INTERNATIONAL TELECOMMUNICATION UNION
`
`)45 4
`
`TELECOMMUNICATION
`STANDARDIZATION SECTOR
`OF ITU
`
`'
`
`'%.%2!,!30%#43/&$)')4!,42!.3-)33)/.
`3934%-3
`
`4%2-).!,%15)0-%.43
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`05,3%#/$%-/$5,!4)/.0#- /&
`6/)#%&2%15%.#)%3
`
`)45 4Recommendation'
`
`(Extract from the "LUE"OOK)
`
`Apple 1023
`U.S. Pat. 7,535,890
`
`I
`
`

`
`NOTES
`
`ITU-T Recommendation G.711 was published in Fascicle III.4 of the Blue Book. This file is an extract from
`1
`the Blue Book. While the presentation and layout of the text might be slightly different from the Blue Book version, the
`contents of the file are identical to the Blue Book version and copyright conditions remain unchanged (see below).
`
`In this Recommendation, the expression “Administration” is used for conciseness to indicate both a
`2
`telecommunication administration and a recognized operating agency.
`
`© ITU 1988, 1993
`
`All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or
`mechanical, including photocopying and microfilm, without permission in writing from the ITU.
`
`II
`
`

`
`Recommendation G.711
`
`Fascicle III.4 - Rec. G.711
`
`PULSE CODE MODULATION (PCM) OF VOICE FREQUENCIES
`
`(Geneva, 1972; further amended)
`
`1
`
`2
`
`General
`
`The characteristics given below are recommended for encoding voice-frequency signals.
`
`Sampling rate
`
`The nominal value recommended for the sampling rate is 8000 samples per second. The tolerance on that rate
`should be ± 50 parts per million (ppm).
`
`3
`
`3.1
`
`Encoding law
`
`Eight binary digits per sample should be used for international circuits.
`
`Two encoding laws are recommended and these are commonly referred to as the A-law and the μ-law. The
`3.2
`definition of these laws is given in Tables 1a/G.711 and 1b/G.711 and Tables 2a/G.711 and 2b/G.711 respectively.
`
`When using the μ-law in networks where suppression of the all 0 character signal is required, the character
`signal corresponding to negative input values between decision values numbers 127 and 128 should be 00000010 and
`the value at the decoder output is -7519. The corresponding decoder output value number is 125.
`
`3.3
`
`The number of quantized values results from the encoding law.
`
`Digital paths between countries which have adopted different encoding laws should carry signals encoded in
`3.4
`accordance with the A-law. Where both countries have adopted the same law, that law should be used on digital paths
`between them. Any necessary conversion will be done by the countries using the μ-law.
`
`3.5
`
`3.6
`
`The rules for conversion are given in Tables 3/G.711 and 4/G.711.
`
`Conversion to and from uniform PCM
`
`Every "decision value" and " quantized value" of the A (resp. μ) law should be associated with a "uniform
`PCM value". (For a definition of "decision value" and "quantized value", see Recommendation G.701 and in particular
`Figure 2/G.701). This requires the application of a 13 (14) bit uniform PCM code. The mapping from A-law PCM, and
`μ-law PCM, respectively, to the uniform code is given in Tables 1/G.711 and 2/G.711. The conversion to A-law or
`μ-law values from uniform PCM values corresponding to the decision values, is left to the individual equipment
`specification. One option is described in Recommendation G.721, § 4.2.8 subblock COMPRESS.
`
`4
`
`Transmission of character signals
`
`When character signals are transmitted serially, i.e. consecutively on one physical medium, bit No. 1 (polarity
`bit) is transmitted first and No. 8 (the least significant bit) last.
`
`Fascicle III.4 - Rec. G.711
`
`1
`
`

`
`5
`
`Relationship between the encoding laws and the audio level
`
`The relationship between the encoding laws of Tables 1/G.711 and 2/G.711 and the audio signal level is
`defined as follows:
`
`A sine-wave signal of 1 kHz at a nominal level of 0 dBm0 should be present at any voice frequency output of
`the PCM multiplex when the periodic sequence of character signals of Table 5/G.711 for the A-law and of
`Table 6/G.711 for the μ-law is applied to the decoder input.
`
`The resulting theoretical load capacity (Tmax) is +3.14 dBm0 for the A-law, and +3.17 dBm0 for the μ-law.
`Note - The use of another digital periodic sequence representing a nominal reference frequency of 1020 Hz at
`a nominal level of -10 dBm0 (preferred value, see Recommendation O.6) or 0 dBm0 is acceptable, provided that the
`theoretical accuracy of that sequence does not differ by more than ± 0.03 dB from a level of -10 dBm0 or 0 dBm0
`respectively. In accordance with Recommendation O.6, the specified frequency tolerance should be 1020 Hz + 2 Hz,
`-7 Hz.
`
`If a sequence representing -10 dBm0 is used, the nominal value at the voice frequency outputs should be
`-10 dBm0.
`
`2
`
`Fascicle III.4 - Rec. G.711
`
`

`
`TABLE 11110.7] 1
`A-law, positive input values
`
`
`
`
`1
`
`2
`
`3
`
`Segment
`number
`
`Number
`of intervals
`x interval
`-
`512°
`
`Value
`at segment
`end
`-
`t
`'”°"‘ 5
`
`-
`-
`DCCISIM
`Va “e
`number It
`
`Emir
`p
`Value
`number
`
`
`
`
`
`E§‘éZ‘~.£—Z°I§Z§i§IE.‘II
`-
`-
`ofthe even bits
`V31“
`Daemon
`(Value
`
`
`
`value X"
`.1
`d
`
`[see Note I)
`at
`°°° er
`as: number
`output) 2.
`
`I 2 3 4 5 6 T B
`
`
`
`
`
`[4096] — ~ — - - — — — — - — —
`I
`I
`l
`I
`I
`I
`I
`l
`3963 —--v-]——-
`I
`I
`:
`I
`I
`{see Note 2)
`I
`I
`2l76
`
`I
`I 0 U 0 0
`
`I
`
`l
`
`I
`
`
`
`4096
`
`(I28)
`
`I2’?
`I
`I
`I
`I
`I
`I13
`
`llll
`I
`In
`
`961
`I
`81
`
`so
`I
`I
`65
`
`6«I
`I
`49
`
`48'
`I
`33
`
`32
`I
`I
`l
`I
`I
`I
`I
`I
`I
`I
`
`2048
`
`I024
`
`5|}!
`
`256
`
`I23
`
`64
`
`I6xl6
`
`16 x 3
`
`16 x 4
`
`32 x 2
`
`4
`
`3
`
`2
`
`I
`I
`
`
`
`
`-
`
`
`-
`4032
`I28
`I
`I
`I
`|
`I
`I
`I
`I
`I
`I
`I
`I
`2lI2
`H3
`I
`I
`I
`I
`I
`I
`I
`I
`I056
`97
`I
`I
`I
`I
`I
`1
`I
`I
`$28
`81
`I
`I
`I
`I
`5
`264
`
`2043'
`I
`1088
`
`I
`(see Note 2)
`J
`I 0 0 0 0 0
`
`1
`
`I
`
`I024;
`I
`(see 1716:: 2)
`I
`544 4I——Ij
`I
`I 0 I
`I} 0 0 0 —
`5:2 —I—,——I
`I
`I
`I
`(9eel‘|10te2l
`'
`212
`I 0 0 D 0 0 0
`
`I
`
`
`
`I
`
`I G I 0 0 0 O U
`
`I
`.
`I
`I
`(see Ifillote 2]
`I
`l
`I
`
`I 0 O 0 0 O 0 0
`
`254%
`I
`136
`
`128!
`I
`68
`
`64
`I
`I
`I
`I
`I
`I
`I
`I
`2
`
`0
`
`,
`I
`I
`I
`65
`I
`1
`
`I
`49
`
`I
`
`
`
`
`= 3.14 dBm0.
`Note I — 4096 normalized value units correspond to T
`Note‘ 2 — The character signals are obtained by §l'|Vel'lIl'I|;mI.¥Ie even bits of the signals of column 6. Before this inversion, the character
`signal corresponding to positive input values between two successive decision values numbered It and 11' + I (see column 4) is (128 4- :1}
`expressed as a binary number
`In _ I + X”
`Note 3 — The value at the decoder output is y,, -—~“T for n = I, ..., I21‘. I28.
`Note 4 - x In is a virtual decision value.
`Note 5 — In Tables '.lfG.71l and 2/G.7ll the values of the uniform code are given in columns 3, S and T.
`
`Fascicle l]1.4 - Rec. G.711
`Fascicle III.4 - Rec. G.711
`
`3
`3
`
`

`
`TABLE lb I’G.'I"I1
`
`A-law. negative input values
`
`Segment
`Numb”
`
`
`Number
`Value
`Decision
`
`
`
`of Intervals
`at segment
`value
`x lggewal
`cI':Ls
`number :1
`90
`
`Decision
`value t
`(see l\EoIen|} I
`
`Character signal
`before ’nve
`'
`of the :.~ven'stIII:
`
`Bit number
`I 2 3 4 S 6 3' 3
`
`Quantixed
`vglug
`[value
`I at decoder
`output} )5.
`
`Decoder
`output
`Value
`
`
`I
`I
`
`2
`
`3
`
`4
`
`5
`
`32 " 2
`
`16 x 4
`
`'6 X 8
`
`I6 X I6
`
`“"32
`
`-54
`
`-I28
`
`-255
`
`-5|2
`
`-—|02-1
`
`-2048
`
`-4095
`
`I
`I
`I
`I
`I
`I
`I
`I
`I
`I
`I
`32
`
`33f
`I
`I
`43
`
`49
`I
`I
`I
`54
`
`65
`I
`I
`
`I
`80
`
`El
`I
`I
`I
`96
`
`91
`I
`
`I
`
`I I2
`
`II3
`I
`I
`I
`I2?!
`(I28)
`
`
`
`—Io38 —~:—e——
`I
`I
`
`I
`
`-2048
`
`I
`
`(see Driote 2)
`
`0! I IOOUI} -
`
`I
`I
`
`I
`
`I
`|
`-ZIIZ
`
`—2l'l'IS
`I
`I
`I
`—396£I
`(-4096) _
`
`I
`
`I
`I
`I
`I
`I
`‘ 4°32
`
`f’_'_'_'_'_'_ '_l
`
`Note I — 4096 normalized value units conespond to Tm = 3.I-I dBm0.
`Note 2 — The character signals are obtained by inverting fie even bits of the signals of column 6. Before this inversion, the character
`signal corresponding to negative input values between two successive decision values numbered n and H + I
`(see column 4) is I:
`n -—
`:1
`expressed as a binary number.
`X
`I + x
`Note 3 — The value at the decoder output is y,, =i’ for I: : I.
`Note 4 ~ .1: 123 is a virtual decision value.
`
`I27, I28.
`
`Note 5 — In Tables lz’CI.'l'll and 2/G.7ll the values of the unifonn code are given in columns 3, 5 and 7.
`
`4
`
`Fascicle III.4 - Rec. G.711
`Fascicle III.4 - Rec. G.711
`
`
`
`
`0 0 0 0 0 0 0 G
`
`--2
`1
`I
`I
`I
`I
`I
`I
`I
`(see Note 2]
`I
`I
`I
`I
`I
`I
`I
`I
`I
`~64 —-—W—Ij-
`I} 0 1 0 0 0 0 G
`
`—
`
`I
`
`I
`|
`I
`I
`I
`I
`I
`I
`I
`I
`I
`I
`I
`I
`I
`I
`'
`I
`I
`I
`I
`.55
`
`—6B| fifi I
`I
`(see Note 2}
`I
`I
`I
`I
`-123
`.
`.I32
`I
`
`UOIIIJDOD-
`I
`[see Note 2]
`I
`
`UIUUODOO
`
`I
`
`{see Note 2)
`
`I
`
`I
`
`_] 36
`I
`I
`I
`-256
`
`_2-“I2
`I
`I
`
`I
`—5|2
`
`_—
`
`I
`I
`-264
`
`I
`
`I
`I
`-528
`
`OI0l0DflO-
`-544 —-———-T
`I
`I
`I
`I
`I
`(see Note 2)
`I
`I
`I
`I
`I
`-1024 —
`OIIOOOUO-—lUS6
`
`33
`
`I
`I
`I
`I
`49
`I
`I
`I
`I
`65
`I
`I
`
`I
`I
`
`Bi
`
`I
`I
`I
`I
`I
`9‘!
`
`I
`I
`
`I
`
`I
`I
`II3
`
`I
`I
`I
`I
`I
`'23
`
`

`
`TABLEAU 2a I (3.71 I
`
`,u-law, positive input values
`
`Character signal
`
`
`Bit number
`2 3 4 S 6 7 8
`
`I
`
`Q‘-lfififizcd
`Va ue
`(value
`at decodm.
`output) y,,
`
`Decoder
`output
`value
`number
`
`.
`.
`$131?“
`(see Notefln
`
`
`
`Segrnenl
`number
`
`Number
`of intervals
`x m_lenIa]
`5'15
`
`(3159) - - - - - - - - - - - -
`303I
`-
`1903 _ .
`I
`'
`I
`I
`[see Note 2]
`E
`I
`I
`4319 on I
`I U 0 0 I
`I
`1
`l —
`4[9I
`
`I
`4063
`I
`I
`I
`I
`:
`(see Note 2)
`:
`2143 TAT I
`I 0 0 I
`I
`I
`l
`I —
`2079
`
`
`
`3
`
`7
`
`3
`
`2
`
`'
`I j
`—
`
`I2’?
`.
`I
`I
`I
`I
`112
`I
`I
`It
`I
`96
`
`I
`I
`ll
`I
`80
`'
`I
`I
`I
`
`I
`I
`I
`I
`
`I
`I
`ll
`I
`3%
`I
`I
`I
`16.
`I
`:
`I
`I
`‘
`I
`0
`
`2015
`I
`I
`I
`1055
`
`991
`I
`I
`511
`
`479
`I
`I
`239
`
`223
`‘
`I
`I
`I03
`
`“I
`‘I
`as
`
`3]!
`I
`I
`I
`3
`I
`
`1
`(see Note 2)
`I
`
`I 0 l 0 I
`
`l
`
`1
`
`I
`
`I
`(see Pllote 2)
`
`I
`(see Note 2)
`I
`
`I
`I
`I
`I
`1023
`‘
`I
`II
`I
`
`I
`I
`I
`I
`
`I
`{see Note 2)
`I
`
`I
`I
`I
`I
`@ 99.
`.
`I
`[see 1\!I'oIc 2)
`I
`I
`@ 3%
`I
`I
`I
`I
`[see Note 2}
`I
`I
`'
`T 2
`T 0
`
`0 T
`
`Note I -— 8159 normalized value units correspond to Tm“ = 3.17 dBmD.
`Note 2 — The character signal corresponding to positive Input values between two successive decision values numbered 1'! and n + I
`(see column 4) is (255 - I1) expressed as a binary number.
`x” ‘xrw 1
`Note 3 — The value at the decoder output is yo = x0 = 0 for n = 0. and ya = if for I1 = I, 2. ..., I27.
`Note 4 - x .3. is a virtual decision value.
`Note 5 — In Tables l/G.‘.-‘ll and 2/G.'I'll the values of the unifonn oode are given in columns 3. 5 and 1'.
`
`Fascicle l]1.4 - Rec. G.711
`Fascicle III.4 - Rec. G.711
`
`5
`5
`
`

`
`TABLE 2b 7’ G.‘I'|l
`
`Iwlarr, negative input values
`
`Segment
`number
`
`Number
`of Intervals
`X "1-larval
`Sm:
`
`vaiue
`at segment
`“Id
`poms
`
`.
`.
`DEEIES“
`number 77
`
`.
`.
`E:Ii':'_::
`(see Note I)
`
`Character signal
`
`Bit. number
`2 3 4 5 0 7 3
`
`1
`
`Q““"'fiz°d
`value
`(value
`3'’ d‘‘''°°d“
`output) )I,.
`
`0 1
`0 I
`
`I
`I
`
`I
`l
`
`I
`I
`
`I
`I
`
`I
`1
`I 0
`
`.
`(see I~_l0te 2}
`
`0
`
`—;I
`I
`I
`I
`—33I
`I
`I
`I
`'
`.9sI
`I
`I
`I
`I
`.23:
`I
`
`I
`I
`I
`I
`6|
`I
`I
`I
`I
`I
`I
`I
`I
`'
`43'
`I
`
`I
`I
`
`3
`
`3
`
`4
`
`5
`
`I x I
`
`I5 X 2
`
`'5 " 4
`
`I6 " 8
`
`'5 * '5
`
`15 " 32
`
`I6 x 04
`
`7
`
`'6 "‘ I23
`
`“"255
`
`-3!
`
`-95
`
`-223
`
`-479
`
`-99!
`
`-2015
`
`4003
`
`0
`I
`
`I
`I
`16
`
`ITI
`I
`I
`32
`
`33
`I
`I
`I
`43
`
`49
`I
`I
`04
`
`as
`I
`I
`so
`
`31
`I
`I
`
`I
`96
`
`97
`I
`I
`I
`I12
`
`II3
`I
`I26
`
`0
`I
`
`'3:
`I
`
`—3I
`
`-35
`I
`I
`.95
`
`-I03
`I
`I
`I
`-223
`
`-239
`I
`I
`I
`-479
`
`-5II
`I
`I
`-991
`
`-1055
`I
`I
`
`I
`-20I5
`
`—3I43
`I
`I
`I
`-4053
`
`—-13|9
`I
`-7547
`
`0 ‘W9
`
`I27
`"33’
`
`-7903
`“'5” "
`
`I
`
`I
`
`—
`
`—
`
`0 I
`
`I
`
`I
`
`I 0 I
`I
`(see Note 2)
`I
`
`0 I 0 1
`
`I
`
`I
`
`I
`
`I
`(see Note 2)
`I
`
`0100IIII
`
`I
`(see Note 2)
`I
`
`I
`I
`I
`I
`I
`I
`I
`I
`495.
`‘I
`I
`I
`I
`I
`I
`I
`I
`I
`d “I
`I
`I
`I
`I
`I
`'
`
`I
`(see Note 2)
`I
`
`I
`I
`-2079
`I
`
`I
`I
`I
`'
`4191'
`I
`I
`I
`-7775
`
`-0031
`
`I
`(see Note 2)
`I
`
`0000IIII
`
`(see Note 2)
`00000001
`
`0 0 0 0 0 0 0
`
`O
`
`I
`I
`90
`I
`
`I
`I
`I
`'
`IIZI
`I
`I
`I
`I26
`
`Note I — SE59 rlonnalized value units correspond to Tm“ = 3.17 dBm0.
`Note 2 - The character signal corresponding to negative Input values between two successive decision values numbered :1 and In + I
`(see column 4) is (12? — I-I) expressed as a binary number for 71 = 0, I, l2'I.
`
`Note 3 — The value at the decoder output isyo= 2:0: 0 for n = 0. and 57,, =T for :7 = I, 2. ...I I2".-‘.
`Nate 4 - .1: In is a vinual decision value.
`Note 5 —-
`In Tables I/G311 and 2fG.?1l the values of the uniform code are given in columns 3. 5 and T.
`
`6
`
`Fascicle III.4 - Rec. G.711
`Fascicle III.4 - Rec. G.711
`
`

`
`TABLE 3/G.711
`
`μ-A conversion
`
`μ-law
`
`Decoder output
`value number
`
`A-law
`
`Decoder output
`value number
`
`μ-law
`
`Decoder output
`value number
`
`A-law
`
`Decoder output
`value number
`
`41
`42
`43
`44
`46
`48
`49
`50
`51
`52
`53
`54
`55
`56
`57
`58
`59
`60
`61
`62
`64
`65
`66
`67
`68
`69
`70
`71
`72
`73
`74
`75
`76
`77
`78
`79
`81
`82
`83
`84
`85
`86
`87
`88
`
`...
`
`128
`
`44
`45
`46
`47
`48
`49
`50
`51
`52
`53
`54
`55
`56
`57
`58
`59
`60
`61
`62
`63
`64
`65
`66
`67
`68
`69
`70
`71
`72
`73
`74
`75
`76
`77
`78
`79
`80
`81
`82
`83
`84
`85
`86
`87
`
`...
`
`127
`
`11223344556677889
`
`10
`11
`12
`13
`14
`15
`16
`17
`18
`19
`20
`21
`22
`23
`24
`25
`27
`29
`31
`33
`34
`35
`36
`37
`38
`39
`40
`
`0123456789
`
`10
`11
`12
`13
`14
`15
`16
`17
`18
`19
`20
`21
`22
`23
`24
`25
`26
`27
`28
`29
`30
`31
`32
`33
`34
`35
`36
`37
`38
`39
`40
`41
`42
`43
`
`Notes relative to Table 3/G.711
`
`Note 1 - The input signals to an A-law decoder will normally include even bit inversion as applied in accordance with Note 2 of
`Table 1a/G.711. Consequently the output signals from a μ-A converter should have even bit inversion embodied within the converter
`output.
`
`Fascicle III.4 - Rec. G.711
`
`7
`
`

`
`Note 2 - If a μ-A conversion is followed by an A-μ conversion, most of the octets are restored to their original values. Only those
`octets which correspond to μ-law decoder output value numbers 0, 2, 4, 6, 8, 10, 12, 14 are changed (the numbers being increased by
`1). Moreover, in these octets, only bit No. 8 (least significant bit in PCM) is changed. Accordingly, the double conversion
`μ-A-μ is transparent to bits Nos. 1-7.
`
`Similarly, if an A-μ conversion is followed by a μ-A conversion, only the octets corresponding to A-law decoder output value
`numbers 26, 28, 30, 32, 45, 47, 63 and 80 are changed. Again, only bit No. 8 is changed, i.e. the double conversion A-μ-A, too, is
`transparent to bits No. 1-7.
`
`A consequence of this property is that in most of the analogue voice frequency signal range the additional quantizing distortion
`caused by μ-A-μ or A-μ-A conversion is considerably lower than that caused by either μ-A or A-μ conversion (see Recommendation
`G.113).
`
`The A-μ-A transparency for bits 1 to 7 was achieved by modifying the table slightly from the optimum conversion in that μ-80 is
`converted to A-81 instead of A-80, and A-80 is converted to μ-79 instead of μ-80. This has an insignificant effect on quantizing
`distortion.
`
`8
`
`Fascicle III.4 - Rec. G.711
`
`

`
`TABLE 4/G.711
`
`μ-A conversion
`
`A-law
`
`Decoder output
`value number
`
`μ-law
`
`Decoder output
`value number
`
`A-law
`
`Decoder output
`value number
`
`μ-law
`
`Decoder output
`value number
`
`52
`53
`54
`55
`56
`57
`58
`59
`60
`61
`62
`63
`64
`64
`65
`66
`67
`68
`69
`70
`71
`72
`73
`74
`75
`76
`77
`78
`79
`79
`80
`81
`82
`83
`84
`85
`86
`87
`88
`89
`90
`91
`92
`93
`94
`95
`96
`97
`
`...
`
`127
`
`51
`52
`53
`54
`55
`56
`57
`58
`59
`60
`61
`62
`63
`64
`65
`66
`67
`68
`69
`70
`71
`72
`73
`74
`75
`76
`77
`78
`79
`80
`81
`82
`83
`84
`85
`86
`87
`88
`89
`90
`91
`92
`93
`94
`95
`96
`97
`98
`
`...
`
`128
`
` 1
` 3
` 5
` 7
` 9
`11
`13
`15
`16
`17
`18
`19
`20
`21
`22
`23
`24
`25
`26
`27
`28
`29
`30
`31
`32
`32
`33
`33
`34
`34
`35
`35
`36
`37
`38
`39
`40
`41
`42
`43
`44
`45
`46
`47
`48
`48
`49
`49
`50
`51
`
`123456789
`
`10
`11
`12
`13
`14
`15
`16
`17
`18
`19
`20
`21
`22
`23
`24
`25
`26
`27
`28
`29
`30
`31
`32
`33
`34
`35
`36
`37
`38
`39
`40
`41
`42
`43
`44
`45
`46
`47
`48
`49
`50
`
`Fascicle III.4 - Rec. G.711
`
`9
`
`

`
`Notes relative to Table 4/G.711
`
`Note 1 - The output signals of an A-law decoder will have even bit inversion as applied within the encoder in accordance with Note 2
`of Table 1a/G.711. Consequently the input signals to an A-μ converter will already be in this state, so that removal of even bit
`inversion should be embodied within the converter.
`
`Note 2 - If a μ-A conversion is followed by an A-μ conversion, most of the octets are restored to their original values. Only those
`octets which correspond to μ-law decoder output value numbers 0, 2, 4, 6, 8, 10, 12, 14 are changed (the numbers being increased by
`1). Moreover, in these octets, only bit 8 (least significant bit in PCM) is changed. Accordingly, the double conversion μ-A-μ is
`transparent to bits 1 to 7.
`
`Similarly, if an A-μ conversion is followed by a μ-A conversion, only the octets corresponding to A-law decoder output value
`numbers 26, 28, 30, 32, 45, 47, 63 and 80 are changed. Again, only bit 8 is changed, i.e. the double conversion A-μ-A, too, is
`transparent to bits 1 to 7.
`
`A consequence of this property is that in most of the analogue voice frequency signal range the additional quantizing distortion
`caused by μ-A-μ or A-μ-A conversion is considerably lower than that caused by either μ-A or A-μ conversion (see Recommendation
`G.113).
`
`The A-μ-A transparency for bits 1 to 7 was achieved by modifying the table slightly from the optimum conversion in that μ-80 is
`converted to A-81 instead of A-80, and A-80 is converted to μ-79 instead of μ-80. This has an insignificant effect on quantizing
`distortion.
`
`8 0 1 1 0 0 1 1 0
`
`7 1 1 1 1 1 1 1 1
`
`TABLE 6/G.711
`
`μ-law
`
`6 1 0 0 1 1 0 0 1
`
`5 1 1 1 1 1 1 1 1
`
`4 1 0 0 1 1 0 0 1
`
`3 0 0 0 0 0 0 0 0
`
`2 0 0 0 0 0 0 0 0
`
`1 0 0 0 0 1 1 1 1
`
`TABLE 5/G.711
`
`A-law
`
`8 0 1 1 0 0 1 1 0
`
`7 0 0 0 0 0 0 0 0
`
`6 1 0 0 1 1 0 0 1
`
`5 0 0 0 0 0 0 0 0
`
`4 1 0 0 1 1 0 0 1
`
`3 1 1 1 1 1 1 1 1
`
`2 0 0 0 0 0 0 0 0
`
`1 0 0 0 0 1 1 1 1
`
`10
`
`Fascicle III.4 - Rec. G.711