Telecommunications Industry Association TR41.3.5-13-08-006-R1
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Source
Contact
Document Cover Sheet
ANSI/TIA-PN-470.112
Proposed Annex on Determination of Nominal Loudness Rating Values
Whitesell Consulting LLC
Stephen R Whitesell
2 Shannon Ct
Howell, NJ 07731-8919
Phone: 732 751 1079
Fax:
Email: swhitesell@ieee.org
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(Select one)
TR-41.3.5
X For Incorporation Into TIA Publication
For Information
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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
Determination of the nominal SLR and RLR values for measurements using a 600 ohm source or termination impedance without intervening loop has been a major issue in the development of ANSI/TIA-
PN-470.112. Contributions TR41.3.5-13-04-014a-L, TR41.3.5-13-04-014b-MR1, and TR41.3.5-13-04-
015-L provided the analyses that led to setting the nominal SLR = 3.5 dB and RLR = -7.5 dB. Both cases represent a 4.5 dB shift from the nominal values for the same telephone measured using a traditional 900 ohm source or termination impedance and 2.7 km (9 kft) loop of 26 AWG cable.
This contribution proposes the text for a new informative Annex D to be inserted in ANSI/TIA-PN-
470.112. It provides an explanation of how the nominal SLR and RLR values were derived, including an analysis of the effects of the test configuration differences on the V/V
OC
ratio, where V is the voltage delivered to the termination and V
OC
is the open circuit voltage of the telephone for send measurements.
Conversely, V is the voltage delivered to the telephone and V
OC
is the open circuit voltage of the source used for receive measurements. It also includes embedded spreadsheets showing how knowledge of this information may be applied to arbitrary send and receive frequency sensitivity curves to determine the desired SLR and RLR values. v1.0 – 20050426

Telecommunications Industry Association TR41.3.5-13-08-006-R1
The send and receive loudness ratings for this Standard are measured without any intervening cable or loop between the telephone set and the specified 600 ohm source or termination impedance. The traditional method of measuring transmission performance for an analog telephone is to use a 900 ohm source or termination impedance and measure for three loop conditions: 0, 2.7, and 4.6 km of 26 AWG cable (see ANSI/TIA-470.110-C).
In addition, this Standard uses the wideband loudness rating calculation equations and weighting functions described in Annex B. A comparison of the information provided there to the equations and weighting functions for narrowband loudness rating calculations provided in Annex B of ANSI/TIA-
470.110-C reveals the following differences:
1.
The narrowband SLR and RLR calculations are limited to band numbers 4-17 covering the frequency range from 200 Hz to 4000 Hz.
2.
Each of the weighting factors in that frequency range differs from its wideband counterpart by 0.3 dB.
3.
There is a correction factor of 1.76 dB = 10 log
10
(900/600) that gets subtracted from the send sensitivities and added to the receive sensitivities when measurements are made using 900 ohm source or load impedances instead of 600 ohms.
Furthermore, examination of the weighting factors indicates that the wideband frequencies above 4000 Hz add virtually nothing to the calculated SLR and RLR values. At the low frequency end, the 160 Hz data point makes a small contribution, more so to receive than send, and the lower frequencies add virtually nothing to the overall loudness. So the narrowband calculation covers the frequency range that makes the most significance contribution to the overall loudness.
Based on the above information, the goal in establishing the nominal SLR and RLR values for this
Standard was that a telephone having those nominal values would also have a nominal SLR value of 8 dB and a nominal RLR value of -3dB as specified in ANSI/TIA-470.110-C when measured in the traditional manner on a 2.7 km loop of 26 AWG cable with a 900 ohm source or termination impedance. The 1.76 dB correction factor mentioned above should be included in the calculations for the 900 ohm tests and excluded for the 600 ohm tests.
This annex provides an analysis of the effects of the 600 ohm vs. 900 ohm source and termination impedance differences and the inclusion of 2.7 km of 26 AWG cable on the calculated SLR and RLR values for an idealized telephone represent by a 600 ohm impedance. This analysis then allows mapping the nominal SLR and RLR values determined using the traditional 900 ohm tests with 2.7 km loop to appropriate values using the 600 ohm tests without loop specified in this Standard.
D.1
A NALYSIS OF E FFECTS OF T EST C ONFIGURATION D IFFERENCES
The test configurations of interest are shown in Figure D.1 for the send case and in Figure D.2 for the
receive case. The telephone is represented as a 600 ohm resistive source for send or as a 600 ohm resistive termination for receive. For the measurements in this standard, the 600 ohm telephone is connected without intervening loop to a corresponding 600 ohm termination for send or a 600 ohm source for receive. For the traditional test method, the 600 ohm telephone is connected through 2.7 km loop of
26 AWG cable to a 900 ohm termination for send or a 900 ohm source for receive. The 2.7 km loop is normally composed of a 0.914 km (3 kft) cable section and a 1.83 km (6 kft) cable section for testing purposes. Schematic information for modeling these loop sections is provided in ANSI/TIA-470.110-C.
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Telecommunications Industry Association TR41.3.5-13-08-006-R1
600 600
Voc V 600 Voc
0.914 km
(3 kft)
26 AWG
Cable
1.83 km
(6 kft)
26 AWG
Cable
V 900
Voc
Phone Term
This Standard
600
V 600
Phone Loop
Traditional Test Method
Figure D.1 – Send test configurations
900
Voc
0.914 km
(3 kft)
26 AWG
Cable
1.83 km
(6 kft)
26 AWG
Cable
Term
V 600
Source Phone Source Loop Phone
This Standard Traditional Test Method
Figure D.2 – Receive test configurations
For send, V
OC
is a function of the design and transduction efficiency of the telephone and of the input sound pressure as measured at MRP. For a given input sound pressure, it is independent of whether the telephone is tested using the 600 ohm termination without loop or the 900 ohm termination with 2.7 km loop. The difference in SLR for the two test configurations thus depends on the relative value of the voltage V delivered to the termination for each case. The analysis is facilitated by determining the V/V
OC ratio on a dB basis.
For receive, the acoustic output of the receiver as measured at the ERP is a function of the design and transduction of the telephone and of the voltage V delivered to the telephone by the test configuration.
V
OC
is normally established by specifying a “nominally loaded” signal level that is determined with the source terminated in a resistor equal to the source impedance. The load resistor is then removed and the source is connected to the test circuit. V
OC
is thus twice the specified “nominally loaded” signal level. If
V
OC
is held the same for the two test configurations, the difference in RLR will depend on the value of V delivered to the telephone assuming it has linear receive input/output characteristics. Even if the value of
V
OC
is chosen to be different for the two test configurations, it is the V/V
OC
ratio that controls the signal level delivered to the telephone. The -30 dBV nominally loaded signal level specified in this standard for the 600 ohm without loop test condition has been chosen to provide approximately the same voltage to the telephone as it would receive when tested using a -25 dBV nominally loaded level from a 900 ohm source with a 2.7 km loop, so any non-linearity effects in the telephone are minimized.
For the 600 ohm case without loop as specified in this standard, the determination of the V/V
OC
ratio on a dB basis for both send and receive is a simple voltage divider calculation that yields -6.02 dB independent of frequency. The schematic information provided for the artificial cable sections in ANSI/TIA-470.110-
C may be used with circuit simulation software to determine V/V
OC
for the 900 ohm with loop case. The results for both send and receive on a dB basis are summarized at the R10 frequencies used for loudness
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Telecommunications Industry Association TR41.3.5-13-08-006-R1
R10
Frequency
(Hz)
630
800
1000
1250
1600
2000
2500
3150
100
125
160
200
250
315
400
500
4000
5000
6300
8000
10000
rating calculations in Table D.1. The differences relative to the 600 ohm without loop case are also
summarized in the table. The results are presented graphically in Figure D.3
Table D.1 – Test configuration loop loss effects
600 Ohm without Loop
-6.02
-6.02
-6.02
-6.02
-6.02
-6.02
-6.02
-6.02
-6.02
-6.02
-6.02
-6.02
-6.02
-6.02
-6.02
-6.02
-6.02
-6.02
-6.02
-6.02
-6.02
20 log
10
(V/V
OC
) (dB)
900 Ohm with Loop
Send
-7.95
-7.95
-7.96
-7.97
-7.98
-8.01
-8.05
-8.11
-8.20
-8.34
-8.55
-8.87
-9.33
-9.98
-10.83
-11.91
-13.20
-14.68
-16.31
-18.04
-19.93
Receive
-11.47
-11.48
-11.48
-11.49
-11.51
-11.53
-11.57
-11.63
-11.72
-11.86
-12.07
-12.39
-12.85
-13.50
-14.35
-15.43
-16.72
-18.21
-19.84
-21.58
-23.39
900 Ohm vs. 600 Ohm Difference
Send Receive
-1.93
-1.93
-1.94
-1.95
-1.96
-1.99
-2.03
-2.08
-2.18
-2.32
-2.53
-2.85
-3.31
-3.96
-4.81
-5.89
-7.18
-8.66
-10.29
-12.02
-13.81
-5.45
-5.45
-5.46
-5.47
-5.49
-5.51
-5.55
-5.61
-5.70
-5.84
-6.05
-6.37
-6.83
-7.48
-8.33
-9.41
-10.70
-12.19
-13.82
-15.56
-17.37
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Telecommunications Industry Association
0
-5
-10
TR41.3.5-13-08-006-R1
-15
-20
600 Ohm
900 Ohm Send
900 Ohm Receive
-25
100 1000
Frequency (Hz)
10000
Figure D.3 – Test configuration loop loss effects
D.2
A PPLICATION TO L OUDNESS R ATING V ALUES
The information in Table D.1 can be used as the basis for determining what the nominal SLR and RLR
values measured using the 600 ohm without loop method should be in order for the same telephone to have SLR = 8 dB and RLR = -3 dB when measured using the 900 ohm with loop method. The process is as follows:
1.
Obtain send and receive frequency response sensitivity data for a wideband telephone using the
600 ohm without loop method. This data may be measured or even arbitrarily assigned.
2.
Use the data in the 900 Ohm vs. 600 Ohm Difference columns of Table D.1 to obtain
corresponding send and receive frequency response sensitivity data for the 900 ohm with loop test method.
3.
Calculate SLR for both sets of send frequency response data and RLR for both sets of receive frequency response data, being sure to include the 1.76 dB correction factor for the 900 ohm with loop case as discussed above.
4.
The difference in calculated SLR and RLR values are the adjustments that need to be made to the
SLR = 8 dB and the RLR = -3 dB values when using the 600 ohm without loop test method.
An example of the above calculation applied to an arbitrary send sensitivity curve that fits well within the
frequency response template of Figure 5 is shown in Figure D.4. The calculations are included in a
spreadsheet embedded with the figure. An SLR value of 3.6 dB for the 600 ohm without loop test method corresponds to SLR = 8 dB for the 900 ohm with loop test method.
A similar calculation for an arbitrary receive sensitivity curve that fits well within the frequency response
template of Figure 6 is shown in Figure D.5. The calculations are likewise included in a spreadsheet
embedded with that figure. An RLR value of -7.6 dB for the 600 ohm without loop test method corresponds to RLR = -3 dB for the 900 ohm with loop test method.
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Telecommunications Industry Association TR41.3.5-13-08-006-R1
Similar calculations made for additional send and receive sensitivity curves during the preparation of this
Standard were consistent in showing an approximately 4.5 dB difference in both the SLR and RLR values for the two test methods. The contributions containing these calculations are available in the FTP folder for the May 2013 meeting of TR-41.3.5 on the TIA web site.
0
-5
600 Ohm without Loop (SLR = 3.6 dB)
900 Ohm with Loop (SLR = 8.0 dB)
-10
-15
-20
-25
-30
100 1000
Frequency (Hz)
10000
Figure D.4 – SLR calculation example
25
20
15
10
5
0
-5
100
600 Ohm without Loop (RLR = -7.6)
900 Ohm with Loop (RLR = -3.0)
1000
Frequency (Hz)
10000
Figure D.5 – RLR calculation example
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