NTIA-Report-80-43

Measu rement of the Effect

of Vehicle Ignition Noise

on Land-Mobile

Voice Channels

w. J. Hartman

u.s. DEPARTMENT OF COMMERCE

Philip M. Klutznick, Secretary

Henry Geller, Assistant Secretary

for Communications and Intormation

June 1980

PREFACE

This work was done by u. S. Department of Commerce,

National Telecommunications and Information Administration,

Institute for Telecommunication Sciences, for the Motor

Vehicle Manufacturers Association of the United States, Inc.,

Detroit, Michigan 48202.

iii

TABLE OF CONTENTS

LIST OF FIGURES

LIST OF TABLES

1. INTRODUCTION

2. TEST PROCEDURES

3. TEST RESULTS

4. DISCUSSION OF RESULTS

5. REFERENCES

APPENDIX: AMPLITUDE PROBABILITY DISTRIBUTIONS

v

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Figure 1.

Figure 2.

Figure Al.

Figure A2.

Figure A3.

Figure A4.

Figure A5.

Figure A6.

Figure A7.

Figure A8.

Figure A9.

Figure AlD.

LIST OF FIGURES

The location of vehicles for the 1979 MVMA tests.

Comparison of the subjective articulation scores (AS

with the objective scores. The straight line would

be perfect agreement.

The APD1s for test 1 at 50 MHz with 1 SAE vehicle.

V(RMS) = -120.6 dBm.

The APD1s for tests 2 and 3 at 50 MHz with 1 super

noisy vehicle. V(RMS) = -100.6 dBm.

The APD for test 4 at 50 MHz with no vehicles.

V(RMS) = -120.4 dBm.

The APD for test 5 at 29 MHz with no vehicles.

V(RMS) = -118.5 dBm.

The APD for test 6 at 50 MHz with 6 SAE vehicles.

V(RMS) = -119.9 dBm.

The APD for test 7 at 29 MHz with 12 SAE vehicles.

V(RMS) = -117.4 dBm.

The APD for test 8 at 50 MHz with 12 SAE vehicles.

V(RMS) = -119.7 dBm.

The APD for test 9 at 50 MHz with 11 SAE and

1 super noisy vehicle. V(RMS) = -102.9 dBm.

The APD for test 10 at 147 MHz with 12 SAE vehicles

V(RMS) = -118.1 dBm.

The APD for system noise through the filter,

amplifier, spectrum analyzer and DM3.

V(RMS) = -121.0 dBm.

LIST OF TABLES

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5

10

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Table 1.

Table 2.

Table 3.

Table 4.

Table 5.

1979 MVMA Tests.

Voice Scores.

Statistical Noise Parameters.

Tabulation for Comparison of the Noise Statistical

Parameters with the Articulation Scores.

Correlation Coefficients for Test 1, 4, 6, 8, and

9 Between the Statistical Noise Parameters and the

Voice Scores.

vii

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MEASUREMENT OF THE EFFECT OF VEHICLE IGNITION NOISE ON

LAND-MOBILE VOICE CHANNELS

w. J. Hartman*

Measurements of the voice intelligibility over landmobile systems in the presence of vehicle noise are presented. These are compared with several statistical noise

parameters obtained from measured amplitude probability distributions.

Key words: Impulse noise, intelligibility, scoring, vehicle noise.

1. INTRODUCTION

Tests were run during April 1979, at the GM proving ground near Milford,

Michigan, to determine the effects of automotive ignition noise on the voice

channel performance of land-mobile radios. The Institute for Telecommunication

Sciences (ITS) participated in these tests by measuring the amplitude probability

distribution (APD) of the noise and making voice recordings for later scoring.

The voice intelligibility scoring was done both subjectively (listener panel) and

objectively (Gamauf and Hartman, 1977). The results of these tests are presented

here.

From the APD, the statistical moments can be obtained and compared with the

voice scoring. Here, we calculate the average V(AVG), the root mean square V(RMS),

and the difference Vd = V(RMS) - V(AVG) for comparison.

2. TEST PROCEDURES

The vehicles, antennas, cables, and receivers were provided by The Motor Vehicle

Manufacturers Association (MVMA). A total of 10 test conditions were used, and these

are described in Table 1. The placement of the vehicles is shown in Figure 1. When

a super noise vehicle (SNV) was used, it was placed in position 1, except for the

test condition #9, when it was placed in position 4. The receiving antenna was

located on the trunk of the test car. The antenna cable was run into a building used

for the test equipment. The APD tests used the output from the antenna cable as an

input signa 1.

*

The author is with the U.S. Department of Commerce, National Telecommunications

and Information Administration, Institute for Telecommunication Sciences,

Boulder, Colorado 80303.
Table 1. 1979 MVMA Tests

Test Schedule

Test No. Frequency Vehicles Signal Level

(dBm)

1 50 MHz 1 SAE -108

2 50 MHz 1 SNV -108

3 50 MHz II -98

4 50 MHz None -108

5 29 ~1Hz II -101

6 50 MHz 6 SAE -108

7 29 MHz 12 SAE -101

8 50 ~1Hz 12 SAE -108

9 50 MHz 11 SAE+SNV -108

10 147 MHz 12 SAE -113

BG1~G

EJ G

8 [~ G

8 G

~3m-+)

G

12

ITESTI CAR

Figure 1. The location of vehicles for the 1979 MVMA tests.

2
For the tests at 50 ~·1Hz, thi s signa 1 was fi rst passed through a tunab1e bandpass filter [Texscan 5 VF 48195-5-CC]1~ then through a fixed (40 dB) gain broadband

amplifier [ENI 411 LA], and into an HP 85588 spectrum analyzer. The 21.4 MHz output

of the spectrum analyzer was then used as input to the noise measuring system, the

DM 3

2. For the 29 MHz and the 147 MHz tests a bandpass filter was not available, but

the rest of the test configuration remained the same.

The DM 3, which was built by the Institute for Telecommunication Sciences for the

Air Force, uses an envelope detector to detect th~ IF output voltage, and quantizes

the output of the detector into 15 discrete levels spaced 6 d8 apart. The count at

each level divided by the total count gives the percentage of time that the envelope

exceeds that level. An internal calibration is available for setting the 6 dB steps.

An external calibration was made using a sine wave from a signal generator.

This signal was substituted at the input to the filter, or the amplifier as appropriate. This technique allows the calculation of input noise levels and serves as a

check on the internal calibration.

The DM 3 has a bandwidth of approximately 1 MHz. The spectrum analyzer was used

to select the narrow band mode, 30 kHz, for the measurements.

For the voice measurements, the phonetically balanced (PB) word lists were played

from a master tape on a lj2-inch recorder. This signal was used to modulate the

transmitter. The audio output of the receiver was recorded on a second identical

recorder. The master tape had 8 50-word PB word groups. For the 10 tests, two word

groups were repeated once and six word groups were used only once.

1. IICertain commercial equipment, instruments, or materials are identified in this

paper to adequately specify the experimental procedure. In no case does such

identification imply recommendation or endorsement by the National Telecommunications and Information Admini.stration, nor does it imply. that the

material or equipment identified is necessarily the best available for the

purpose. II

2. Robert Matheson described the DM 3 in an unpublished draft, "An Instrument to

Measure the Amplitude Probability Distribution of EM Noise.

3
3. TEST RESULTS

The voice tapes were copied, edited, and sent to the U.S. Army Electronic

Proving Ground, Ft. Huachuca, Arizona, for subjective scoring by listener panels.

The tapes were also scored objectively using a modification of the methods

developed by Gamauf and Hartman (1977). The subjective and objective articulation

scnres (AS) for 10 tests are given in Table 2.

The objective scores are plotted against the subjective scores in Figure 2.

The straight line would represent perfect agreement. The correlation coefficient

between the objective and subjective scores is .88.

The calculation of the objective score requires alining the digitized samples

of the master tape with the samples from the tapes with the noise added. In the

earlier study, [Gamauf and Hartman, 1977J this was done using software. For this

study a newly developed hardware alinement procedure was used, greatly decreasing

the cost of obtaining the objective scores.

The APDls are given in the Appendix. The statistical parameters V(average),

V(RMS) and Vd = V(RMS) - V(average) calculated from the APDls are given in Table 3.

Table 2. Voice Scores

Test No. Word Group Subjective Objective

AS AS

1 361 72.5 73.3

2 312 72.7 71.7

3 291 84.7 81.1

4 265 80.2 76.4

5 291 92.7 88.5

6 275 69.7 71.0

7 312 78.5 68. 1

8 305 68.2 69.8

9 214 75.5 66.7

10 265 57.7 61.0

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Figure 2. Comparison of the subjective articulation scores

(AS) with the objective scores. The straight

line would be perfect agreement.

5
Table 3. Statistical Noise Parqmeters

30 kHz Bandwi dth

V(RMS) V(AVG) Vd

Test # Figure # dam darn dB

1 Al -120.6 -122.2 1.6

* 2,3 A2 -lOO~6 -119.9 19.3

4 A3 -120.4 -121 .8 1.4

5 A4 -118.3 -119.7 1.4

6 A5 -119.9 -121 .6 1.7

7 A6 -117.4 -119.0 1.6

8 A7 -119.7 -121.5 1.8

9 A8 -120.9 -1'20.4 17.5

10 A9 -118. 1 -119.4 1.3

Ca1i b. Al0 -121 . 0 -122.4 1.4

*The noise was the same for test 2 and 3.

4. DISCUSSION OF RESULTS

Table 4 contains the statistical parameters together with the articulation

scores for easy comparison. As noted in the previous section, the corre l aticn

between the articulation scores is .88.

It is instructive to compare the noise parameters with the subjective scores

to determine if any of these are good predictors. Several of the tests at 50 MHz

allow a comparison of results because the same frequency and input signal level are

used. Referring to Table 1, we would expect the following ordering (on the basis

of the test condition) of the AS from best score to worst score; #4(no vehicles)

#1(1 SAE), #6(6 SAE) , #8(12 SAE), #9(11 SAE & 1 SNV). The subjective articulation

scores are ordered 4, 9, 1, 6, and 8, and the objective scores are ordered 4, 1,6,

8, and 9. Consequently, the subjective score for test 9 appears inconsistent. For

the five similar tests 1, 4, 6, 8, and 9, the correlations are given in Tqble 5.

The four tests, 4, 1, 6, and 8 with ~espectjvely 0, 1, 6, and 12 SAE vehicles show

decreasing intelligibility (8b.2%, 72.5%, 69.7%, and 68.2%) as expected, with the

6
Tabl e 4. Tabulation for Comparison of the Noise Statistical

Parameters with the Articulation Scores.

Test No. V(RMS) Vd Signal Level Subjective Objective Vehicles

dBm dB (dBm) AS AS

1 -120.6 1.6 -108 72.5 73.3 1 SAE

2 -100.6 19.3 -108 72.7 71 .7 1 SNV

3 -100.6 19.3 -98 84.7 81 . 1 II

4 -120.4 1.4 -108 80.2 76.4 NONE

5 -118.3 1.4 -101 92.7 88.5 II

6 -119.9 1.7 -108 69.7 71.0 6 SAE

7 -117.4 1.6 -101 78.5 68.1 12 SAE

8 -119.7 1.8 -108 68.2 69.8 12 SAE

9 -102.9 17.5 -108 75.5 66.7 11 SAE+SNV

10 -113 57.7 61.0 12 SAE

Table 5. Correlation Coefficients for Tests 1, 4, 6, 8, and 9 Between

the Statistical Noise Parameters and the Voice Scores

Subjective score

Objective score

V(RMS)

-.19

-.75

7

V(AVG)

.10

.03

.25

-.74
largest change observed between no vehicles and 1 vehicle. None of the statistical

noise parameters appear to be a good predictor of the subjective AS although V(RMS)

exhibits some correlation with the objective AS (significant at the 5% level).

The tests using a SNV, are more difficult to interpret. Previous results

(Spaulding, 1976) indicate that impulsive noise is less harmful than Gaussian noise

to voice intelligibility for the same values of V(RMS). However, comparing tests 1

and 2, and 8 and 9, we see that V(RMS) for the replacement of anSAE vehicle with

an SNV produces a much larger V(RMS). It should be noted that for both pair~ the

subjective scores are higher when the SAE vehicle is replaced by an SNV, while the

objective scores are lower in both cases.

5. REFERENCES

Gamauf, K. J., and W. J. Hartman (1977), Objective measurement of voice channel

intelligibility, FAA Report No. FAA-RD-77-153, October.

Spaulding, A. D. (1976), Man-made noise: The problem and recommended steps

toward solution, Office Of Telecommunications Report OT 76-85. (NTIS

Access No. PB 253 745/AS).

8
APPENDIX AMPLITUDE PROBABILITY DISTRIBUTIONS

Figuras Althrough A10 show the APD1s for the test conditions 1-10 and one of

the calibration runs, respectively. The sharp rise at the lower percentages in

Figures A2 and A8 is typical of impulse noise. Each of these curves is normalized

to the V(RMS) for that test condition and this V(RMS) is given in the figure

caption. Note that tests 2 and 3 had the same noise condition.

9
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17
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USCOMM . ERL

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V(RMS) = -118.1 dBm.

18
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spectrum analyzer and DM3. V(RMS) = -121.0 dBm.

19

FORM NTIA-29

(4-80)

U.S. DEPARTMENT OFCOMMERCE NAT'L. TELECOMMUNICATIONS AND INFORMATION ADMINISTRATION

BIBLIOGRAPHIC DATA SHEET

4. TITLE AND SUBTITLE

1. PUBLICATION NO.

NTIA Report 80-43

2. Gov't Accession No. 3. Recipient's Accession No.

5. Publication Date

Measurement of the Effect of Vehicle Ignition Noise on Land-Mobile Voice Channels

7. AUTHOR(S)

W. J. Hartman

8. PERFORMING ORGANIZATION NAME AND ADDRESS

U. S. Department of Commerce

NTIA/ITS-2

325 Broadway

Boulder, CO 80303

11. Sponsoring Organization Name and Address

Motor Vehicle Manufacturers Association

of the United States, Inc.

Detroit, MI 48202

14. SUPPLEMENTARY NOTES

June 1980

6. Performing Organization Code

NTIA/ITS-2

9. Project/Task/Work Unit No.

9104387

10. Contract/Grant No.

ITS 7925-C2.52

12. Type of Report and Period Covered

NTIA Report

13.

15. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant bibliography or literature

survey, mention it here.)

Measurements of the noise intelligibility over land-mobile systems

in the presence of vehicle noise are presented. These are compared with

several statistical noise parameters obtained from measured amplitude

probability distributions.

16. Key Words (Alphabetical order, separated by semicolons)

Impulse noise; intelligibility; scoring; vehicle noise.

17. AVAILABILITY STATEMENT

I&l UNLIMITED.

o FOR OFFICIAL DISTRIBUTION.

18. Security Class. (This report)

Unclassified

19. Security Class. (This page)

Unclassified

20. Number of pages

32

21. Price:

* u.s. GOVERNMENT PRINTING OFFICE: 1980-0-679-075/478