5i'
MONTAGE : FIN DU S 5.7 ENT  TE DE CETTE PAGE
6 Algorithms for transmission planning (from Ellemtel,
Sweden)
This Section compares loudness ratings calculated by algo
rithms as defined in the IEEE, the OREM8 and the
Recommendation P.79 standards with P.79A, an adaptation of
Recommendation P.79 for transmission planning. The computations
encompassed 71 different telephone set characteristics and 27 cases
of subscriber cable attenuation distortions.
The results show that, in typical transmission planning situa
tions, the loudness ratings by P.79A are closely related to the
others. In addition, P79A has the best additivity accuracy and the
simplest form. Administrations are therefore urged to make some
comparative studies using this P.79A algorithm in transmission
planning.
6.1 Introduction
Some preliminary comparisons between different loudness loss
estimation methods for telephone network transmission planning are
presented (sidetone algorithms are not treated, however). The
methods discussed are all based on objective measurements on tele
phone instruments.
The transmission planner has some basic requirements:
1) to obtain a meaningful and reliable indication
of the telephone speech transmission quality as regards the acous
tic loss between the talking subscriber's mouth and the listening
subscriber's ear;
2) to characterize the individual parts of a con
nection by numerical values in such a way that their sum equals the
acoustic loss measure of the complete connection;
3) to ensure that the numerical values can be
determined reliably, inexpensively and with sufficient accuracy
from measurements.
The third requirement means that for quality control and
daytoday use only objective  electroacoustic measurements can
be considered. Of course, subjective measurements have been abso
lutely necessary in the past to establish the general level of
reference. But they are more costly to carry out and give far less
repeatable results even under favourable conditions. For example
the CCITT Laboratory has periodically made subjective reference
equivalence measurements on the same stable telephone set since
late 1981. The values seem to wander slowly with time within a 3 dB
range. See [12].
6.2 Different loudness rating methods
Objective electroacoustic loss (or sensitivity) measurements
form the basis of several planning methods used by Administrations
for their national networks. The most important of these "loudness
ratings" are listed below, in the order most widely applied.
1) IEEE standard . This is now used in the USA and
Canada. It is welldocumented and reliably instrumented (see S 1
and [1]).
2) OREMB standard  (in different versions). The
version worth comparing to is currently being more accurately rede
fined by a standardization body in the Federal Republic of Germany.
3) Reference equivalents , but determined objec
tively by some kind of instrumentation. It should be noted that the
"reference loss" of a junction circuit is often determined as the
dB average over a log(f)scale.
4) Recommendation P.79. This is the "youngest"
standard. The U.K. has the widest experience in its application.
From a transmission planner's point of view it leaves something to
be desired, and a possible modification is described in [13].
Of course, to ensure telephone speech loudness quality in
international connections it is desirable that Administrations
employ methods for loudness rating evaluations which are compati
ble, or preferably identical. The aim of this exposition is to show
that for transmission planning a modified, or amended, version of
Recommendation P.79 is compatible with the IEEE, the OREMB and the
original Rec. P.79 standard, as well as with some aspects of the
reference equivalent practice. In addition, this amended
P.79 algorithm needs much less computation effort. (The principles
are given in [13] and in S 5).
For a transmission planner the most important loudness parame
ters are the send, the receive and the junction loudness ratings.
Note that the send and receive loudness ratings for transmission
planning purposes do not have to relate uniquely to subjective
values determined by comparison with some reference telephone sys
tem setup. The important aspect is that the
(send + receive + junction) loudness ratings add up to the correct
overall loudness rating (OLR), which in turn should have a good
correlation with a subjective measure. (But this cannot mean that
different countries can use different ratings that subdivide the
OLR differently!)
What order of computation accuracy is needed? With regard to
the additivity of loudness ratings as well as for setting limits in
a national transmission plan, 0.5 dB accuracy would probably be
adequate. For translating between different standards, 1.5 dB seems
sufficient. (The loudness rating manufacturing tolerances for tele
phone sets, however, have to be much wider).
6.3 Basics of the loudness rating methods
The physiological background to the loudness rating methods is
as follows:
The ear functions as a bank of narrow bandpass filters. (About
64 equivalent filters having bandwidths of 50500 Hz, called "crit
ical frequency bands"). In a specific band only, that portion of
the sound energy which lies above the hearing threshold is
presented to the brain as a stimulus. The brain combines all filter
outputs of a complex sound (such as the human voice) into an
impression of loudness.
Each filter contributes in proportion to an exponent m  of
its output power, m  being in the order of 0.20.3 for normal
speech levels. For very low levels, near the threshold of hearing,
as well as for very high levels, m equals 1, corresponding to
power addition. But it is important to note that for normal tele
phone speech, weaker spectral components contribute more to the
total loudness impression than if they were added on a direct power
basis. As a matter of fact, they approximately add on a linear
dB scale.
A more complete theory of hearing, according to Zwicker, also
takes into account certain masking effects between the stimuli from
the different frequency bands. For telephone purposes, however, the
Zwicker method does not seem to give any better agreement with sub
jective values. See [11] and [7].
In an active telephone connection the listener's impression of
loudness is influenced by his own hearing sensitivity/frequency
curve and the talker's speech spectrum. A general loudness rating
thus has to consider the statistical average for the human popula
tion.
The loudness rating algorithms mentioned can all be written in
the following form:
where
L0, m  and Ki  are constants. The index "i " refers to
the frequency fi.
Li  is the appropriate measured and/or computed elec
troacoustic loss in dB for send, receive, overall and junction rat
ing respectively.
The coefficients Ki  depend on the "average" speech and hear
ing properties, some average transmission characteristics of a typ
ical circuit, as well as the spacing between the frequencies fi.
Thus the Ki's are in general frequencydependent with proportion
ally lower values at the band edges. (An example of how to deter
mine the Ki's is found in [6]). However, the exact form of the
Kivariation is not very critical, as will be shown in the follow
ing.
A useful insight into the mathematical behaviour of the loud
ness rating formula can be had from a Taylor series expansion. Put
Equation (61b) can now be written as
ignoring higherorder terms. Here
The coefficient a  is small, in the range 0.02 to 0.03 for m
 in the range 0.175 to 0.3.
Thus, the exact value of m  is quite uncritical, as will be
shown numerically below. As a matter of fact, the second term in
equation (64) can be almost disregarded if the Li's deviate only
moderately from the average Lm, which is the case for most tele
phone send and receive characteristics.
This explains why send, receive and junction loudness ratings
can be added to get the overall loudness rating, at least as long
as no hard bandlimiting is included in the frequency range.
Moderate variations in the coefficients Ki  between diferent
algorithms can of course be interpreted as small correction terms
to be added to the Li's. Thus, the results from different algo
rithms can be expected to differ only by some constants, fairly
independent of the telephone set characteristics.
Similarly, other corrections involving small
frequencydependence can also be treated as constants added to the
loudness ratings (for example earcap leakage, difference between
measuring setups, etc.).
In practice, the transmission bandwidth of a telephone connec
tion may of course differ, depending on what type of links are
included. Discussions of how this can be handled when determining
the loudness rating can be found in [13] and in S 5, which propose
an amendment to Rec. P.79.
To investigate the properties of various loudness rating algo
rithms it is useful to make computations for a number of typical
telephone set characteristics. Below, seventyone widely different
characteristics have been used to obtain a statistical picture. See
Annex B for details.
6.4 Particulars about some algorithms
Only the mathematics of the algorithms are dealt with. Differ
ences in the measuring arrangements are not considered here. The
statistics refer to computations using the 71 different set charac
teristics as mentioned above. The result of the computations are
given with 0.01 dB precision only to show the differences clearly.
This "accuracy" is of course not at all necessary or useful in
practice.
6.4.1 IEEE standard
The computation range is 0.3 to 3.4 kHz with m = 0.22. The
Kiweighting is flat on a log ( f )scale, i.e. all Ki's are equal
except the end points which have half the value. (From a physiolog
ical point of view the weighting should really taper off slightly
at the band edges).
In the calculations presented here, 43 frequency points have
been used.
6.4.2 OREMB standard
Measurements of OREM values have traditionally been made with
special electroacoustic instruments. Recently, however, FTZ in the
Federal Republic of Germany has found it possible to compute OREMB
values according to Equation (61) using measured sensitivity
curves [14].
The computation range is 0.2 to 4 kHz with m = 0.3. The
Kiweighting is flat on a log ( f )scale as for the IEEE method,
but for the send and overall loudness ratings the loss of a SFERT
filter is added to Liin Equation (61). Fiftythree frequency
points are used.
6.4.3 Rec. P.79 standard
The computation range most often used is 0.2 to 4 kHz with
m = 0.175. The constants L0and Ki  are transformed into the
socalled Wiweights which are added to the Li's. The earcap leak
age LEis included for RLR and OLR.
The Wi's are of course tabulated in Recommendation P.79 and
the corresponding Ki's are shown in diagrams in [7]. Fourteen fre
quency points, spaced 1/3 octave apart, are used.
The Rec. P.79 constants were tailored to make computed loud
ness ratings agree with the correspondings subjective values
obtained by a specific CCITT test team some years ago. Therefore,
in some respects Rec. P.79 does not quite represent subjective
values obtained by "ordinary" people. Rec. P.79 puts too much
emphasis on the lower frequencies and the weighting coefficients
show some peculiar irregularities. (See [11] and [7] for a discus
sion.) Also, if a connection contains links of different bandwidths
some ambiguity may occur.
When applying Rec. P.79 in practice, computer programs are
most often used. Telephone set sensitivity curves and chain matrix
data of the individual links are the inputs, and SLR and RLR are
computed to an interface terminated by 600 ohms (which, inciden
tally, may not be the nominal impedance at that point!). JLR is not
calculated very often.
6.4.4 An amended Rec. P.79 standard: P.79A
Details of this proposal are given in [13].
Eleven frequency points spaced 1/3 octave apart, are used. The
computation frequencies start at 0.315 and end at 3.15 kHz, making
the range extend virtually from 0.3 to 3.4 kHz.
The Ki's are all equal to 0.1 except for the end points where
they are equal to 0.05. This trapezoidal weighting thus takes some
account of the physiological facts about speech spectrum and hear
ing sensitivity curves.
Loudness rating for tandemconnected links of wider bandwidths
than 0.33.4 kHz is taken care of by the "loudnessimprovement" E
factor, which is subtracted from OLR.
In the more "exact" version of the amendment, m = 0.2. This
is here designated "P.79A1".
A simpler approach is to let m = 0, i.e. use the weighted
loss average according to Equation (63). This version is here
designated "P.79A".
In Equation (61) the constant L0is:
for SLR:  3
for RLR: 12
for OLR: 9
for JLR: 0
When using P.79A1 or P.79A there is much less need for complex
computer programs. The LRs of the individual links can be added
with good accuracy.
6.4.5 Dependence on the mvalue
The designation "d " is used to illustrate the change of a
loudness rating as a function of the coefficient m . The "norm"
value of a particular standard corresponds to d = 0.
It can be seen from Table 61 that the choice of m  is very
uncritical. It explains why P.79A1 with m = 0.2 and P.79A with m
= 0 are fairly equivalent.
H.T. [T19.19]
TABLE 61
Values of d (i.e. changes in LR) as a function of m
(Statistics from 71 telephone set characteristics)
______________________________________________________________________________
Send Receive
Standard m Mean Standard deviation Mean Standard deviation
______________________________________________________________________________
IEEE 0.175 0.15 0.05 0.22 0.02
0.2 0.05 0.02 0.08 0.01
0.22  0.05 0.02  0.08 0.01
______________________________________________________________________________
OREMB 0.175 0.21 0.13 0.22 0.11
0.2 0.13 0.10 0.14 0.08
0.3  0.05 0.02  0.08 0.01
______________________________________________________________________________
P.79A1 0.02  0.33 0.21  0.07 0.07
0.175  0.05 0.03  0.01 0.01
0.2  0.05 0.02  0.08 0.01
______________________________________________________________________________







































































































Table 61 [T19.19], p.
6.4.6 Additivity properties
An indication of how well a certain algorithm is suited for
planning purposes is how closely the sum of send, junction and
receive ratings corresponds to the overall rating. The difference
between OLR and the sum of SLR + JLR + RLR is denoted as "D ".
Of special interest is how links of different bandwidths are
treated. In a local, analog network the transmission range can be
considered as 0.2 to 4 kHz. In a longdistance network (including
international links) one can hardly be assured of transmission out
side the range 0.33.4 kHz. Modern PCM systems, digital
exchanges, etc., may have an effective band of 0.23.4 kHz.
The IEEE standard only deals with the "narrow band"
0.33.4 kHz.
The amended P.79 standard (P.79A1 and P.79A) uses the same
"narrow band" for SLR, RLR and JLR calculations. If the actual
transmission band is wider, the sum is diminished by a "loudness
improvement factor" E to obtain an OLR which has a good correlation
with subjective loudness impressions. (See [13] and S 5.)
The unmodified P.79 standard for practical cases uses the
range 0.24 kHz. Depending on the bandwidths of the links and the
choice of interface to which the SLR and RLR calculations refer,
some ambiguity can then occur.
In Table 62 values of D are given and, for reasons of simpli
city, the junction is considered to have a flat frequency response
over the frequency band considered.
Note the large errors when P.79 is applied to a "narrow band"
connection such as can be expected in international calls.
The IEEE standard has the second worst additivity performance.
(But it is of course satisfactory in practice.)
H.T. [T20.19]
TABLE 62
Values of D = OLRSLRRLR; JLR = 0
(Statistics from 71 telephone set characteristics)
________________________________________________________________________________
Algorithm Band (kHz) D (mean) Standard deviation D (max.) D (min.)
________________________________________________________________________________
IEEE 0.33.4 0.84 0.24 1.42  0.08
OREMB 0.24.4 0.19 0.24 0.62 0.48
P.79 0.24.4 0.48 0.19 0.11 0.98
P.79 0.23.4 0.12 0.13 0.17  0.56
P.79 0.33.4 1.78 0.09 1.60 2.09
P.79A1 0.33.4 0.06 0.20 0.45 0.70
P.79A 0.33.4 0.06 0.20 0.45 {

0.70
}
________________________________________________________________________________



























































































Table 62 [T20.19], p.
6.5 Numerical comparisons between loudness ratings of dif
ferent standards
6.5.1 P.79 algorithm
From a transmission planner's point of view, the use of the
simple loudness rating algorithm P.79A seems attractive. It is then
of special interest to compare with results obtained when applying
the "normal" P.79 algorithm.
Table 63 shows the differences for SLR, RLR and OLR for con
nections having different bandwidths. (The frequency response is
assumed to be flat within the passband, however.)
H.T. [T21.19]
TABLE 63
Values of D = LR(P.79)LR(P.79A)
(Statistics from 71 telephone set characteristics)
______________________________________________________________________________
LR Band (kHz) D (mean) Standard deviation D (max.) D (min.)
______________________________________________________________________________
SLR 0.24.4 1.12 0.53 0.15 2.61
0.23.4 0.93 0.55 0.32 2.47
0.33.4  1.0 0.38 1.68 0.03
______________________________________________________________________________
RLR 0.24.4 0.65 0.46 0.43  1.95
0.23.4 0.46 0.47 0.61 1.73
0.33.4  1.52 0.31 2.06  0.55
______________________________________________________________________________
OLR 0.24.4 0.85 0.69 0.58 2.57
0.23.4 0.77 0.71 0.72 2.54
0.33.4  0.75 0.54 1.78 0.59
______________________________________________________________________________


































































































Table 63 [T21.19], p.
It can be seen from Table 63 that the P.79 and the P.79A
algorithms are reasonably equal to each other, considering the
bandwidth ambiguity of the P.79. They seem to give the same numeri
cal values (on the average) for a connection having a slightly nar
rower effective band than 0.23.4 khz but broader than 0.33.4 kHz,
i.e. a case often to be expected in practice.
As mentioned earlier, the junction loudness rating, JLR is of
less importance when using P.79 in practice. As a matter of fact
JLR (P.79) can give somewhat misleading results because of the band
edge peculiarities of the algorithm as discussed earlier.
JLR values calculated by the P.79A1 and P.79A algorithms are
more useful to the network planner for several reasons. The addi
tivity properties are better, and some previous investigations
indicate good agreement with subjective measurements of loudness
loss ([15]). (As a matter of fact the Swedish Administration has
used similar algorithms for 20 years.)
The more "complete" algorithm P.79A1 may be safely assumed to
give the closest agreement with subjective measurements of JLR. For
the transmission planner it is of interest to compare with:
a) JLR results when using the still simpler algo
rithm P.79A.
b) Circuit losses as defined by the difference in
relative levels (= L1).
When the frequency response curve is flat all these quantities
are of course identical. But typical unloaded subscriber cable
introduces a high degree of attenuation distortion in the telephone
channel. A number of cases (27) have been investigated, including
different cable diameters, d.c. resistance (lengths) and termina
tions.
For these investigations the cable data were: capacitance
45 nF/km; diameters 0.4, 0.5 and 0.7 mm; lengths corresponding to
300, 600 and 1200 ohms d.c. resistance. The terminations were 600,
900 ohms and a typical complex impedance (200 ohms in series with a
parallel combination 820 ohms and 115 nF).
The difference of JLR calculated using two algorithms is
presented in Figure 61 as a function of the cable attenuation
distortion, i.e. the difference between the loss at 4 kHz and the
loss at 0.2 kHz. (For the same length of a cable, the complex
impedance termination gives the largest distortion. In practice,
distortions larger than about 15 dB should be avoided for various
reasons.)
As can be seen from Figure 61 the P.79A algorithm is suffi
ciently accurate to be used for JLR calculations, the differences
being less than 0.3 dB for a distortion up to 15 dB.
Figure 61, p.
The subscriber cable loss as defined by L1, the difference in
relative levels, is simply the (composite) loss at 1 kHz according
to the CCITT definition (even for a complex impedance termination).
Figure 62 shows that the difference to the "true" JLR value is
always less than 1 dB, and presumably less than 0.5 dB in the
majority of practical cases.
Thus the difference in relative levels, L1, can also be used,
with good accuracy, as a measure of the change in loudness
rating, JLR. This makes the task easier for the network planner.
Figure 62, p.
6.5.2 IEEE and OREMB algorithms
To what degree will it be possible to make simple conversions
between P.79A and the IEEE and OREMB standards? That is, what is
the difference
D = LR  LR (P.79A) ?
(66)
Of interest are the average D (mean) and the standard devia
tion for typical telephone set characteristics. Because possible
differences in measuring setups have not yet been investigated, it
is for the moment only relevant to study the standard deviations.
The computation results are presented in Table 64. The stan
dard deviations are quite small, indicating that it will indeed be
feasible to make simple conversions.
H.T. [T22.19]
TABLE 64
Standard deviation of [LRLR(P.79A)]
(Statistics from 71 telephone set characteristics)
________________________________________________________
Standard LR Band (kHz) Standard deviation
________________________________________________________
IEEE Send 0.33.4 0.31
Receive 0.1
Overall 0.4
________________________________________________________
OREMB Send 0.24.4 0.52
Receive 0.38
Overall 0.5
________________________________________________________


















































Table 64 [T22.19], p.
6.6 Conclusions
A proposed amendment, P.79A, to the loudness rating
Recommendation P.79 has been investigated and found adequate for
transmission planning purposes. (The algorithm P.79A corresponds in
principle to taking a weighted dB average over a log ( f )scale.
See S 6.4.4 and [13].
The algorithm P.79A has been shown to give, with sufficient
accuracy, numerically equal values with P.79 in typical transmis
sion planning situations. P.79A can be expected, for good reasons,
to agree better with subjective values than P.79.
It also seems possible to make simple conversions between
P.79A, IEEE and OREMB loudness ratings.
P.79A has the best additivity accuracy as well as the most
simple form.
Administrations are therefore urged to make some comparative
studies using this P.79A algorithm in transmission planning.
7 Information on the Zwicker loudness rating method as used
by the French Administration (Contribution from the French Adminis
tration)
7.1 Introduction
The method recommended for the evaluation of the quality of a
communication in terms of loudness is that of loudness rating (LR).
The subjective determination of these equivalents is described in
Recommendation P.78, and the objective determination in
Recommendation P.79.
However, other parameters (e.g. R25E) have been used, and no
universal formula is available to transform these parameters
into LR. Therefore it will be useful to have a description of how
both values (e.g. R25E and LR) can be objectively measured for a
given equipment.
This Section sets out to describe a method for an objective
evaluation of loudness losses (R25 equivalents and loudness rat
ings) used by the French Administration, as stated in the
SG XII/3 Report, in Boglarlelle, May 1987 (TD64 revised).
7.2 Characteristics of the method
The computation of the loudness of stationarytype signals
using the Zwicker algorithm, when applied to the objective measure
ment of R25 equivalents and LR, gives results which are in good
agreement with results obtained using the corresponding subjective
evaluation methods [16].
One specific characteristic of this algorithm is that it can
be used to compare loudness between systems whose transmitted fre
quency bandwidth is not within the limits of 3003400 Hz.
Adaptations of the Zwicker algorithm to monaural and binaural
listening modes respectively are used to evaluate different types
of terminals: handset telephones [16], operator headsets [17] and
loudspeaker telephones [18].
It is essential to use "complex" voices as defined in
Recommendation P.51 to measure nonlinear systems. This algorithm
has lead to satisfactory results in the evaluation of handfree
sets [19] when using such input voices.
7.3 Principle of Zwicker's algorithm to calculate loudness
The method is based on the use of method B of ISO 532 Rec.
(Zwicker method).
7.3.1 Essential phenomena considered in the calculation of
loudness
The algorithm establishes a relationship between the stimulus
(physical) and the auditory sensation (psychoacoustical). Loudness
is composed of three main phenomena which are as follows: critical
bands, masking and equal loudness levels.
7.3.1.1 Critical bands
In the human ear, wideband sounds seem to be louder than pure
or narrowband sounds with the same acoustic pressure levels. It is
also possible to prove that, around a given frequency and for a
fixed level of acoustic pressure, loudness remains constant as long
as the sound bandwidth does not exceed a given value called the
critical band. If sound bandwidth exceeds this value, a distinct
increase in loudness can be noted. In this way, the ear divides the
domain of audible frequencies into 24 critical bands, within which
any excitation is integrated without weighting. Therefore, loudness
measurement is based upon spectral sound analysis.
7.3.1.2 Masking effect
The masking effect consists of raising a (reference) sound's
threshold level of audibility when transmitting another sound of a
(masking) noise with a lower frequency (or higher, but in a weaker
proportion). This can be explained via the notion of specific loud
ness.
7.3.1.2.1 Specific loudness
A narrow band of noise or a pure sound, whose spectral energy
is concentrated at one specific point of the frequency range,
causes a large portion of the basilar membrane (one of the essen
tial auditory organs) to vibrate. This causes not only an excita
tion of the centre, but also an excitation of the sides which is
especially significant in frequency zones above that of the signal
frequency. The effect of these side excitations shows itself via
the masking effect. The excitations of the centre and the sides
contributes to the specific signal loudness.
7.3.1.2.2 Masked or partially masked loudness
If a weak sound falls in the highest frequency zone as defined
above, it can be masked partially or totally by the side excita
tions, and therefore does not produce any specific loudness.
7.3.1.3 Equal loudness levels
The ear is not equally sensitive to different frequencies;
curves of equal loudness levels allow to compare the loudness of
sounds produced by sounds of different frequencies once the signal
levels have been physically measured. On an "acoustic pressure
level vs. frequency" diagram, these curves link the points which
correspond to an equal sensation of sound loudness, including those
found at the threshold of hearing.
7.3.2 Global loudness of a complex sound
Using a spectral analysis in thirds of octaves the Zwicker
method [20] is used to calculate the loudness of stationary signals
with the following double correction:
 by transforming the pressure level in each third
octave band into a specific loudness,
 by a specific loudness summation, weighted by the
masking effect.
7.3.3 Computer measurement of loudness
This measurement is possible since the acoustic pressure level
for each third octave band is known. The FORTRAN program enabling
this loudness to be computed is described in [21].
Note  The Zwicker algorithm includes two variants: one for
listening in a free field, the second for listening in a diffuse
field. Results referenced in [16], [17] made use of the first
variant. Both lead to satisfactory values when applied for the
determination of R25 and LR.
7.4 Application of the Zwicker method for measuring the
loudness loss (LL): R25 equivalents (R25E) and loudness ratings
(LR)
7.4.1 Fundamental principle of the objective LL measuring
method
The principles on which the following instrumental method are
based are similar to the subjective methods described in
_________________________
Third octave bands are a good approximation of the
critical bands, provided that bands lower than 280 Hz
are appropriately grouped together.
Figures 71 and 72 for determining the R25 equivalents and LR. In
this method:
a) The speech signals are replaced by an artificial
acoustic voice, the spectral characteristics of which are given in
Recommendation P.51.
b) The reference parameters and signals are calcu
lated on the basis of the nominal efficiency characteristics, as a
function of the frequency of the NOSFER and IRS defined in P.42
(Red Book) and P.48. These are:
 the artificial electric voices resulting from the
transmission of acoustic artificial voice via reference transmis
sion systems,
 the NOSFER reference loudness (RL),
 the loss x2as a result of comparing and equaliz
ing the loudness of NOSFER and IRS paths.
c) The values of "LE " relative to acoustic leak
age are used as artificial ear/real ear correcting terms.
d) Operator evaluation of sound loudness is
replaced by a calculation of the loudness of stationary noise
intercepted by a standardized artificial ear, and is performed
according to Zwicker's algorithm.
Figure 71, p.
Figure 72, p.
7.4.2 Characteristics of reference signals and parameters
The reference signals and parameters which objectively charac
terize speech communication in Figures 71 and 72 are defined
hereafter.
Note  Whether it is a question of human or artificial mouths
and ears, the definition of mouth and ear reference points (MRP and
ERP) does not change (Annex A of Recommendation P.64) and the
standardized speaking positions are identical.
 Acoustic artificial voice: defined at the MRP.
For spectral characteristics, see Table 2/P.51.
 Electrical artificial voices: these voices sub
stitute, at points JS in Figures 71 and 72, for the human
voice/NOSFER or IRS systems. For spectral characteristics see
Tables 71 and 72 (columns NT and NSrespectively).
 Reference loudness (RL): loudness of the acous
tic signal at the e.r.p. of "path 0", when the acoustic artificial
voice is applied to the MRP.
RL = 21.1 sones
 x2: loss calculated according to the flowchart
in Figure 74 to give equal loudness for paths 0 and 2 (Fig
ure 72).
x2= 21.5 dB
 Acoustic leakage "LE": defined in two cases:
i) for the telephone set receiver (Table 4/P.79)
ii) for the NOSFER receiver (Table 73, LER).
H.T. [T23.19]
TABLE 71
Electrical artificial voice of the NOSFER
(output of the NOSFER sending system)
_________________________________________________________
Frequency (Hz) N (dBV) Frequency (Hz) N (dBV)
_________________________________________________________
100 29.7 1000 20.3
125 24.7 1250 22.1
160 21.4 1600 24.3
200 19.2 2000 26.0
250 18.6 2500 27.8
315 18.4 3150 28.1
400 18.7 4000 29.9
500 18.7 5000 34.8
630 18.8 6300 42.7
800 19.4 8000 46.4
_________________________________________________________

































































Table 71 [T23.19], p.
H.T. [T24.19]
TABLE 72
Electrical artificial voice of the IRS
(output of the IRS sending system)
_________________________________________________________
Frequency (Hz) N (dBV) Frequency (Hz) N (dBV)
_________________________________________________________
100 68.9 1000 22.6
125 55.3 1250 23.3
160 42.0 1600 23.6
200 33.6 2000 24.8
250 27.7 2500 25.1
315 23.8 3150 26.8
400 21.7 4000 67.0
500 21.0 5000 82.8
630 21.5 6300 104.5
800 21.9 8000 120.5
_________________________________________________________

































































Table 72 [T24.19], p.
H.T. [T25.19]
TABLE 73
NOSFER receiver acoustical leakage
_________________________________________________________
Frequency (Hz) LE (dB) Frequency (Hz) LE (dB)
_________________________________________________________
100  0.9 1000 4.5
125  0.2 1250 3.9
160 0.6 1600 4.6
200 1.6 2000 3.3
250 2.9 2500 3.2
315 4.2 3150 3.3
400 5.3 4000 3.7
500 5.4 5000 2.9
630 4.9 6300 0.8
800 4.6 8000 0.8
_________________________________________________________

































































Table 73 [T25.19], p.
7.4.3 Loudness loss computation
Generally, the measurement consists in comparing and setting
the reference loudness (RL) equal to the loudness of the various
paths being studied (Figures 71 and 72). However, considering the
structural modification of these paths (see S 7.4.2), the analogy
between the subjective and the objective method is only possible if
the signals which characterize these paths have been corrected
(iterms of Figures 73 and 74: acoustical leakage, nominal
sensitivity/frequency of the reference receiving systems) before
calculating their loudness and comparing them to the reference.
The R25 equivalents and LR are therefore calculated according
to the flowcharts in Figures 73 and 74.
Figure 73, p.
Figure 74, p.
7.5 General structure of the CERF apparatus of the French
Administration
The diagram in Figure 75 shows how the main elements of the
measuring device performing the operation described above are
organized. [22] gives a detailed description of the functions and
features of the device.
Figure 75, p.
8 Information on the OREMB loudness loss method as used by the
Administration of the Federal Republic of Germany (Contribution by
the Administration of the Federal Republic of Germany)
8.1 Definition
Within the area of the Deutsche Bundespost, measurements of
loudness ratings are performed according to DIN 44013 "Objective
Reference Equivalent Measuring Device OREMB, Configuration and
Application."
8.1.1 OREMB loudness related ratings, BD
By definition, the loudness BD is zero if a sound pressure of
1.6 Pa is reached at the SFERT microphone in the Braun ear at a
sound pressure of 1.07 Pa under the measurement conditions speci
fied in DIN 44013.
8.1.2 OREMB send loudness, SBD
The send loudness determined by operating the test item
(e.g. a telephone set together with the feeding bridge, possibly
also with connected lines and other equipment) as an electric
transmitter and by comparing the voltage measured at a 600 ohm ter
minating impedance with the reference voltage.
By definition, the "SBD" is zero if the output voltage at the
SFERT microphone in the presence of a 1.07 Pa sound pressure is
285 mV (see Figure 81).
Figure 81, p.
8.1.3 OREMB receive loudness, EBD
The receive loudness determined by operating the test item
(e.g. a telephone set together with the feeding bridge, possibly
also with connected lines and other equipment) as an electric
receiver and by comparing the sound pressure measured in the Braun
ear with the reference sound pressure.
By definition, the "EBD" is zero if the sound pressure meas
ured at an opencircuit voltage of the transmitter of 570 mV
(internal resistance: 600 ohms) is 1.6 Pa (see Figure 81).
8.1.4 OREMB overall loudness, OBD
(Overall loudness (OBD) of a telephone connection): The refer
ence equivalent determined by comparing a complete telephone con
nection, possibily together with interposed lines and other equip
ment, with the OREMB reference transmitter and receiver (see Fig
ure 81).
8.1.5 OREMB sidetone loudness, RBD
The sidetone loudness determined by comparing  in transmis
sions from the microphone to the receiver capsule of the same test
item (e.g. a telephone set with a specific terminating impedance)
the sound pressure of the receiver with the reference sound pres
sure.
By definition, it is zero if the sound pressure measured in
the Braun ear is 1.6 Pa in the presence of a sound pressure of
1.07 Pa at the SFERT microphone.
8.2 Measurement conditions deviating from Rec. P.64
 Instead of the handset position according to
Annex A of Rec. P.76 [the loudness rating guardring position
(LRGP)], a position according to Rec. P.72 [reference equivalent
speaking position (RESP) (Red Book) ] is used.
 Instead of the IEC coupler, a Braun coupler is
used.
 Use is made of an artificial mouth according to
Rec. P.51.
 Calibration of the artificial mouth is not per
formed under freefield conditions but with the aid of the SFERT
baffle. The sound pressure buildup in the SFERT baffle is compen
sated by an adequate filter in the generator section. At the
diaphragm of the microphone in the SFERT baffle (see Figure 82),
spaced 43.5 mm apart from the lip plane, the sound pressure is set
to 1.07 Pa (sound pressure level: 94.6 dB). Between 200 Hz and
4000 Hz, the sound pressure should be as frequencyindependent as
possible. In the process, the SFERT filter is activated.
 Via a regulation loop, the sound pressure is
kept constant at the calibration value (independently of the test
item).
Figure 82, p.
8.3 Algorithm
The successive voltages U1, U2.   Un  of the swept
sinusoidal signal are added according to the following law:
for ti  approching 0:
The exponent m  is 0.6.
The static transient time of the indicator is 3.5 s.
The frequency sweep 200 .   4000 .   200 Hz is logarithmic
with time, with a complete sweep cycle per second.
ANNEX A
(to Supplement 19  ref. to S 5.3)
Efactor coefficients
The attenuation values Li  are given for the "wideband" f1 .
  fN. The "wideband" LR (W ) is computed using the algorithm:
For shortness we use the notation:
The "common" band LR is computed in the narrower range:
According to the definition of the Kicoefficients we have:
The relationship between the two algorithms is defined to be
as follows:
For a strictly bandlimited system, i.e. one for which L1 . 
 LN\d1 = oo, we let:
and further we set:
Thus, we get:
and
We will use the following notation:
In the general case we have:
which results in
As the terms in the sum ~" ` in Equation (A11) are small, one
can make a series expansion. Thus:
where
The last term in Equation (A12) is designated as the loudness
improvement, the E factor.
In the actual case the "wideband" can be taken to encompass
the range f1 = 200 Hz to f1\d4 = 4000 Hz and the "common" band
f3 = 315 Hz to f1\d3 = 3150 Hz. The "band edge" frequencies are
200, 250 and 4000 Hz.
The coefficients Ci  have been computed for some LR algo
rithms under discussion using the Kivalues for OLR as given in
Table A1. (Details of the algorithms are given in [11] and [7] as
well as the method used for converting Wiweights to Kiweights.)
The Civalues are presented in Table A2.
The P.79 algorithm or its smoothed version P.79/S are not
suitable for band edge performance, analysis as their frequency
weighting has been shown to be less correct (too much emphasis on
the lower frequencies [7].)
It is apparent from Table A2 that the Cicoefficients from
the three algorithms do not differ very much. As the human speech
and hearing characteristics at the band edges can be expected to
vary rather much, the actual values of the Ci's cannot be critical.
Therefore, it is reasonable to use the "roundedoff" values:
and to set m = 0.2.
Which algorithm should be used when computing the
"common"band LR? As shown in [11] and [7], there are several algo
rithms which correlate about equally well with subjective measure
ments. The simplest one is the algorithm "C " which was therefore
chosen.
H.T. [T26.19]
TABLE A1
___________________________________________________
K
Algorithm m 0.2 kHz 0.25 kHz 4 kHz
___________________________________________________
P.XXE 0.225 0.0227 0.0389 0.0292
CH 0.2 0.0306 0.0439 0.0324
B 0.2 0.031 0.042 0.042
P.79/S 0.175 0.0536 0.0765 0.0243
___________________________________________________














































Table A1 [T26.19], p.
H.T. [T27.19]
TABLE A2
__________________________________________________
C
Algorithm
0.2 kHz 0.25 kHz 4 kHz
{
__________________________________________________
P.XXE 0.48 0.83 0.62 1.93
CH 0.74 1.06 0.79 2.59
B 0.76 1.03 1.03 2.82
Mean 0.66 0.97 0.81 2.45
__________________________________________________
































































Table A2 [T27.19], p.
Blanc
ANNEX B
(to Supplement 19  ref. to S 6.3)
Seventyone telephone set characteristics were obtained of
which:
a) thirteen from CCITT COM XIINo. 164 (19771980),
and
b) fiftyeight from Barnes in a private communica
tion.
The statistics of the send and receive sensitivity curves are
shown in Figures B1 and B2. The curves were normalized by sub
tracting the "average" sensitivity computed by Equation (61b).
Figure B1, p.
Figure B1, p.
References
[1] IEEE Standard 6611979, Standard method for determining
objective loudness ratings of telephone connections , IEEE , New
York.
[2] CCITT Draft Recommendation P.XXE, Question 15/XII,
Annex 2 (II) Contribution COM XIINo. 1, Study Period 19771980,
Geneva, 1976
[3] CCITT Contribution COM XIINo. 160, Use of Zwicker's
method for computing loudness ratings (Australia), Study
Period 19811984, Geneva, 1983.
[4] BARNES (J.): Private Communication, STL.
[5] CCITT Contribution COM XIINo. 10 (People's Republic of
China), Study Period 19811984.
[6] CCITT Contribution COM XIINo. 55 (ELLEMTEL), Study
Period 19811984.
[7] CCITT Contribution COM XIINo. 194 (ELLEMTEL), Study
Period 19811984.
[8] CCITT Contribution COM XIINo. 98, Calculation of
loudness ratings for different bandwidths (British Telecom), Study
Period 19811984, Geneva, 1982.
[9] CCITT Contribution COM XIINo. 78, Additivity of loud
ness ratings (ELLEMTEL), Study Period 19811984, Geneva, 1982.
[10] CCITT Contribution COM XIINo. 111, Choice of
representative loss/frequency characteristics for electrical ele
ments (ITT/STL), Study Period 19811984, Geneva, 1983.
[11] CCITT Contribution COM XIINo. 176, Loudness rating
algorithms applied to some published data (ELLEMTEL), Study
Period 19811984, Geneva, 1984.
[12] CCITT Contribution COM XIINo. 4, The stability of the
CCITT test team . Some comments. (ELLEMTEL), Study
Period 19851988, Geneva, 1985.
[13] CCITT Contribution COM XIINo. 1, Question 15/XII
(Annex 2), Adapting loudness ratings for transmission planning ,
Study Period 19851988.
[14] Private Communication from FTZ (Federal Republic of
Germany).
[15] CCITT Contribution COM XIINo. 15, Objective measure
ment and calculation of the reference attenuation of local cables
(Sweden), Study Period 19641968.
[16] CCITT Contribution COM XIINo. 111, Subjective and
objective comparison of results concerning loudness ratings (LR)
and R25 equivalents (R25E) , Study Period 19851988.
[17] CCITT Contribution COM XIINo. 58, Determination of
loudness ratings and R25 equivalents for operator headsets, taking
acoustical leakage into account , Study Period 19851988.
[18] CCITT Contribution COM XIID.44  WPXII/2 Shangai,
1216 October 1987 Status Report of Question 17: "Loudspeaking
telephones" (see COM XIIR 20, Study Period 19851988).
[19] CCITT Contribution COM XII235, Sending objective
measurements of handsfree sets. Influence of artificial voices
characteristics , Study Period 19851988.
[20] ZWICKER, FELDTKELLER: Das Ohr als
Nachrichtenempfanger, S. Hirzel Verlag , Stuttgart.
[21] PAULUS (E.) and ZWICKER (E.): Computer programmes for
calculating loudness from thirdoctave band levels or from critical
band levels, Acustica , 1972, Vol. 27, pp. 253266.
[22] CCITT Handbook on telephonometry (CERF: an equipment
for the objective measurement of various sorts of loudness used by
the French Postal and Telecommunication Administration), ITU,
Geneva, 1987.
Blanc