Combining multiple channels of audio down a single cable

67
Q

Advantage of using digital audio transfer protocols

A

It eliminates too many conversions from A/D or D/A

68
Q

Stereo digital audio protocol that uses a balanced cable with XLR connector

69
Q

Digital audio protocols that can use coaxial cable

A

AES, S/PDIF, MADI

70
Q

2 examples of lossless codecs

71
Q

3 examples of lossy codes

A

.mp3
.m4a
.ogg

72
Q

Is m4a lossy or lossless?

A

It can be either depending on how it’s encoded

AAC (lossy) or ALAC (lossless)

73
Q

2 examples of uncompressed audio files

A

.wav

.aiff

74
Q

Digital audio protocol that can send 64 channels

75
Q

S/PDIF connectors

A

Unbalanced 75Ω coaxial cable with RCA connector

Toslink fibre-optic cable

76
Q

List examples of multiplexing protocols

A 
AES/EBU
S/PDIF
ADAT
T/DIF
MADI
77
Q

3 advantages of Toslink fibre-optic cables

A
  1. No RFI (radio frequency interference)
  2. No EMI (electromagnetic interference)
  3. No ground loops
78
Q

Bit rate vs Bit depth

A

Bit rate: samples per second

Bit depth: how much/volume/dynamic range

79
Q

Master clock

A

One piece of gear that all the digital devices will lock in with for a timing reference

80
Q

Self-clocking

A

When a protocol can send clock information along with the audio it streams

81
Q

2 things used to “draw” a digital waveform

A
  1. Bit depth (how much)

2. Sample rate (how often)

82
Q

2 lowest common sample rates

A

44.1 kHz

48 kHz

83
Q

2 middle common sample rates

A

88.2 kHz

96 kHz

84
Q

2 highest common sample rates

A

176.4 kHz

192 kHz

85
Q

Bit rates unit of measurement

A

kilobits per second = kbps

86
Q

Highest bit rate for .mp3

87
Q

T/DIF channels

88
Q

Cable used in T/DIF protocol

89
Q

Cables used in MADI protocol

A

Unbalanced 75Ω coaxial cable with BNC connector

Fibre-optic cable with MADI optical connector

90
Q

Ogg Vorbis common bit rate

91
Q

Compression ratio for 560 kbps

92
Q

Highest quality lossy file type

93
Q

Compression ratio for 320 kbps

94
Q

Compression ratio for 256 kbps

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