MPEG-1 - McGill Schulich Faculty of Musicich/classes/mumt621_09/presentations... · 2011. 1. 2. ·...
Transcript of MPEG-1 - McGill Schulich Faculty of Musicich/classes/mumt621_09/presentations... · 2011. 1. 2. ·...
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MPEGMPEG--11
Overview of MPEGOverview of MPEG--1 Standard1 StandardIntroduction to perceptual and entropy Introduction to perceptual and entropy codingscodings
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ContentsContents
HistoryHistory
Psychoacoustics and perceptual codingPsychoacoustics and perceptual coding
Entropy codingEntropy coding
MPEGMPEG--11
Layer I/IILayer I/II
Layer III (MP3)Layer III (MP3)
Comparison and Audio QualityComparison and Audio Quality
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IntroductionIntroduction
Digitizing an analog signal is (Digitizing an analog signal is (lossylossy) compression) compression
Digitizing introduces quantization noiseDigitizing introduces quantization noise
Quantization noise imply loss of qualityQuantization noise imply loss of quality
Linear quantization > 16 bit (98 dB) Linear quantization > 16 bit (98 dB) inaudible noise (CD)inaudible noise (CD)
Linear quantization 4 bit (26 dB)Linear quantization 4 bit (26 dB)
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ContentsContents
HistoryHistory
Psychoacoustics and perceptual codingPsychoacoustics and perceptual coding
Entropy codingEntropy coding
MPEGMPEG--11
Layer I/IILayer I/II
Layer III (MP3)Layer III (MP3)
Comparison and Audio QualityComparison and Audio Quality
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HistoryHistory
Moving Picture Expert Group (MPEG)Moving Picture Expert Group (MPEG)
Created in January 1988Created in January 1988
Starts the development of MPEGStarts the development of MPEG--1 in May 19881 in May 1988
Publishes the MPEGPublishes the MPEG--1 standard in November 1992 (ISO/IEC 111721 standard in November 1992 (ISO/IEC 11172-- 3 for audio)3 for audio)
MPEGMPEG--1 standard1 standard
Defines bitDefines bit--streamstream
Defines decoding functionsDefines decoding functions
DOES NOT define encoding techniquesDOES NOT define encoding techniques
Inspired by MUSICAM (Masking pattern Universal Subband Integrated Coding And Multiplexing) )
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ContentsContents
HistoryHistory
Psychoacoustics and perceptual codingPsychoacoustics and perceptual coding
Entropy codingEntropy coding
MPEGMPEG--11
Layer I/IILayer I/II
Layer III (MP3)Layer III (MP3)
Comparison and Audio QualityComparison and Audio Quality
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PsychoacousticsPsychoacoustics
Masking effectMasking effect
Critical bandsCritical bandsz/Bark lower boundary
higher boundary bandwidth
central frequency
0 0 100 100 50
1 100 200 100 150
2 200 300 100 250
3 300 400 100 350
4 400 510 110 450
5 510 630 120 570
6 630 770 140 700
7 770 920 150 840
(Brandenburg)
Time domain masking (Pohlmann 2000) Frequency domain masking (Pohlmann 2000)
Idealized critical bands (Painter & Spanias 2000)
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Perceptual CodingPerceptual Coding
Dividing the different Dividing the different subbandssubbandsof a signalof a signal
Ignoring masked audio Ignoring masked audio informationinformation
Introducing inaudibleIntroducing inaudiblequantization noisequantization noise
Bits association according to masking threshold (Pohlmann 2000)
Quantization noise added according to masking threshold (Pohlmann 2000)
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Perceptual CodingPerceptual Coding
Perceptual Encoder/Decoder (Kahrs & Brandenburg 1998)
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ContentsContents
HistoryHistory
Psychoacoustics and perceptual codingPsychoacoustics and perceptual coding
Entropy codingEntropy coding
MPEGMPEG--11
Layer I/IILayer I/II
Layer III (MP3)Layer III (MP3)
Comparison and Audio QualityComparison and Audio Quality
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Entropic CodingEntropic Coding
Use information about the signal to code Use information about the signal to code efficientlyefficiently
Entropy of a signalEntropy of a signal
Example 1: {0, 2, 2, 2, 0, 0, 0, 0, 0, 2, 0, 3, 2, 2, 0, 0, 0, 3Example 1: {0, 2, 2, 2, 0, 0, 0, 0, 0, 2, 0, 3, 2, 2, 0, 0, 0, 3, 0, 0}, 0, 0}20 symbols 20 symbols –– twelve 0 (0.6), zero 1 (0), six 2 (0.3), two 3 (0.1)twelve 0 (0.6), zero 1 (0), six 2 (0.3), two 3 (0.1)Entropy Entropy H H = 1.30= 1.30
Example 2: {1, 2, 3, 0, 2, 1, 1, 2, 3, 0, 0, 1, 0, 3, 3, 3, 2, 0Example 2: {1, 2, 3, 0, 2, 1, 1, 2, 3, 0, 0, 1, 0, 3, 3, 3, 2, 0, 1, 2}, 1, 2}20 symbols 20 symbols –– five 0 (0.25), five 1 (0.25), five 2 (0.25), five 3 (0.25)five 0 (0.25), five 1 (0.25), five 2 (0.25), five 3 (0.25)Entropy Entropy H H = 2= 2
Shannon theoremShannon theorem It is impossible to code with less than It is impossible to code with less than H H bits/symbolbits/symbol It is possible to code with less than It is possible to code with less than H+H+11 bits/symbolbits/symbol
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Entropic CodingEntropic Coding
Huffman codingHuffman coding
Example 1: {0, 2, 2, 2, 0, 0, 0, 0, 0, 2, 0, 3, 2, 2, 0, 0, 0, 3Example 1: {0, 2, 2, 2, 0, 0, 0, 0, 0, 2, 0, 3, 2, 2, 0, 0, 0, 3, 0, 0}, 0, 0}20 symbols 20 symbols –– twelve 0 (0.6), zero 1 (0), six 2 (0.3), two 3 (0.1)twelve 0 (0.6), zero 1 (0), six 2 (0.3), two 3 (0.1)Entropy Entropy H H = 1.30= 1.30
Immediate coding:Immediate coding:0 0 ““0000”” 1 1 ““0101”” 2 2 ““1010”” 3 3 ““1111””““00101010000000000010001110100000001100000010101000000000001000111010000000110000””
Huffman coding:Huffman coding:0 0 ““00”” 1 1 ““111111”” 2 2 ““1010”” 3 3 ““110110””
““010101000000100110101000011000010101000000100110101000011000””
Efficiency:Efficiency:
Immediate coding: 2 bits/symbolImmediate coding: 2 bits/symbol
Huffman coding: 1.5 bits/symbol (statistically)Huffman coding: 1.5 bits/symbol (statistically)
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ContentsContents
HistoryHistory
Psychoacoustics and perceptual codingPsychoacoustics and perceptual coding
Entropy codingEntropy coding
MPEGMPEG--11
Layer I/IILayer I/II
Layer III (MP3)Layer III (MP3)
Comparison and Audio QualityComparison and Audio Quality
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MPEGMPEG--11
Sampling rate: 32, 44.1 and 48 kHzSampling rate: 32, 44.1 and 48 kHz
Four modes:Four modes:
Mono: 1 channelMono: 1 channel
Stereo: 2 channelsStereo: 2 channels
Dual: 2 channels independent (e.g. bilingual Dual: 2 channels independent (e.g. bilingual programmesprogrammes))
Joint stereo: 2 channels coded togetherJoint stereo: 2 channels coded together
2 perceptual models2 perceptual models
Floating point quantization (normalization)Floating point quantization (normalization)
Error checking: Error checking: Cyclic redundancy check (CRC)
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ContentsContents
HistoryHistory
Psychoacoustics and perceptual codingPsychoacoustics and perceptual coding
Entropy codingEntropy coding
MPEGMPEG--11
Layer I/IILayer I/II
Layer III (MP3)Layer III (MP3)
Comparison and Audio QualityComparison and Audio Quality
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MPEGMPEG--1 Layer I1 Layer I
From 32 to 448 kbpsFrom 32 to 448 kbps
3232--subband subband polyphasepolyphasefilterbankfilterbank
Bit allocation (0Bit allocation (0--15)15)
Max dynamic range > 120 dBMax dynamic range > 120 dB
Linear quantizationLinear quantization
1 frame 1 frame 384 samples384 samplesExample: Philips DigitalExample: Philips DigitalCompact CassetteCompact Cassette
Example of Layer I encoder (Pohlmann 2000)
Layer I frame format (Pohlmann 2000)
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MPEGMPEG--1 Layer II1 Layer II
From 32 to 384 kbpsFrom 32 to 384 kbps
Improvement of Layer IImprovement of Layer I
Improved FFT analysisImproved FFT analysis
Scale factor redundancyScale factor redundancy
Finer quantizationFiner quantization
1 frame 1 frame 1152 samples1152 samples
Example: Digital Audio Example: Digital Audio Broadcasting (DAB)Broadcasting (DAB)
Example of Layer II encoder (Pohlmann 2000)
Layer II frame format (Pohlmann 2000)
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ContentsContents
HistoryHistory
Psychoacoustics and perceptual codingPsychoacoustics and perceptual coding
Entropy codingEntropy coding
MPEGMPEG--11
Layer I/IILayer I/II
Layer III (MP3)Layer III (MP3)
Comparison and Audio QualityComparison and Audio Quality
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MPEGMPEG--1 Layer III (MP3)1 Layer III (MP3)
From 32 to 320 kbpsFrom 32 to 320 kbps
Improvements:Improvements:
Finer psychoacoustics modelFiner psychoacoustics model
Alias reduction (MDCT filters)Alias reduction (MDCT filters)
NonuniformNonuniform quantizationquantization
Entropy codingEntropy coding
AdaptativeAdaptative block sizeblock size
Only Layer with patentsOnly Layer with patents
Inspired by:Inspired by:
ASPEC (audio spectral perceptualentropy coding)
OCF (optimal coding in the freq. domain)
Example of Layer III encoder (Pohlmann 2000)
Layer III frame format (Pohlmann 2000)
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MPEGMPEG--1 Layer III (MP3)1 Layer III (MP3)
Filtering: Hybrid Filtering: Hybrid polyphasepolyphase filter/MDCTfilter/MDCT
SteadySteady--state signals: 18state signals: 18--point MDCT on every point MDCT on every subbandsubbandFrequency resolution: 41.67 HzFrequency resolution: 41.67 HzTime resolution: 24 msTime resolution: 24 ms
Transient signals: 6Transient signals: 6--point MDCTpoint MDCTFrequency resolution: 125 HzFrequency resolution: 125 HzTime resolution: 8 msTime resolution: 8 ms
3 blocks modes3 blocks modes
PrePre--echo detectionecho detection
Quantization : power 3/4Quantization : power 3/4
Entropy coding: Entropy coding:
Huffman tablesHuffman tables
Run length codingRun length coding
Filtering stage in Layer III encoder (Pohlmann 2000)
MDCT filterbank in Layer III encoder (Pohlmann 2000)
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Joint Stereo CodingJoint Stereo Coding
Intensity codingIntensity coding
Sum of left/right channelsSum of left/right channels
Coding of the sum and of left/right scale factorsCoding of the sum and of left/right scale factors
Usually only for highUsually only for high--frequency frequency subbandssubbands
Efficient for redundant audio channelsEfficient for redundant audio channels
MS (mid/side) stereo codingMS (mid/side) stereo coding
Sum and difference of left/right channelsSum and difference of left/right channels
Coding of the two valuesCoding of the two values
Stereo maskingStereo masking
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ContentsContents
HistoryHistory
Psychoacoustics and perceptual codingPsychoacoustics and perceptual coding
Entropy codingEntropy coding
MPEGMPEG--11
Layer I/IILayer I/II
Layer III (MP3)Layer III (MP3)
Comparison and Audio QualityComparison and Audio Quality
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Audio QualityAudio Quality
Comparison with CDComparison with CD--quality at 48 kHz (16 bit quality at 48 kHz (16 bit -- 1.412 Mbps)1.412 Mbps)
Layer I: Layer I:
No perceptual difference for 384 kbps (stereo) No perceptual difference for 384 kbps (stereo) –– 2:1 compression2:1 compression
Layer II:Layer II:
No perceptual difference for 256 kbps (stereo) No perceptual difference for 256 kbps (stereo) –– 4:1 compression4:1 compression
Layer IIILayer III
Increase of mean opinion score compared to Layer II at 256 kbps Increase of mean opinion score compared to Layer II at 256 kbps (stereo) for 128 kbps (stereo) (stereo) for 128 kbps (stereo) –– 8:1 compression8:1 compression
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Comparison between LayersComparison between Layers
Layers I and II are very similarLayers I and II are very similar
Each Layer has its defined decoder design Each Layer has its defined decoder design
Encoding/Decoding complexity: Layer I/IIEncoding/Decoding complexity: Layer I/II broadcastingbroadcasting
Encoding/Decoding quality: Layer IIIEncoding/Decoding quality: Layer III audio storageaudio storage
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ConclusionConclusion
BibliographyBibliography::
AmbikairajahAmbikairajah, E. & al. , E. & al. Auditory masking and MPEGAuditory masking and MPEG--1 audio compression1 audio compression, , Electronics & Communication Engineering Journal, Electronics & Communication Engineering Journal, 19971997
Brandenburg, K. & Brandenburg, K. & BosiBosi, M. , M. Overview of MPEG Audio: Current and Future Overview of MPEG Audio: Current and Future Standards for LowStandards for Low--BitBit--Rate Audio CodingRate Audio Coding, Journal of the Audio Engineering Society, , Journal of the Audio Engineering Society, 19971997, Vol. Vol. 45(No. 1/2) , Vol. Vol. 45(No. 1/2)
Painter, T. & Painter, T. & SpaniasSpanias, A. , A. Perceptual Coding of Digital AudioPerceptual Coding of Digital Audio, Proceedings of IEEE, Proceedings of IEEE, , 20002000, Vol. Vol. 88(No. 4), Vol. Vol. 88(No. 4)
Painter, T. & Painter, T. & SpaniasSpanias, A. , A. A Review of Algorithms for Perceptual Coding of Digital A Review of Algorithms for Perceptual Coding of Digital Audio SignalsAudio Signals,, Digital SignalDigital Signal Processing, Processing, 19971997
Pan, D. Pan, D. A Tutorial on MPEG/Audio CompressionA Tutorial on MPEG/Audio Compression, IEEE , IEEE MultiMediaMultiMedia, IEEE , IEEE Computer Society, Computer Society, 19951995, Vol. 2(2), pp. 60, Vol. 2(2), pp. 60--7474
Pan, D.Y. Pan, D.Y. Digital Audio CompressionDigital Audio Compression, Digital Technical Journal, , Digital Technical Journal, 19931993, Vol. 5, Vol. 5
KahrsKahrs, M. and Brandenburg, K. , M. and Brandenburg, K. Applications of digital signal processing to audio Applications of digital signal processing to audio and acousticsand acoustics, , KluwerKluwer Academic Publishers, Academic Publishers, 19981998
MallatMallat, S. , S. TraitementTraitement du Signaldu Signal, , EcoleEcole Polytechnique, Polytechnique, 20002000
PohlmannPohlmann, K.C. , K.C. Principles of Digital Audio,Principles of Digital Audio, McGrawMcGraw--Hill Professional, Hill Professional, 20002000
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MPEG-1ContentsIntroductionContentsHistoryContentsPsychoacousticsPerceptual CodingPerceptual CodingContentsEntropic CodingEntropic CodingContentsMPEG-1ContentsMPEG-1 Layer IMPEG-1 Layer IIContentsMPEG-1 Layer III (MP3)MPEG-1 Layer III (MP3)Joint Stereo CodingContentsAudio QualityComparison between LayersConclusion