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for sound is a popular example of mu-law encoding. Using 8-bit mu-law encoding would cut the per-channel bitrate of CD audio down to about 350 kbit/s, half the standard rate. Because this simple method only minimally exploits masking effects, it produces results that are often audibly inferior
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First, a digital filter bank divides the input signal spectrum into some number (e.g., 32) of subbands. The psychoacoustic model looks at the energy in each of these subbands, as well as in the original signal, and computes masking thresholds using psychoacoustic information. Each of the subband
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The basic idea of SBC is to enable a data reduction by discarding information about frequencies which are masked. The result differs from the original signal, but if the discarded information is chosen carefully, the difference will not be noticeable, or more importantly, objectionable.
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samples is quantized and encoded so as to keep the quantization noise below the dynamically computed masking threshold. The final step is to format all these quantized samples into groups of data called frames, to facilitate eventual playback by a decoder.
237:. Human ears are normally sensitive to a wide range of frequencies, but when a sufficiently loud signal is present at one frequency, the ear will not hear weaker signals at nearby frequencies. We say that the louder signal masks the softer ones.
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may be thought of as a type of noise, because they are effectively the difference between the original source and its binary representation. With PCM, the audible effects of these errors can be mitigated with
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Decoding is much easier than encoding, since no psychoacoustic model is involved. The frames are unpacked, subband samples are decoded, and a frequency-time mapping reconstructs an output audio signal.
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and by using enough bits to ensure that the noise is low enough to be masked either by the signal itself or by other sources of noise. A high quality signal is possible, but at the cost of a high
276:) within a bit rate of 64 kbit/s. In the SB-ADPCM technique, the frequency band is split into two sub-bands (higher and lower) and the signals in each sub-band are encoded using ADPCM.
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for one channel of CD audio). In effect, many bits are wasted in encoding masked portions of the signal because PCM makes no assumptions about how the human ear hears.
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216:. Small signals are digitized with finer granularity than are large ones; the effect is to add noise that is proportional to the signal strength. Sun's
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The more bits used to represent each sample, the finer the granularity in the digital representation, and thus the smaller the quantization error. Such
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261:(MPEG), developed standards for coding of both audio and video. Subband coding resides at the heart of the popular MP3 format (more properly known as
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recordings, and so on. Digitization transforms continuous signals into discrete ones by sampling a signal's amplitude at uniform intervals and
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Coding techniques reduce bitrate by exploiting known characteristics of the auditory system. A classic method is nonlinear PCM, such as the
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The utility of SBC is perhaps best illustrated with a specific example. When used for audio compression, SBC exploits
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This article is about the signal coding technique. For the
Bluetooth audio codec, see
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codec which uses sub-band adaptive differential pulse code modulation (SB-
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175:. This process is fundamentally inexact, and involves two errors:
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Beginning in the late 1980s, a standardization body, the
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to the nearest value representable with the available
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The simplest way to digitally encode audio signals is
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128:that breaks a signal into a number of different
108:Sub-band coding and decoding signal flow diagram
61:but its sources remain unclear because it lacks
139:SBC is the core technique used in many popular
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92:Learn how and when to remove this message
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182:from sampling at intervals, and
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268:Sub-band coding is used in the
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259:Moving Picture Experts Group
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1368:Compressed data structures
690:RLE + BWT + MTF + Huffman
358:Asymmetric numeral systems
221:compared to the original.
26:
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727:Discrete cosine transform
657:LZ77 + Huffman + context
1432:Smallest grammar problem
286:Sub-Band Coding Tutorial
159:(PCM), which is used on
47:This article includes a
1373:Compressed suffix array
922:Nyquist–Shannon theorem
141:lossy audio compression
132:, typically by using a
76:more precise citations.
263:MPEG-1 Audio Layer III
151:Encoding audio signals
134:fast Fourier transform
109:
1402:Kolmogorov complexity
1270:Video characteristics
647:LZ77 + Huffman + ANS
157:pulse-code modulation
143:algorithms including
107:
1492:Compression software
1086:Compression artifact
1042:Psychoacoustic model
178:discretization error
1482:Compression formats
1121:Texture compression
1116:Standard test image
932:Silence compression
194:quantization errors
1390:Information theory
1245:Display resolution
1071:Chroma subsampling
460:Byte pair encoding
405:Shannon–Fano–Elias
185:quantization error
110:
49:list of references
1528:Signal processing
1523:Audio engineering
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1304:Deblocking filter
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124:) is any form of
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16:(Redirected from
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1091:Image resolution
1076:Coding tree unit
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322:Data compression
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265:), for example.
231:auditory masking
225:Basic principles
205:(e.g., over 700
126:transform coding
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72:this article by
63:inline citations
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780:Predictive type
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667:LZSS + Huffman
617:LZ77 + Huffman
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452:Dictionary type
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348:Adaptive coding
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235:auditory system
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214:ÎĽ-law algorithm
189:from rounding.
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130:frequency bands
118:sub-band coding
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53:related reading
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1448:Hutter Prize
1412:Quantization
1317:Compensation
1111:Quantization
946:
834:Compensation
400:Shannon–Fano
340:Entropy type
267:
256:
253:Applications
247:
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121:
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82:October 2011
79:
68:Please help
60:
1407:Prefix code
1260:Frame types
1081:Color space
907:Convolution
637:LZ77 + ANS
548:Incremental
521:Other types
440:Levenshtein
74:introducing
29:SBC (codec)
1512:Categories
1464:Mark Adler
1422:Redundancy
1339:Daubechies
1322:Estimation
1255:Frame rate
1177:Daubechies
1137:Chain code
1096:Macroblock
902:Companding
839:Estimation
759:Daubechies
465:Lempel–Ziv
425:Exp-Golomb
353:Arithmetic
1441:Community
1265:Interlace
651:Zstandard
430:Fibonacci
420:Universal
378:Canonical
161:audio CDs
1427:Symmetry
1395:Timeline
1378:FM-index
1223:Bit rate
1216:Concepts
1064:Concepts
927:Sampling
880:Bit rate
873:Concepts
575:Sequitur
410:Tunstall
383:Modified
373:Adaptive
331:Lossless
169:rounding
1385:Entropy
1334:Wavelet
1313:Motion
1172:Wavelet
1152:Fractal
1147:Deflate
1130:Methods
917:Latency
830:Motion
754:Wavelet
671:LHA/LZH
621:Deflate
570:Re-Pair
565:Grammar
395:Shannon
368:Huffman
324:methods
233:in the
203:bitrate
70:improve
1496:codecs
1457:People
1360:Theory
1327:Vector
844:Vector
661:Brotli
611:Hybrid
510:Snappy
363:Golomb
207:kbit/s
199:dither
1287:parts
1285:Codec
1250:Frame
1208:Video
1192:SPIHT
1101:Pixel
1056:Image
1010:ACELP
981:ADPCM
971:ÎĽ-law
966:A-law
959:parts
957:Codec
865:Audio
804:ACELP
792:ADPCM
769:SPIHT
710:Lossy
694:bzip2
685:LZHAM
641:LZFSE
543:Delta
435:Gamma
415:Unary
390:Range
274:ADPCM
270:G.722
55:, or
1299:DPCM
1106:PSNR
1037:MDCT
1030:WLPC
1015:CELP
976:DPCM
824:WLPC
809:CELP
787:DPCM
737:MDCT
681:LZMA
582:LDCT
560:DPCM
505:LZWL
495:LZSS
490:LZRW
480:LZJB
1344:DWT
1294:DCT
1238:VBR
1233:CBR
1228:ABR
1187:EZW
1182:DWT
1167:RLE
1157:KLT
1142:DCT
1025:LSP
1020:LAR
1005:LPC
998:FFT
895:VBR
890:CBR
885:ABR
819:LSP
814:LAR
799:LPC
764:DWT
749:FFT
744:DST
732:DCT
631:LZS
626:LZX
602:RLE
597:PPM
592:PAQ
587:MTF
555:DMC
533:CTW
528:BWT
500:LZW
485:LZO
475:LZ4
470:842
165:DAT
145:MP3
122:SBC
112:In
1514::
1162:LP
993:FT
986:DM
538:CM
163:,
147:.
116:,
59:,
51:,
1498:)
1494:(
314:e
307:t
300:v
187:,
180:,
120:(
95:)
89:(
84:)
80:(
66:.
31:.
20:)
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