MPEG- -1 1 MPEG Overview of MPEG- -1 Standard 1 Standard Overview of MPEG Introduction to perceptual and entropy codings codings Introduction to perceptual and entropy
Contents Contents History History Psychoacoustics and perceptual coding Psychoacoustics and perceptual coding Entropy coding Entropy coding MPEG- -1 1 MPEG Layer I/II Layer I/II Layer III (MP3) Layer III (MP3) Comparison and Audio Quality Comparison and Audio Quality 25 September 2009 MPEG- -1 Presentation 1 Presentation 2 25 September 2009 MPEG 2
Introduction Introduction Digitizing an analog signal is (lossy lossy) compression ) compression Digitizing an analog signal is ( Digitizing introduces quantization noise Digitizing introduces quantization noise Quantization noise imply loss of quality Quantization noise imply loss of quality inaudible noise (CD) Linear quantization > 16 bit (98 dB) inaudible noise (CD) Linear quantization > 16 bit (98 dB) Linear quantization 4 bit (26 dB) Linear quantization 4 bit (26 dB) 25 September 2009 MPEG- -1 Presentation 1 Presentation 3 25 September 2009 MPEG 3
Contents Contents History History Psychoacoustics and perceptual coding Psychoacoustics and perceptual coding Entropy coding Entropy coding MPEG- -1 1 MPEG Layer I/II Layer I/II Layer III (MP3) Layer III (MP3) Comparison and Audio Quality Comparison and Audio Quality 25 September 2009 MPEG- -1 Presentation 1 Presentation 4 25 September 2009 MPEG 4
History History Moving Picture Expert Group (MPEG) Moving Picture Expert Group (MPEG) Created in January 1988 Created in January 1988 Starts the development of MPEG- -1 in May 1988 1 in May 1988 Starts the development of MPEG Publishes the MPEG- -1 standard in November 1992 (ISO/IEC 11172 1 standard in November 1992 (ISO/IEC 11172- - Publishes the MPEG 3 for audio) 3 for audio) MPEG- -1 standard 1 standard MPEG Defines bit- -stream stream Defines bit Defines decoding functions Defines decoding functions DOES NOT define encoding techniques DOES NOT define encoding techniques Inspired by MUSICAM (Masking pattern Universal Subband Integrated Coding And Multiplexing) ) 25 September 2009 MPEG- -1 Presentation 1 Presentation 5 25 September 2009 MPEG 5
Contents Contents History History Psychoacoustics and perceptual coding Psychoacoustics and perceptual coding Entropy coding Entropy coding MPEG- -1 1 MPEG Layer I/II Layer I/II Layer III (MP3) Layer III (MP3) Comparison and Audio Quality Comparison and Audio Quality 25 September 2009 MPEG- -1 Presentation 1 Presentation 6 25 September 2009 MPEG 6
Psychoacoustics Psychoacoustics Masking effect Masking effect Time domain masking ( Pohlmann 2000 ) Frequency domain masking ( Pohlmann 2000 ) Critical bands Critical bands higher central z/Bark lower boundary boundary bandwidth 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 Idealized critical bands ( Painter & Spanias ( Brandenburg ) 2000 ) 25 September 2009 MPEG- -1 Presentation 1 Presentation 7 25 September 2009 MPEG 7
Perceptual Coding Perceptual Coding Dividing the different subbands subbands Dividing the different of a signal of a signal Ignoring masked audio Ignoring masked audio Bits association according to masking threshold ( Pohlmann 2000 ) information information Introducing inaudible Introducing inaudible quantization noise quantization noise Quantization noise added according to masking threshold ( Pohlmann 2000 ) 25 September 2009 MPEG- -1 Presentation 1 Presentation 8 25 September 2009 MPEG 8
Perceptual Coding Perceptual Coding Perceptual Encoder/Decoder ( Kahrs & Brandenburg 1998 ) 25 September 2009 MPEG- -1 Presentation 1 Presentation 9 25 September 2009 MPEG 9
Contents Contents History History Psychoacoustics and perceptual coding Psychoacoustics and perceptual coding Entropy coding Entropy coding MPEG- -1 1 MPEG Layer I/II Layer I/II Layer III (MP3) Layer III (MP3) Comparison and Audio Quality Comparison and Audio Quality 25 September 2009 MPEG- -1 Presentation 1 Presentation 10 25 September 2009 MPEG 10
Entropic Coding Entropic Coding Use information about the signal to code Use information about the signal to code efficiently efficiently Entropy of a signal Entropy of a signal Example 1: {0, 2, 2, 2, 0, 0, 0, 0, 0, 2, 0, 3, 2, 2, 0, 0, 0, 3, 0, 0} Example 1: {0, 2, 2, 2, 0, 0, 0, 0, 0, 2, 0, 3, 2, 2, 0, 0, 0, 3 , 0, 0} 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) 20 symbols Entropy H H = 1.30 = 1.30 Entropy Example 2: {1, 2, 3, 0, 2, 1, 1, 2, 3, 0, 0, 1, 0, 3, 3, 3, 2, 0, 1, 2} Example 2: {1, 2, 3, 0, 2, 1, 1, 2, 3, 0, 0, 1, 0, 3, 3, 3, 2, 0 , 1, 2} 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) 20 symbols Entropy H H = 2 = 2 Entropy Shannon theorem Shannon theorem It is impossible to code with less than It is impossible to code with less than H H bits/symbol bits/symbol It is possible to code with less than It is possible to code with less than H+ H+ 1 1 bits/symbol bits/symbol 25 September 2009 MPEG- -1 Presentation 1 Presentation 11 25 September 2009 MPEG 11
Entropic Coding Entropic Coding Huffman coding Huffman coding Example 1: {0, 2, 2, 2, 0, 0, 0, 0, 0, 2, 0, 3, 2, 2, 0, 0, 0, 3, 0, 0} , 0, 0} Example 1: {0, 2, 2, 2, 0, 0, 0, 0, 0, 2, 0, 3, 2, 2, 0, 0, 0, 3 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) 20 symbols Entropy H H = 1.30 = 1.30 Entropy Immediate coding: Immediate coding: “ “ “ “ 0 1 2 3 “00 00” ” “01 01” ” “10 10” ” “11 11” ” 0 1 2 3 “0010101000000000001000111010000000110000 0010101000000000001000111010000000110000” ” “ Huffman coding: Huffman coding: “ “ “ “ 0 1 2 3 “0 0” ” “111 111” ” “10 10” ” “110 110” ” 0 1 2 3 “010101000000100110101000011000 010101000000100110101000011000” ” “ Efficiency: Efficiency: Immediate coding: 2 bits/symbol Immediate coding: 2 bits/symbol Huffman coding: 1.5 bits/symbol (statistically) Huffman coding: 1.5 bits/symbol (statistically) 25 September 2009 MPEG- -1 Presentation 1 Presentation 12 25 September 2009 MPEG 12
Contents Contents History History Psychoacoustics and perceptual coding Psychoacoustics and perceptual coding Entropy coding Entropy coding MPEG- -1 1 MPEG Layer I/II Layer I/II Layer III (MP3) Layer III (MP3) Comparison and Audio Quality Comparison and Audio Quality 25 September 2009 MPEG- -1 Presentation 1 Presentation 13 25 September 2009 MPEG 13
MPEG- -1 1 MPEG Sampling rate: 32, 44.1 and 48 kHz Sampling rate: 32, 44.1 and 48 kHz Four modes: Four modes: Mono: 1 channel Mono: 1 channel Stereo: 2 channels Stereo: 2 channels Dual: 2 channels independent (e.g. bilingual programmes programmes) ) Dual: 2 channels independent (e.g. bilingual Joint stereo: 2 channels coded together Joint stereo: 2 channels coded together 2 perceptual models 2 perceptual models Floating point quantization (normalization) Floating point quantization (normalization) Error checking: Cyclic redundancy check (CRC) Error checking: 25 September 2009 MPEG- -1 Presentation 1 Presentation 14 25 September 2009 MPEG 14
Contents Contents History History Psychoacoustics and perceptual coding Psychoacoustics and perceptual coding Entropy coding Entropy coding MPEG- -1 1 MPEG Layer I/II Layer I/II Layer III (MP3) Layer III (MP3) Comparison and Audio Quality Comparison and Audio Quality 25 September 2009 MPEG- -1 Presentation 1 Presentation 15 25 September 2009 MPEG 15
MPEG- -1 Layer I 1 Layer I MPEG From 32 to 448 kbps From 32 to 448 kbps 32- -subband subband polyphase polyphase 32 filterbank filterbank Bit allocation (0- -15) 15) Bit allocation (0 Example of Layer I encoder ( Pohlmann 2000 ) Max dynamic range > 120 dB Max dynamic range > 120 dB Linear quantization Linear quantization Layer I frame format ( Pohlmann 2000 ) 384 samples 1 frame 384 samples 1 frame Example: Philips Digital Example: Philips Digital Compact Cassette Compact Cassette 25 September 2009 MPEG- -1 Presentation 1 Presentation 16 25 September 2009 MPEG 16
Recommend
More recommend
