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Telecommunications Industry Association
TR41.3.5-13-04-014-L
Document Cover Sheet
Project Number
ANSI/TIA-PN-470.112
Document Title
Nominal Values for SLR and RLR Tested Using 600 Ohms and No Loop
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Whitesell Consulting LLC
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Stephen R Whitesell
2 Shannon Ct
Howell, NJ 07731-8919
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TR-41.3.5
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Phone: 732 751 1079
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The document to which this cover statement is attached is submitted to a Formulating Group or
sub-element thereof of the Telecommunications Industry Association (TIA) in accordance with the
provisions of Sections 6.4.1–6.4.6 inclusive of the TIA Engineering Manual dated October 2009, all
of which provisions are hereby incorporated by reference.
Abstract
Contribution TR41.3.5-13-04-009 by AST provides measurement data on the signal delivered to/from a
600 ohm resistor representing a telephone using the 600 ohm source/load test configuration without loop
specified in the draft ANSI/TIA-PN-470.112 standard and compares it to measurements using the 900
ohm source/load configuration with a 2.7 km, 26 AWG loop that is traditional for analog telephone
testing. While the data showing cable loss as a function of frequency is as expected, the relative levels for
the send test condition at low frequencies were not as anticipated. Perhaps this is due to a
misunderstanding of the exact calibration and testing scenarios. The relative results for the receive test
conditions were about as anticipated.
This contribution calculates the expected low frequency level differences between the test conditions
based on simplifying the artificial loop circuits shown in ANSI-TIA-470.110-C. These level differences
may then be used to shift the frequency dependent results from Contribution TR41.3.5-13-04-009 for the
2.7 km loop condition and apply them to calculations of SLR and RLR for examples of send and receive
frequency responses for wideband and narrowband telephones. Companion Contribution TR41.3.5-1304-014b-L contains spreadsheets providing details of these additional calculations.
The results of the calculations do not show a significant bandwidth effect (appropriate narrowband or
wideband LR calculations were used for each case). However, they suggest nominal SLR values for the
600 ohm, no loop test condition should be about 4.5 dB less positive (louder) than for the traditional 900
ohm, 2.7 km loop test condition (SLR = 3.5 instead of 8.0). The results for receive indicate the nominal
RLR values for the 600 ohm, no loop test condition should be about 4.5 dB more negative (again louder)
than for the traditional 900 ohm, 2.7 km loop test condition (RLR = -7.5 instead of -3.0).
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Contribution TR41.3.5-13-04-009 Results
Contribution TR41.3.5-13-04-009 by AST provides measurement data on the signal delivered to/from a
600 ohm resistor representing a telephone using the 600 ohm source/load test configuration without loop
specified in the draft ANSI/TIA-PN-470.112 standard and compares it to measurements using the 900
ohm source/load configuration with a 2.7 km, 26 AWG loop that is traditional for analog telephone
testing.
For send, the telephone is represented as a 600 ohm resistive source that delivers its output either to a 600
ohm load without intervening loop (draft ANSI/TIA-PN-470.112 case) or through 2.7 km of 26 AWG
cable to a 900 ohm termination (traditional measurement as in ANSI/TIA-470.110-C). The results for the
send case are shown in Section 1.3 of the contribution. The 600 ohm termination without loop case
shows a result that is independent of frequency, while the 900 ohm termination with intervening 2.7 km
loop case shows a high frequency roll off. Both are as expected. However, the 900 ohm termination with
intervening loop case is shown to be 2.30 dB higher in level at low frequencies than the 600 ohm
termination without loop case. As discussed below, this was unexpected.
For receive, the telephone is represented as a 600 ohm resistive load that is fed from a 600 ohm source
without intervening loop (draft ANSI/TIA-PN-470.112 case) or from a 900 ohm source through 2.7 km of
26 AWG cable (traditional measurement as in ANSI/TIA-470.110-C). The results for the receive case are
shown in Section 1.4 of the contribution. The 600 ohm source without loop case shows a result that is
independent of frequency, while the 900 ohm source with intervening 2.7 km loop case shows a high
frequency roll off. Again, both are as expected. The 900 ohm termination with intervening loop case is
shown to be 5.88 dB lower in level at low frequencies than the 600 ohm termination without loop case.
This is approximately as expected.
Calculation of Low Frequency Level Differences
Clause 4.3.6 of ANSI/TIA-470.110-C contains a circuit schematic and parameter values for 26 AWG
cable sections. Parameter values are given for 0.305 km (1 kft), 0.914 km (3 kft), and 1.83 km (6kft)
cable sections that may be cascaded together to create an artificial cable of the desired length. The socalled 2.7 km loop is normally modeled using a 0.914 km (3 kft) section and a 1.83 km (6 kft) section.
The circuit schematic and parameter values are reproduced in Figure 1 and Table 1 below:
R1
R2
L1
C2
C4
C1
R3
C3
L2
R4
Figure 1 – Artificial Line Segment (Figure 5 in ANSI/TIA-470.110-C)
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Table 1 – Artificial Line Segment Component Values (Table 1 from ANSI/TIA-470.110-C)
Component
0.305 km (1 kft)
0.914 km (3 kft)
1.83 km (6 kft)
R1, R4
41.7 
124 
249 
R2, R3
109 
174 
312 
C1, C4
3.77 nF
11.3 nF
22.6 nF
C2, C3
4.02 nF
12.2 nF
25.5 nF
L1, L2
96.0 H
336 H
983 H
NOTES:
1. All values are  1 %.
2. 2.7 km (9 kft) and 4.6 km (15 kft) can be made up of cascaded
sections of the above.
3. Resistance values include resistance of series inductor
At low frequencies (~100 Hz), the inductors in the circuit may be treated as short circuits and the
capacitors as open circuits. This reduces the schematics to simple resistive loss circuits with one 124 ohm
resistor in each of the tip and ring conductors for the 0.914 km (3 kft) case and one 249 ohm resistor in
each of the tip and ring conductors for the 1.83 Km (6 kft) case.
Send Offset Calculation:
These simplified schematics are used to calculate the ratio of the voltage V delivered to the 600 ohm or
900 ohm termination to the open circuit voltage Voc provided by the 600 ohm source representing the
telephone for the send case in Figure 2.
600
Voc
600
V
600
124
249
Voc
V
124
249
3 kft
6 kft
900
𝑉
600
=
𝑉𝑜𝑐
600 + 600
𝑉
900
=
𝑉𝑜𝑐
600 + 2(124) + 2(249) + 900
𝑉
= 0.5
𝑉𝑜𝑐
𝑉
= 0.4007
𝑉𝑜𝑐
𝑉
20 log (
) = −6.02
𝑉𝑜𝑐
𝑉
20 log (
) = −7.94
𝑉𝑜𝑐
Figure 2 – Send Calculations for Low Frequency Level Differences
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For send, Voc is a function of the design and transduction efficiency of the telephone and of the input
sound pressure as measured at MRP. It will be the same independent of whether the telephone is tested
using the 600 ohm termination without loop or the 900 ohm termination with 2.7 km loop. Thus, the
level delivered to the 900 ohm termination at low frequencies (100 Hz) will be 1.92 dB lower (7.94 –
6.02) than the level delivered to the 600 ohm termination for Send measurements.
The calculated 1.92 dB lower value is notably different from the 2.30 dB higher level shown in
Contribution TR41.3.5-04-009. Normalizing the loop loss values given in that contribution to their 100
Hz values and then applying the 1.92 dB offset for the 900 ohm with loop case yields the loop loss effect
results shown in Figure 3. For the 600 ohm case without loop, the signal delivered to the 600 ohm load is
6.02 dB below the open circuit value independent of frequency. For the 900 ohm with loop case, the
signal delivered to the 900 ohm termination is 7.94 dB below the open circuit value at 100 Hz. The loss
increases only slightly with frequency up to about 1000 Hz, but then rolls of by an additional 6 dB at
4000Hz and about an additional 13 dB at 8000 Hz.
Figure 3 – Send Loop Loss vs. Frequency
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Receive Offset Calculation:
These simplified schematics may also be used to calculate the ratio of the voltage V delivered to the 600
ohm load representing the telephone to the open circuit voltage Voc provided by the 600 ohm or 900 ohm
source for the Receive case as shown in Figure 4.
600
Voc
900
V
600
124
249
Voc
V
124
249
3 kft
6 kft
600
𝑉
600
=
𝑉𝑜𝑐
600 + 600
𝑉
600
=
𝑉𝑜𝑐
900 + 2(124) + 2(249) + 600
𝑉
= 0.5
𝑉𝑜𝑐
𝑉
= 0.2671
𝑉𝑜𝑐
𝑉
20 log (
) = −6.02
𝑉𝑜𝑐
𝑉
20 log (
) = −11.47
𝑉𝑜𝑐
Figure 4 – Receive Calculations for Low Frequency Level Differences
For receive, a matched impedance calibration condition is used to establish Voc. That is, the circuit
shown on the left in Figure 3 is used to first establish Voc for the 600 ohm source using a 600 ohm
resistor for the load. The resistor is then removed and the telephone (also represented by a 600 ohm
resistor in this case) is connected to the source. A circuit like the one on the left but having 900 ohm
resistors is also used to establish Voc for the 900 ohm case. The 900 ohm load resistor is then removed
and the 2.7 km cable terminated with a 600 ohm telephone is connected for the measurement as shown in
the circuit on the right in Figure 3.
So Voc will be 6.02 dB higher than the specified matched load calibration value Vc for both the 600 ohm
source without loop and the 900 ohm source with 2.7 km loop condition. This means the level across the
600 set (and hence the acoustic output of the receiver) is 5.45 dB lower (11.47 – 6.02) for the 900 ohm
source plus loop than for the 600 ohm source and no loop if the same value of Voc is used for both cases.
In general, the specified calibration value Vc, and hence the value of Voc, will be different, but the
acoustic output of the receiver will track this difference and the RLR calculation, which is a measure of
input minus output (i.e., loss), will remain the same, assuming the system is linear. If it is not linear, then
the possible need to use receive level instead of RLR as the receive output measurement is a separate
discussion.
The calculated 5.45 dB lower value is somewhat similar to the 5.88 dB lower level shown in Contribution
TR41.3.5-04-009. Normalizing the loop loss values given in that contribution to their 100 Hz values and
then applying the 5.45 dB offset for the 900 ohm with loop case yields the loop loss effect results shown
in Figure 5. For the 600 ohm case without loop, the signal delivered to the 600 ohm load representing the
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telephone is 6.02 dB below the open circuit value independent of frequency. For the 900 ohm with loop
case, the signal delivered to the 600 ohm load representing the telephone is 11.47 dB dB below the open
circuit value at 100 Hz. As with the send case, the loss increases only slightly with frequency up to about
1000 Hz, but then rolls of by an additional 6 dB at 4000Hz and about an additional 12 dB at 8000 Hz.
Figure 5 – Receive Loop Loss vs. Frequency
Determination of SLR and RLR Differences for Frequency Response Examples
Combining the information calculated above about the difference in low frequency send levels delivered
to the 600 ohm or 900 ohm termination with the information in Contribution TR41.3.5-04-009 on the
loop loss effect as a function of frequency for the 2.7 km, 26 AWG loop allows us to take an arbitrary but
representative send frequency response curve, apply the relative loop loss effects for both test conditions,
and then shift the overall level of the curves until the calculated SLR value for the 900 ohm termination
with 2.7 km loop case meets the desired nominal value of 8 dB. The corresponding calculation of the
SLR value for the 600 ohm without loop test condition then indicates how much of a difference we
should expect due to the test conditions.
A similar approach can be taken for a representative receive frequency response curve to obtain the
nominal value of RLR = -3 dB for the 900 ohm source with loop condition and then calculate the
corresponding RLR value for the 600 ohm source without loop condition.
Companion Contribution TR41.3.5-13-04-014b-L provides the detailed calculations for determining what
the SLR and RLR values should be for the 600 ohm source/load without loop test condition to correspond
to the nominal SLR and RLR values for the 900 ohm source/load test conditions with a 2.7 km, 26 AWG
loop.
The Loop Loss Tab shows the relative loss vs. frequency data from TR-41.3.5-13-04-009 for the send
test arrangement in Column B. This data is normalized to its 100 Hz value in Column C. The calculated
1.92 dB low frequency difference is then added in Column D. Column E shows the 20 log (V/Voc) data
for the 600 ohm without loop test condition (i.e., -6.02 dB) and Column F shows the corresponding 20 log
(V/Voc) data for the 900 ohm with 2.7 km loop test condition. It is obtained by adding Columns D and E.
Columns G – K show the corresponding data for the receive test arrangement. The resulting loss vs.
frequency curves for both the send and receive directions are shown graphically on the Charts tab and
reproduced in Figures 3 and 5 of this contribution.
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The Wideband Send Tab takes an example send frequency response curve from an old TR-41.3.3
contribution,1 applies an overall level shift to it so that the calculated SLR value for the 900 ohm with
loop test condition has the nominal 8 dB value, and also calculates the corresponding SLR value for the
600 ohm without loop test condition. Column B contains the approximate 1/3 octave send sensitivity
values from the TR41.3.3-10-05-009 contribution. Column C shows the data from Column B shifted by
the amount specified in Cell C24 and forms the new reference curve for further calculations. The
determination of the shift value used in cell C24 will be explained below.
Columns D – F contain the same send loop loss data as was shown on the Loop Loss Tab. Column D
shows the relative loss vs. frequency data from TR-41.3.5-13-04-009. This data is normalized to its 100
Hz value in Column E. The calculated 1.92 dB low frequency difference is then added in Column F.
Column G is identical to Column C and provides the frequency response data for the 600 ohm without
loop test condition when the value of cell C24 is properly chosen. Column H shows the frequency
response data for the 900 ohm with loop test condition when the value of cell C24 is properly chosen. It
is obtained by adding the relative loop loss vs. frequency data in Column F to the data in Column G.
Graphs of the frequency responses in Columns G and H are included on the Charts tab.
Column I provides the Ws send weighting function from Table A.2 of ITU-T Recommendation P.79.
Columns J and K are used for performing the Send Loudness Rating calculations for the 600 ohm and 900
ohm cases, respectively, with the SLR values shown in cells J24 and K24. The 1.76 dB 900-to-600 ohm
impedance correction factor is included in the 900 ohm calculations in Column K.
The shift value in cell C24 is manipulated until the SLR value for the 900 ohm with loop test condition in
cell K24 equals the desired nominal value of 8.0 dB. Changing this value has the effect of shifting the
send frequency response in Column C up or down by the designated amount. Since the 600 ohm without
loop frequency response in Column G and the 900 ohm with loop frequency response in Column H are
tied to the values in column C, they also shift up or down by the same amount. Once the desired 8.0 dB
SLR value is achieved in cell K24 for the 900 ohm with loop test condition, the corresponding SLR value
for the 600 ohm without loop test condition may be read in cell J24. In this particular example, the SLR
value for the 600 ohm without loop case is 3.5 dB.
A similar process is used to determine RLR values on the Wideband Receive Tab and SLR and RLR
values on the Narrowband Send Tab and Narrowband Receive Tab. The wideband receive frequency
response was taken from the same TR-41.3.3-10-05-009 contribution as the wideband send response. The
narrow band send and received responses were taken from the theoretical curves used for the tutorial
information on the transition from IEEE 661 Objective Loudness Ratings (OLRs) to ITU-T P.79
Loudness Ratings (LRs) in Annex G of ANSI/TIA-470.110-C. See Table G.1 and Figures G.1 and G.2 of
that document. The receive curve is for a measurement on a sealed Type 3.1 artificial ear. Thus, the
Narrowband Receive Tab includes the insertion of new Columns C and D adding the Le ear leakage
correction to produce a “haystack shaped” response curve. The narrowband values for the Ws and Wr
weights from Table 1 of ITU-T P.79 were used for the narrowband loudness rating calculation and the
frequency band was limited 200 to 4000 Hz (band numbers 4-17).
The results of the calculations for the four examples in companion Contribution TR41.3.5-13-04-014b-L
are summarized in Table 2.
1 TR41.3.3-10-05-009. The first send frequency response shown in section 10 of that document and the first receive frequency
response shown in section 11 were used for this contribution. The approximate values of the curves at the nominal 1/3 octave
frequency values were used to provide example frequency responses.
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Table 2 – SLR and RLR Calculation Results
600 Ohm
900 Ohm
Wideband Send
SLR = 3.5
SLR = 8.0
Narrowband Send
SLR = 3.6
SLR = 8.0
Wideband Receive
RLR = -7.7
RLR = -3.0
Narrowband Receive
RLR = -7.5
RLR = -3.0
Conclusion
Compared to the 600 ohm source/load test condition without loop, the traditional 900 ohm source/load
test condition with 2.7 km, 26 AWG loop introduces a frequency dependent loss that affects the measured
frequency response and, hence, the calculated send and receive loudness ratings. ANSI/TIA-470.110-C
provides a circuit schematic and parameter values that can be used for constructing artificial loop sections
that may be subsequently cascade together to create the desired length of artificial cable. At low
frequencies (~100 Hz), these circuit schematics reduce to resistive losses in each of the tip and ring
conductors.
It is a straight-forwarded matter to then calculate the ratio of the voltage delivered to a 900 ohm load at
the end of the loop to the open circuit voltage from the 600 ohm source representing the telephone. The
value is V/Voc = 0.4007, or -7.94 dB. This compares to a ratio of V/Voc = 0.5000 or -6.02 dB for the
case of a 600 ohm source terminated in a 600 ohm load without any loop. So the send voltage delivered
to the 900 ohm termination through the 2.7 km loop by a 600 ohm telephone is 1.92 dB lower than the
voltage it would deliver to a 600 ohm termination without loop. The amount of loss increases only
slightly with frequency below 1000 Hz, but rolls of by about 6 dB at 4000 Hz and 13 dB at 8000 Hz.
For receive we have either a 600 ohm source delivering a signal to a 600 ohm load representing the
telephone without intervening loop or a 900 ohm source delivering its signal through the 2.7 km, 26
AWG loop to a 600 ohm load representing the telephone. At low frequencies (~100 Hz) it is again a
straight-forwarded matter to calculate the ratio of the voltage delivered through the loop to the 600 ohm
load representing the telephone to the open circuit voltage from the 900 ohm source. The ratio is V/Voc
= 0.2671 or -11.47 dB. This compares to a ratio of V/Voc = 0.5000 or -6.02 dB for the case of a 600 ohm
source terminated in a 600 ohm load representing the telephone without any loop. So the receive voltage
delivered to a 600 ohm telephone through the 2.7 km loop from a 900 ohm source, and hence the acoustic
output from the telephone receiver, will be 5.45 dB lower than the voltage that would be delivered by a
600 ohm source without any loop, provided the Voc value is the same in both cases. If the Voc value
differs because different matched load calibration values are specified for the test, the acoustic output of
the receiver will differ by the same amount (assuming receive linearity), and the RLR calculation, which
is a measure of output minus input (loss) will be the same. As with the send case, the amount of loss
increases only slightly with frequency below 1000 Hz, but rolls of by about 6 dB at 4000 Hz and 12 dB at
8000 Hz.
Applying these principals to the calculation of send loudness ratings for one example each of wideband
and a narrowband telephone frequency responses suggests the nominal SLR value for the 600 ohm
without loop test condition should be about 4.5 dB less positive (louder) than for the 900 ohm with loop
case (SLR = 3.5 dB instead of SLR = 8.0 dB). Corresponding calculations for the receive loudness
ratings suggest the nominal RLR value for the 600 ohm without loop test condition should be about 4.5
dB more negative (also louder) than for the 900 ohm with loop case (RLR = -7.5 dB instead of RLR
= -3.0 dB). There does not appear to be a significant bandwidth effect on these delta values when the
appropriate weighting functions and bandwidths are used for the loudness rating calculations.
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