Naval Submarine Medical Research Laboratory

NSMRL REPORT 1186 30 JULY 1M6

AD-A275 008

VEDLICAL CO~

EVALUATION OF COMMUNICATION DURING ACTIVE SONAR

TRANSMISSIONS WITH A SPEECH-RECOGNITION MODEL

DT I C7 LLynne Marshal,

""T: Thomtas E. Hanna

"LECTE and

S" JAIN 2 11994 Chaslav V. Pavlovic

• 94-01798

Released by

P. K. Weathersby, CAPT, MSC, USN

Commanding Officer

Naval Submarine Medical Research Laboratory

Approved for public release; distrfil utited

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EVALUATION OF COMMUNICATION DURING

ACTIVE SONAR TRANSMISSIONS WITH A

SPEECH-RECOGNITION MODEL

Lynne Marshall, Ph.D. and Thomas E. Hanna, Ph.D.

Naval Submarine Medical Research Laboratory

Chaslav V. Pavlovic, Ph.D.

University of Iowa

Naval Submarine Medical Research Laboratory

NSMRL Report 1188

Naval Medical Research and Development Command

Naval Sea Systems Command (PMO 424) Accesio; ',7

Program Executive Office Surface Ship ASW Systems

Task No. SSAS-91-77A01R2 NTISC A'.!

By.....

Released bv

P.K. Vveatnersoy, %iAr i, ivi.-C, USN ACommanding Officer

Approved for public release; distribution unlimited
SUMMARY PAGE

PROBLEM

To determine whether intense tones in the frequency region around 1000 Hz might affect

speech recognition in background noises similar to those found on ships.

METHOD

The Speech Intellibibility Index (SII) was used to quantify the expected acoustic interference

of tones around 1000 Hz and pink noise. The tones simulate an active-sonar system that would

radiate back through the ship's compartments. The pink noise simulates shipboard background

noise.

FINDINGS

A speech-recognition model predicted that speech-recognition could remain high in the presence of the intense tonal maskers, but that speakers would have to raise their voices, often to a

shout, in order to maintain intelligibility. Results with actual speakers and listeners verified this

prediction.

APPLICATION

Intermittent,. intense tones should not create undue problems for speech communication. The

tones in this study had a 6-sec duration with a 24-sec rest between tones, as might be used for an

active-duty cycle. If the tones were on for longer durations, however, listeners might have difficulty maintaining the high voice levels required for communication. In addition, if listeners are

working on complex tasks or under stress, their speech understanding might decrease markedly.

Other factors that could markedly decrease speech understanding, especially in combination with

high levels of background noise and high levels of task complexity, include a listener with a hearing loss, a speaker with unclear speech, or a poor transmission system distorting the speech signal.

ADMINISTRATIVE INFORMATION

This research was carried out under a task plan entitled, "Development of acoustic

habitability standards for ships' spaces subjected to intense tones" and was funded by Program

Executive Office Surface Ship ASW Systems Task No. SSAS-91-77A01R2 dated 14 December

1990 "AN/SYQ-1 Frequency Array testing", Naval Sea Systems Command PMO 424. The

views expressed in this article are those of the authors and do not reflect the official policy or

position of the Department of the Navy, Department of Defense, or the U.S. Government. This

report was approved for publication on 30 July 1993, and designated as NSMRL Report 1188.

ii
ABSTRACT

Predictions using the Speech Intelligibility Index (SIl) are reported for speech recognition in

tonal and broadband noise. Three levels of background pink noise (60, 65, and 70 dBA) were

used for the SII. Tones in the frequency range around 1000 Hz at 77, 83, and 89 dB SPL were

added to the background pink noise. The speech spectra were for four different vocal efforts

(normal, raised, loud, and shouted). The simulated listeners for most of the predictions were

assumed to have normal hearing. A hearing loss was also included for a subset of predictions. If

"barely adequate" speech recognition is used as a criterion, the effects of the background noise

can be overcome by increasing the vocal effort of the speaker, often to a shout.

Illi0
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iv
EVALUATION OF COMMUNICATION DURING ACTIVE SONAR TRANSMISSIONS

WITH A SPEECH-RECOGNITION MODEL

The purpose of the present investigation was increases, there are two changes in the speech

to estimate the extent to which active sonar spectra. The first is that the overall level insounds from a new sonar system would inter- creases. The second is that the spectral shape

fere with speech recognition on ships. Speech- changes; there is more high-frequency empharecognition performance was modeled using sis with increased vocal effort. Thus, it is imthe Speech Intelligibility Index (ANSI, 1992). portant to include the effect of vocal effort in

The Speech Intelligibility Index (SII, which estimating speech understanding in backwas formerly known as Articulation Index, or ground noise.

AI) is the proportion of the total speech information reaching the ear of the Pearsons (personal communication, 1988) suglistener, with each frequency band weighted gested (based on work under contract to the

by its relative importance. The maximal value Environmental Protection Agency) that peoof the SII (1.0) means that all acoustic infor- pie raise their voice to maintain 95% correct

mation is present; the minimal value (0.0) sentence recognition, which is equivalent to

means that no acoustic information is present. an SII of approximately 0.45. In general, the

Similarly, a value of 0.5 means that half of the lower cut-off for barely adequate communicainformation is present. As a general guideline, tion is considered to be 0.45 or 0.46. At this

"excellent" speech understanding occurs for SII, scores for single one-syllable words out of

Slls above 0.75, "good" is between 0.6 and context are considerably lower (around 70% cor0.75, "fair" is between 0.46 and 0.6, "poor" is rect) than for sentences. Thus, communication

between 0.3 and 0.45, and below 0.3 is "bad" situations that depend on single words out of

(IEC, 1988). context require higher SIls.

In a noise background, the proportion of the In the present paper, we provide SlIs at three

speech that is above the noise determines the background levels of a tonal complex used to

SII and, thus, speech understanding. A funds- simulate the active sonar of interest. Four vomental effect of noise on speech production is cal efforts are presented ranging from normal

that vocal effort increases with increasing to shouted speech. The effects of hearing loss

background noise levels. As vocal effort also are briefly discussed.

1
Method The speech and noise spectra were divided

into 18 1/3-octave bands (with center frequenThe modeled speech signal was the average cies from 160 to 8000 Hz) for this analysis.

speech spectrum of male and female speech as The weighting for the relative importance of

measured in free field, one meter from the each frequency band in the speech signal is

talkers' lips for four vocal efforts - normal, dependent on the speech materials used. 1 The

raised, loud, and shout (Pavlovic, Rossi, and importance function for this analysis was the

Espesser, 1990). For normal, raised, loud, frequency-band weightings averaged across

and shouted vocal efforts, the overall levels of several types of speech materials (e.g., nonspeech are 62.4 dB SPL, 68.3 dB SPL, 74.8 sense syllables, monosyllabic meaningful

dB SPL, and 82.3 dB SPL respectively, words, easy running speech) (Pavlovic, 1987).

The speech spectrum undergoes two addi- The background noise used in our SII calculational changes in the hearing process. The tions had two components. The first was pink

first is that the head and external ear (pinna noise,2 which approximates the measured

and ear canal) alter the spectrum via their reso- backgrounds in many compartments of surnance characteristics (i.e., transfer function). face ships. Three levels of pink noise, 60, 65,

The second is that, in the inner ear, energy and 70 dBA were used. The levels 60 dBA

from some frequency bands may spread to oth- and 65 dBA are maximum permissible levels

ers, especially at higher intensity levels (i.e., of continuous broadband noise on Naval vesmasking). The same factors affect the noise sels for category A-12 (talkerspectrum. The present model uses a free-field- listener distance 6 feet or greater) and C (quiet

to-eardrum transfer function (Bentler and essential; e.g., sonar and medical) spaces, rePavlovic, 1989), and the spread of masking spectively (CNO, OPNAVINST 9640.1,

across bands was calculated according to Lud- 1979). The 70 dBA level is specified both for

vigsen (1985). A-3 spaces, where talker-listener distances are

less than three feet (e.g., small offices), and

At higher levels of speech input, increases in for areas where the primary consideration is

the speech level do not increase the speech comfort (e.g., berthing areas and wardrooms).

recognition at the same rate as at lower levels. The second background noise component was

In the current model, a decreasing proportion pure tones at the frequencies of 720, 800, 880,

of the speech energy contributed to the SII at 960, 1040, and 1120 Hz, which simulated achigher levels (above approximately 72 dB tive sonar pings. The model assumed that one

SPL). of these tones was always present, with each

being equally represented.

1 Speech understanding is influenced by the redundancy of the speech; the greater the speech redundancy, the

easier it is to understand and the less it will be degraded in difficult listening situations. The frequency

distribution of the usable informational content of the signal also is affected by the speech redundancy. For

example, the frequency band with the highest weight in the importance function for a typical set of nonsense

syllables is 2500 Hz while for a typical sample of running speech is 450 Hz. See Pavlovic (1987) for more

details.

2 Pink noise has a continuous frequency spectrum with spectrum level decreasing at 3 dB/octave, which has the

result of having equal energy within a bandwidth proportional to the center frequency of the band.

2
The hypothetical listeners for our calculations whether to watch the speaker. Although

had normal hearing (0 dB HL thresholds at all watching the speaker would have been a good

frequencies) and were listening binaurally, strategy because visual cues aid speech understanding, the subjects looked at the answer

Speech-recognition data also were collected sheet instead of the talker.

on Navy enlisted personnel who were in the

laboratory as subjects for habitability studies Testing occurred over three sequential days.

on the effects of the active-sonar pings. All On each of the three days, the subject read the

had normal hearing thresholds (less than or same list, but the word order was varied on

equal to 15 dB HL from 125 through 8,000 each day. On the first day, the test was adminHz). Five or six subjects lived in the labora- istered in the room with no additional noise

tory at the same time. For the speech tests, added (roughly in the 46-51 dBA average

each subject was the speaker for one 50-word range). On the second day, 60 dBA pink noise

list of the Modified Rhyme Test (Kreul et al., was added to the room. On the third day, both

1968). The monosyllabic words take the form the 60 dBA pink noise and the active-sonar

of consonant-vowel-consonant (e.g., "bad"). pings at the particular level

The test has a six-alternative, closed-set test assigned to that subject group were present.

format in which, for each test item, the lis- For two groups, two additional days of testing

tener has six words to choose from (the test took place to assess learning effects. Day 4

word and five foils, which differ from the test was the pink-noise condition (like Day 2), and

word by either the initial or final consonant). Day 5 was a repeat of Day 1, with no additional noise added to the room.

Each subject practiced the assigned list by

reading it aloud to the experimenter. Any mis- Results

pronunciations were corrected during the practice time. During the test, the talker used the A. SI and pings.

phrase, "Mark , ___, and - please," us- SINS, assuming normal-hearing listeners, for

ing connected speech with three words from 60 dbA background noise are shown in Figure

the list to approximate normal speaking condi- 1 (left panel) (the right panel shows a simutions. For each list, one subject was the talker, lated hearing loss, which will be discussed in

and the other subjects were the listeners. The the next section). SIls for 65 and 70 dBA

talkers were given no specific instructions background noise are shown in Figure 2.

about vocal effort, but rather were asked to (All SII values also are included in tabular

speak normally. Most, however, tended to form in the Appendix). Each panel of the figspeak more slowly and loudly with more pre- ures shows SIls for the pink noise alone and

cise pronunciation when reading the word with three levels of tones - 77 dB SPL 83 dB

lists to the group in the test situation than they SPL, and 89 dB SPL. The speech spectra are

did in informal conversations, for normal, raised, loud, and shouted speech.

Details of the physical and acoustical charac- In order to maintain barely adequate speech

teristics of the test room are given in communication (i.e., SII= 0.46 or greater)

Sylvester (1993). Both talkers and listeners in a 60 dBA noise background (Figure 1,

were seated on their beds during the testing. left panel), speakers must use a raised voice.

The subjects were given no instructions about With 77, 83, or 89 dBA tones added to the

3
background noise, they must speak loudly. We know of no recently published studies of

The speech levels predicted from the S1 the hearing levels of officers, but highmodel are consistent with observed speech frequency hearing-threshold elevations of

levels of talkers during a speech communica- this magnitude are found among the enlisted

tion task. active-duty population (NEHC, 1990).

In order to maintain barely adequate speech Figure 1 (right panel) shows the effect of the

communication in the 65 dBA broadband simulated hearing loss. As expected, the SlIs

noise background (Figure 2, left panel), the are lower for the listener with hearing loss.

speaker must use a raised voice, and, when Also, there is less improvement with inthe tones are added at 77 and 83 dB SPL, creased vocal effort if the listener has a hearmust speak loudly. With the addition of an 89 ing loss. The high-frequency acoustic informadB SPL tone, the speaker must shout. In 70 tion that is available to the normal-hearing

dBA background noise, the speaker must listener at increased vocal efforts is not availspeak loudly, and, the addition of the tone (at able to a listener with a high-frequency hearall three levels) requires the speaker to shout. ing loss. For our simulated listener with

hearing loss, the loss at 4000-5000 Hz was the

B. Effect of hearing loss on SII predominant cause of the decreased SlIs.

The effects of a hearing loss also were mod- (Band-by-band speech-to-noise ratios

eled. Thresholds of 20, 30, 35, 40, 55, 90, and illustrating this effect are given in the Appen90 dB HL at 0.5, 1, 2, 3, 4, 6, and 8 kHz, re- dix in Table AP-V.) Noise-induced hearing

spectively, were modeled as a simple loss, which is the most frequent cause of

attenuation (change in threshold levels), as hearing impairment in the Navy, typically is

per the draft ANSI standard (ANSI, 1992). maximal at 4000 Hz. As can be seen in Figure

EFFECTS OF TONE IN NOISE ON SII AT

FOUR VOCAL EFFORTS I1I I I 1 I I

1.0 BACKGROUND NOISE: 60dBA BACKGROUND NOISE: 6Od8A

with HEARING LOSS

-94 - ,.p ~.

..11H ... •~". r0 ""ir

"Poor"

. .............................

-LOUD"

0n &-A N4&M

O 77 83 89 0 77 83 89

TONAL MASKER LEVELS (dB SPL)

Figure 1. SIIS for normal-bearing listeners (left panel) and a hearing loss acceptable for US. Naval officers

(right panel). The background noise in both cases is 60 dBA pink noise with a tonal masker (1000-Hz

region) added at 77, 83, and 89 dB SPL An 511 of 0.46 is considered barely adequate communication.

4
EFFECTS OF TONE IN NOISE ON S!1 AT

FOUR VOCAL EFFORTS

1. 8CKGRMt.C NOI4. 6&SAt 1ýMLR0 NOISE 70d8A'

9 - "ExjakW

.7o "Gooo

.6 .- ....... ... .... .......

0.--0 LOUD

A--A NOtJ

a 77 83 89 0 77

TONAL MASKER LEVELS (dB SPL)

Figure 2. SlIs for normal-hearing listeners in 65 (left panel) and 70 (right panel) dBA pink noise. As in

Figure 1, a tonal masker (1000-Hz region) is added at 77, 83, and 89 dB SPL

1, this hearing-impaired listener requires addition, there is variability among the indigreater vocal effort from the speaker to achieve vidual listeners' performance, especially for

an S11 comparable to a normal-hearing lis- hearing-impaired listeners. That is, it is well

tener. Note that in the 60 dBA background known that some hearing-impaired individunoise used in our simulations, a normal-hear- als have much poorer speech recognition than

ing listener needs a raised voice level, but the others with simliar amounts of hearing loss.3

hearing-impaired listener needs a loud voice These individual differences may well be aclevel for barely adequate communication, counted for by differences in spread of masking. For example, Dubno, He, Schaefer, and

We did not incorporate the increase in Ahlstrom (1992) found that taking into

upward spread of masking that accompanies account individual amounts of spread of maskincreasing hearing loss (as modeled by Lud- ing for SII calculations greatly improved the

vigsen, 1985, and Humes, Espinoza-Varas, ability to accurately predict the relationship

and Watson, 1988) because there is much between SII values and speech-recognition

individual variability in the size of this effect, scores. Accurately predicting both mean data

and there is no consensus on appropriate mod- and the range of performance for hearingeling of hearing loss. Therefore, our calcula- impaired listeners remains to be done.

tions are an upper limit on the SII, and the

performance of groups of hearing-impaired

listeners actually would be expected to be

somewhat poorer than we have shown. In

3 The audiogram describes only one component of a hearing loss. It is not surprising that individuals with

similar audiograms differ in other aspects of hearing such as frequency discrimination and uncomfortable

loudness levels.

5
Table 1

Word-recognition scores for seventeed subjects in three background noises. The

numbers in parentheses below the scores are standard errors of the mean.

Pink noise (60 dBA) +

Ambient room noise Pink noise (60 dBA) 89 dB pings

90.1% 82.7% 78.6%

(1.0) (1.1) (1.7)

C. Actual speech-recognition scores with 89 1 for "quiet" and Day 2 for "pink noise") from

B the average. This correction factor was added

Word-recognition scores are given in Table 1 to the average score for the seventeen subfor the seventeen subjects who listened in the jects. The correction factor was 2% for ambipresence of 89 dB pings. Individual scores ent noise only (Day 1) and 1.8% for the pink

were computed for each list, and all the scores noise (Day 2).

from each individual for one day (one condition) were averaged. Then the scores for all As the signal-to-noise ratio decreased, the

the subjects on each day were averaged, word-recognition scores decreased, as exBecause these were essentially unpracticed pected. They would have decreased more

talkers/listeners, practice effects were seen as except that the speakers increased their vocal

determined by comparisons of the scores on effort as the background noise increased. In

Days 2 and 4 (pink noise) and Days 1 and 5 no condition were the word-recognition

("quiet;" i.e., ambient room noise) for the two scores even close to perfect. The primary reagroups in which scores were measured for son probably is that the listeners were

five, rather than just three, days. The use of a always listening in a noise background at levclosed-set test eliminated the listener effects els sufficient to mask portions of the speech.

due to learning the speech materials. Another

factor that affects listeners, however, is learn- Our impression is that factors such as regional

ing to listen in particular acoustic conditions accents and inattention influenced few individor becoming accustomed to a talker's speech ual scores and thus had a minimal effect on

pattern. Many of the talkers spoke more the mean scores.

clearly and at higher levels as they became

more practiced. In order to correct for learn- The relative decrements across conditions is

ing effects, we decided to reference the scores consistent with the trend predicted by the SII

to the third day (ping day). A correction factor analysis. The exact decrement in percent corfor learning was determined by averaging the rect cannot be predicted from the SII values

scores for the two days that had the same because the transfer function between SII and

condition (Days 2 and 4, and Days 1 and 5), percent correct for our particular set of speakusing the data for the two groups (twelve ers and speech materials is unknown.

subjects) that were tested across five days,

and then subtracting the difference between

the initial test for a particular condition (Day

6
Conclusions (3) Speech transmitted through communication systems (which often are band-limOur conclusion is that, given the low duty cy- ited and distorted) often results in lower

cle (20%) of the active sonar, (i.e., on for 6 speech recognition. If speech underseconds, off for 24 seconds), speakers probably standing in an area is already only "barely

can compensate fbr the interference of the adequate" due to background noise levels,

tones, even at 89 dB, by increasing the vocal distortions in the speech signal over comeffort, often to a shout, while the active sonar munication systems can easily decrease

is activated. If the sonar had a higher duty cy- speech understanding to unacceptable levcle, our conclusion would become more con- els. In addition, the talker may be commuservative because people would be required to nicating from a relatively quiet

maintain greater vocal effort for longer peri- environment to the listener's noisy enviods of time. Not only might they be unwilling ronment and may not adequately compento maintain a high level of vocal effort over sate for the low signal-to-noise ratio in the

long periods of time, but they also would be- listener's space.

come hoarse, with a resultant inability to maintain the required vocal intensity. (4) These SIs assume that the listener is

able to give full attention, both mentally

For particular applications, there are other fac- and visually, to the talker. If performing a

tors that need to be considered. All of these complex task or several tasks simultanwould result in a more conservative conclusion. eously (i.e., high cognitive load or divided

attention tasks), or if performing under

(1) We have assumed that the talkers stress, speech understanding could be lowspeak clearly and distinctly. Presumably, ered. Also, in stressful situations, the talkeven if a speaker's actual speaking style is ers' speech may deteriorate; they may

less clear, training can improve speech speak more rapidly and less clearly. If

clarity in noisy backgrounds. these conditions are likely to occur in

particular environments, a higher S11

(2) Our recommendations assume that all may be required for reasonably good

listeners have normal hearing. However, communication.

hearing losses that are acceptable according to Navy standards will lower the SIls (5) For these reasons, a more stingent

if the hearing loss is sufficient to filter out requirement for speech should be considspeech acoustical information. In addition, ered if understanding must be quick and

many listeners with hearing losses also accurate during the six-second active-sohave more upward spread of masking than nar interval. The importance of good

predicted by this S11 model. The effective speech recognition has been recognized

result is greater perceived noise for the by the Chief of Naval Operations, who

hearing-impaired listeners and thus lower specified that "direct speech communicaSlIs. The actual hearing levels of person- tion must be understood with minimal ernel using particular spaces should be taken ror and without need for repetition" in

into account in determining whether com- Category A spaces (OPNAVINST 9640.1,

munication in a particular space will be 1979). Unfortunately, this description is

adequate. incongruent with the permissible back7
ground noise levels in this same docu- hearing loss. I. Model and retrospective

ment. The noise levels are too high to evaluation. Journal of the Acoustical Socipermit such good speech recognition. ety of America, 83, 188-202.

Acknowledgments IEC. (1988). The objective rating of speech

intelligibility in auditoria by the "RASTI"

Yvonne Masakowski helped with the plan- method (IEC 268-16).

ning and execution of data collection with the

test subjects. Linda Merrill assisted with data Kreul, E. J., Nixon, J. C., Kryter, K. D., Bell,

analysis. Paul Smith provided many good D.W., Lang, S. W., and Schubert, E. D.

suggestions. Paul Weathersby and Michael (1968). A proposed test of speech disCurley provided useful editorial comments on in a r nal of SecanHar

an earlier version of this paper.

References Ludvigsen, C. (1985). Relations among

some psychoacoustic parameters in norNational Standards Institute. (19). mal and cochlearly impaired listeners.

American national standard Journal of the Acoustical Society of AmerDraft of the American national standard

methods for the calculation of the Speech ica, 78, 1271-1280.

Intelligibility Index; Ver 3.0. NY: Author. Navy Environmental Health Center. (1990).

Benter, R. and Pavlovic, C. V. (1989). Trans- An evaluation of Navy enlisted ratings susfer functions and correction fctors used pected to be at greatest risk for noise

fer an uncion corecton actrs sedinduced hearing loss (Navy Environin hearing aid evaluation and research. mental health C Nter Enirort

Ear nd 1, Harig, 5863.mental Health Center Technical Report Ear and Hearing, 10, 58-63.NHCR9-) NEHC-TR91-1).

Chief of Naval Operations. (1979). 1: Shio- Pavlovic, C. V. (1987). Derivation of priboard Habitability Program (OPNAV- mary parameters and procedures for use in

INST 9640). Washington, DC: DON. speech intelligibility predictions. Journal

Dubno, J. R., He, N., Schaefer, A., and Ahl- of the Acoustical Society ofAmerica, 82,

Dubno,413-422.

strom, J. B. (1992). Predicting consonant

recognition in low-pass maskers from Pavlovic, C. V., Rossi, M., and Espesser, R.

masked thresholds. (Abstracts of the Fif- (1990). Statistical distribution of speech

teenth Midwinter Research Meeting of the for various languages. 120th Meeting of

Association for Research in Otolaryngol- the Acoustical Society of America, San Diogy, p. 65.) ego, California. (Abstract: Journal of the

French, N. R., and Steinberg, J. C. (1947). Acoustical Society of America, 88, Suppl.

Factors governing the intelligibility of 1, 8SP10).

speech sounds. Journal of the Acoustical Sylvester, R. J. (1993). Characterizing noise

Society ofAmerica, 19, 90-119. fields in shipboard spaces (NSMRL ReHumes, L E., Espenoza-Veras, B., and Watson, port Number 1185). Groton, CT: Naval

C. S. (1988). Modeling sensorineural Submarine Medical Research Laboratory.

8
Note: Tables A-i through A-4 are Sl~s at several

background noise levels. These S]Is are plotted

in the text as Figures I and".
Table A-I

Slls for four speech levels (from normal to shout) with a pink-noise background of 60

dBA and tones (sequentially presented tones in random order at 720, 800, 880, 960,

1040, and 1120 Mz) at 77, 83, and 89 dB SPL. The listener has normal hearing.

MASKER

SPEECH LEVEL PINK 60 PINK 60+ TONE 77 PINK 60+ TONE 83 PINK 60+ TONE 89

NORMAL 0.387 0.255 0.222 0.189

RAISED 0.630 0.450 0.393 0.324

LOUD 0.829 0.657 0.573 0.479

SHOUT 0.883 0.802 0.740 0.637

Table A-2

SIIs as in Table I except with a pink-noise background of 65 dBA.

MASKER

SPEECH LEVEL PINK 65 PINK 65+ TONE 77 PINK 65+ TONE 83 PINK 65+ TONE 89

NORMAL 0.291 0.188 0.170 0.156

RAISED 0.485 0.379 0.356 0.321

LOUD 0.735 0.632 0.584 0.527

SHOUT 0.922 0.860 0.817 0.754

Table A-3

Slis as in Table I except with a pink-noise background of 70 dBA.

MASKER

SPEECH LEVEL PINK 65 PINK 65+ TONE 77 PINK 65+ TONE 83 PINK 65+ TONE 89

NORMAL 0.114 0.081 0.080 0.080

RAISED 0.305 0.217 0.189 0.157

LOUD 0.524 0.429 0.373 0.314

SHOUT 0.740 0.652 0.596 0.514

Appendix A-2
Table A-4

Slls as in Table I except with a hearing loss allowable for an officer in the U.S. Navy.

MASKER

SPEECH LEVEL PINK 60 PINK 60+ TONE 77 PINK 60+ TONE 83 PINK 60+ TONE 89

NORMAL 0.371 0.239 0.206 0.176

RAISED 0.576 0.396 0.338 0.272

LOUD 0.739 0.567 0.483 0-392

SHOUT 0.767 0.685 0.624 0.524

Table A-5

SAeech-to-noise ratios (SNRs) modeled (SI1) with a normal vocal effort, pink noise at 60

dBA, and tones at 89 dB SPL. The "noise" was either the pink noise or the hearing

threshold, whichever was greater. The hearing loss was thresholds of 20, 30, 35, 40, 55,

90, and 90 dB SPL at 500, 1000, 2,000, 3,000, 4,000, 6,000, and 8,000 Hz, respectively.

SNRs lower than -14 dB do not contribute to the SI1.

1/3-Octave 1/3- Octave SNR for

Band Band Center 0 dB HL SNR for Band

Number Frequency (Hz) thresholds hearing loss Importance

1 160 -0.2 -0.2 0.0083

2 200 2.8 2.8 0.0095

3 250 4.1 4.1 0.0150

4 315 4.3 4.3 0.0289

5 400 5.9 5.9 0.0440

6 500 6.6 6.6 0.0578

7 630 5.4 5.4 0.0653

8 800 -38.1 -38.1 0.0711

9 1000 -40.4 -40.4 0.0818

10 1250 -0.7 -0.7 0.0844

11 1600 -2.5 -2.5 0.0882

12 2000 -4.3 -4.3 0.0898

13 2500 -6.9 -6.9 0.0868

14 3150 -8.1 -8.1 0.0844

15 4000 -9.3 -24.2 0.0771

16 5000 -12.3 -46.5 0.0527

17 6300 -14.1 -64.1 0.0364

18 8000 -14.5 -64.5 0.0185

Appendix A-3
A i

Appendix A-4
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REPORT DOCUMENTATION PAGE OMF No. 07",,-1,

ig. REPORT SECURITY CLASSIFICATION I b RESTRICTIVE MARKINGS

2a. SECURfIY CLASSIFICATION AUTHORITY 3. DISTRUfJO0AVALABrf1Y OF THE REPORT

A__ro.ed for p tb1i release;

2b. DECLASSIFICATION/DOWNGRADING SCHEDULE aistribution Elimite

4. PERFORMING ORGANIZATION REPORT NUMBERS) 5. MONITORING ORGANIZATION REPORT NUMBER(S)

NSMRL Report 1188 NA

6L NAME OF PERFORMING ORGANIZATION 6b. OFFICE SYMBOL 7a. NAME OF MONITORING ORGANIZATION

Naval Submarine Medical (I ' IMII) NavalMedical Research and Development Research Laboratory C;;and

Sc. ADDRESS (City, Sate, Zip Code) lb. ADDRESS (City, Sate, Zp Code)

Box 900, Naval Suhmarine Base NLON, 1891 Wigoonsin Ave., Bethesda, MD

Groton, CT 06349-5900 9-506

8a. NAME OF FUNDING/SPONSORING 8b. OFFICE SYMBOL 9. PROCUREMENT INSTRUMENT IDENTIFICATION NUMBER

ORGANIZATION (if A~plkabte)

Naval Sea Systems Command I

Sc. ADDRESS (City, Skite, Zip Code) 10. SOURCE OF RJNDING NUMBERS

2531 National Center, Bldg 3, PROGRAM PROJECTNO. TASK NO. WORKI Washngton, DC 20362-5160 ELEMENT NO. ACCESSION NO. SSAS- 91- 77A01R2 DN242605

11. TITLE (Include Security Classfication)

Evaluation of.cqmmunication during active sonar transmissions with a

speech-recognition model

12. PERSONAL AUTHOR(S)

Lvnne Marshall, Thomas E. Hanna, and Chaslav V. Pavlovic

13@L TYPE OF REPORT 13b. TIME COVERED 14. OF EPOFR (Ye W 15. PAGE COUNT

Interim FROM -_TO 11993 July 30 14

16. SUPPLEMENTARY NOTATION

17. COSATI CODES 18. SUBJECT TERMS (Continue on reverse if necery and idnify by bloc number) FIELD GROUP SUB-GROUP -re. ication; intense tones; FIELD _________ Spechtirc Py speechcci unctn; nese oe; acoustCl ty standards

19. ABSTRACT (Coninue on reverse it neceswry and dsnb yby block nwber)

Predictions using the Speech Intelligibility Index (SI1) are reported for speech recognition in tonal and broadband

noise. Three levels of background pink noise (60, 65, and 70 dBA) were used for the SI1. Tones in the frequency

range around 1000 Hz at 77, 83, and 89 dB SPL were added to the background pink noise. The speech spectra were

for four different vocal efforts (normal, raised, loud, and shouted). The simulated listeners for most of the predictions

were assumed to have normal hearing. A hearing loss was also included for a subset of predictions. If "barely

adequate" speech recognition is used as a criterion, the effects of the background noise can be overcome by

increasing the vocal effort of the speaker, often to a shout.

20. DISTRIBUTION/AVAILABLITY OF ABSTRACT 21. ABSTRACT SECURITY CLASSIFICATION

X UNCLASSIFIED/UNUMITED SAME AS REPORT DTIC USERS Unclassified

22a. NAME OF RESPONSIBLE INDIVIDUAL 22b. TELEPI4ONE (fnt*doeArea Code) 22c. OFFICE SYMBOL

Susan D. Monty, Publications Office (203) 449-3967

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S/N 0102-LF-014-6603 UNICLASSIFIED
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