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TM355 > B2P3 - Digitisation and lossy compression > Flashcards

B2P3 - Digitisation and lossy compression Flashcards

1
Q

a.c. coefficients

A

weights the basis functions at (1-7, 1-7) of a DCT table, the results evaluating to the amount of each spatial-frequency in the macroblock;

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2
Q

Adaptive Multi-Rate (AMR)

A

a speech coding standard that adapts its bit rate to channel conditions;

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3
Q

advanced audio coding (AAC)

A

MPEG-2/4 streamingFormat, with better quality than MP3 but with same bitRate;

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4
Q

aliasing

A

where samplingRate < 2*f;

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5
Q

analogue-to-digital converter (ADC)

A

takes an analogue signal, samples it, n-bit-quantises it, and returns a digital signal;

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6
Q

basis function

A

reps a specific hori-vert spatial-frequency, appearing as an entry in a DCT table;

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7
Q

B-frames

A

‘bi-directional prediction’ frames inserted between I-frames and P-frames filling in missing frames in the group of pictures (GOP) format;

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8
Q

bit rate

A

number of bits passing a given point in the network per unit time;

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9
Q

code-excited linear prediction (CELP)

A

= LPC - U/V_switch + codebook;

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10
Q

coding efficiency

A

minimising bitRate while holding videoQuality constant, or vice versa;

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11
Q

comfort noise (CN)

A

synthetic background noise for silent periods in voiceComms;

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12
Q

d.c. coefficient

A

weights the basis function at (0, 0) of a DCT table, the result evaluating to the average spatial-frequency of the whole macroblock;

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13
Q

dequantising

A

dequantise(n-bit_reps) = analogue;

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14
Q

difference error

A

pixel-subtracting one video frame from another;

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15
Q

difference pulse-code modulation (DPCM)

A

= PCM + predictionOfDataSamples (used in JPEG);

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16
Q

discontinuous transmission (DTX)

A

where mobile devices are powered-down when there is no voiceInput;

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17
Q

discrete cosine transformation (DCT)

A

DCT(spatialRep) = frequencyRep (used in J/MPEG);

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18
Q

discrete wavelet transform (DWT)

A

DWT(spatialRep) = frequencyRep (used in JPEG2000; better performance at low bitRates);

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19
Q

distortion

A

= reconstructedSignal - originalSignal;

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20
Q

encoding

A

encode(symbols) = bitStrings;

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21
Q

formants

A

the vocal tract’s spectral peaks characterising ‘voiced’ speechSegments;

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22
Q

frequency masking

A

where high-amplitude sounds cover up low-amplitude sounds at neighbouring frequencies;

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23
Q

group of pictures (GOP)

A

concatenating I-, P-, and B-frames for videoCompression (used in MPEG-1/2/4);

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24
Q

H.264 / advanced video coding (AVC)

A

an MPEG-4 videoCodingStreaming tech;

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25
Q

HE-AAC version 2

A

a tech optimised for low-bitRate audioStreaming apps including digi-radioBroadcasting;

26
Q

I-frames

A

‘intra-frames’ are real reps of world (i.e. they are not fillers nor predictions);

27
Q

inter-frame compression

A

stateful video compression;

28
Q

intra-frame compression

A

stateless video compression;

29
Q

inverse DCT

A

DCT_inv(frequencyRep) = spatialRep;

30
Q

Joint Photographic Experts Group (JPEG)

A

an lossy compression standard for images using DCT;

31
Q

linear predictive coding (LPC)

A

a sourceCoding method using parameters designed for speechSignals;

32
Q

low frequency effect (LFE / subwoofer)

A

where the channel delivers bass-only information (<120 Hz);

33
Q

macroblock

A

the formalParameter for the DCT() function, consisting of 8x8 pixels for JPEG and 16x16 pixels for MPEG;

34
Q

mask-to-noise ratio (MNR)

A

determines bits per sub-band in MP3 using psychoacoustic model;

35
Q

motion-JPEG (M-JPEG)

A

stateless video compression;

36
Q

motion prediction

A

frame_n.macroblocks = frame_n-1.macroblocks + motionVectors;

37
Q

motion vectors (MVs)

A

used in MPEG video coding to predict camera and object motion;

38
Q

MPEG audio layer 3 (MP3)

A

a compressed audio file format;

39
Q

noise masking

A

= frequency masking, temporal masking, and perceptual masking;

40
Q

Ogg Vorbis (OV)

A

an open-source lossy audio compression format;

41
Q

perceptual noise substitution (PNS)

A

where real noise is replaced with randomly generated noise;

42
Q

perceptual redundancy

A

where sounds / images are irrelevant as humans do not perceive them;

43
Q

P-frames

A

‘prediction-frames’ do not rep the world and instead are an educated guess based on the previous I-frame;

44
Q

prediction (residual) error

A

= P-frame(t)* - I-frame(t);

*based on I-frame(t-1);

45
Q

pulse code modulation (PCM)

A

PCM(analogueSignal) = encoding ( quantising ( sampling ( analogueSignal ) ) ) = digitalSignal;

46
Q

quality of service (QoS)

A

QoS(network) = minThoughput / maxLatency / lowestBER;

47
Q

quantisation noise (quantisation error)

A

= analogueSignal - digitalSignal;

48
Q

quantisation (quantising)

A

n-bit-quantise(sample(analogueSignal)) = digitalSignal;

49
Q

rate-distortion (RD) curves

A

bitsPerSymbol plotted against distortionError;

50
Q

region-of-interest (ROI) coding

A

where different areas of an image are coded at different bitRates (used in JPEG2000);

51
Q

resolution

A

bitsPerSymbol;

52
Q

sampling

A

measuring an analogueSignal at regular intervals;

53
Q

sampling theorem

A

IF (samplingRate >= 2*f) THEN (signal can be reconstructed);

54
Q

scalabililty (subsets)

A

where video/audio compression has subsets of varying bitsPerSymbol;

55
Q

statistical redundancy

A

where repeating patterns are identified and repped with a symbol;

56
Q

temporal masking

A

where a high-amplitude sound covers up a subsequent low-amplitude sound;

57
Q

thresholding

A

setting a constant such that any values lower than this can be ignored;

58
Q

unvoiced sounds

A

where there are no formants; can be repped by Gaussian noise;

59
Q

vocoder

A

portmanteau of ‘voice’ and ‘encoder’; compresses speech;

60
Q

voiced sounds

A

where there are formants;

TM355 (10 decks)

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