Evaluation of Auditory Characteristics of Communications 

and Hearing Protection Systems (C&HPSs) 

Part II – Speech Intelligibility 

by Paula Henry and Rachel Weatherless 

ARL-TR-5075 January 2010 

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Army Research Laboratory 

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ARL-TR-5075 January 2010 

Evaluation of Auditory Characteristics of Communications 

and Hearing Protection Systems (C&HPSs) 

Part II – Speech Intelligibility 

Paula Henry and Rachel Weatherless 

Human Research and Engineering Directorate, ARL 

Approved for public release; distribution is unlimited. 
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Evaluation of Auditory Characteristics of Communications and Hearing Protection 

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14. ABSTRACT 

Devices that provide hearing protection, situational awareness, and radio communications are often referred to as 

Communications and Hearing Protection Systems (C&HPSs). Soldiers use these systems while deployed to navigate within 

their environment, communicate with their team members, and protect their hearing. Each of the three features of select 

C&HPSs (hearing protection, speech communication, and situational awareness) was evaluated by the U.S. Army Research 

Laboratory in order to obtain data that is independent from that provided by the manufacturer. This report is the second in a 

series of three and focuses on the speech intelligibility performance obtained from two commercially available C&HPSs: 

Nacre QuietPro and Silynx QuietOps selected from three C&HPSs evaluated for attenuation characteristics in the first report. 

Results of the speech intelligibility testing indicated that the Silynx QuietOps provides a significantly higher degree of speech 

intelligibility, but this difference is probably not significant for field applications. The differences noted in speech intelligibility 

are likely due to a combination of differences in the frequency responses measured from the two systems and differences in the 

frequency responses of the microphones from the two systems, along with small differences in the output intensity of the 

speech items provided to the listeners. 

15. SUBJECT TERMS

hearing, communication, C&HPS, situational awareness, speech intelligibility 

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Paula Henry 

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iii

Contents 

List of Figures iv

List of Tables iv

Acknowledgments v

1. Introduction 1

1.1 Nacre AS – QuietPro .......................................................................................................2

1.2 Silynx Communications, Inc. – QuietOps .......................................................................3

2. Methods 3

2.1 Participants ......................................................................................................................3

2.2 Procedures .......................................................................................................................4

3. Results 5

4. Discussion 6

5. Conclusions 8

6. References 9 

Distribution List 11 
iv

List of Figures 

Figure 1. Photo of the Nacre QuietPro system (downloaded from: 

armorcorpus.com/products.html, 28 August 2009). ..................................................................2

Figure 2. Photo of the Silynx QuietOps system (downloaded from: 

http://www.janes.com/events /exhibitions/dsei2007/sections/daily/day1/allinone-tacticalheadset.shtml, 28 August 2009). ................................................................................................3

Figure 3. Average MRT scores for the 12 participants for the two communications and 

hearing protection systems. Error bars indicate +1 standard deviation. ...................................5

Figure 4. Frequency responses in 1/3 octave bands measured from the earphones of the two 

systems. The responses are equalized for the value at 1000 Hz. Frequency is shown on 

the x-axis and intensity is shown on the y-axis..........................................................................7

List of Tables 

Table 1. Average real-ear attenuation at threshold values and standard deviations for the 12 

participants for the two communications and hearing-protection systems from Henry and 

Weatherless (2010). ...................................................................................................................8
v

Acknowledgments 

The authors wish to thank the individuals who voluntarily participated in the study. The authors 

also thank the three technical reviewers (Frank Morelli, Jeremy Gaston, and Timothy Mermagen) 

for providing helpful comments and suggestions for improving this report. Special thanks go to 

Timothy Mermagen who created the software for the Modified Rhyme Test and served as the 

speaker in the recordings and to Ashley Foots for assistance in editing the recordings to create 

stimulus sound files. 
vi

INTENTIONALLY LEFT BLANK. 
1

1. Introduction

Dismounted Soldiers need to hear what is happening within their immediate surroundings (have 

situational awareness), communicate with other Soldiers over radios, and be protected from 

hazardous continuous and impulse noise (hearing protection). These three hearing abilities are 

essential for dismounted Soldiers and can be seen as conflicting goals for development of such 

multipurpose communication devices. Balance must be maintained between hearing protection 

and auditory situational awareness, which is often the biggest challenge for a developer. 

Hearing-protection devices that cover or plug the ears (like earmuffs or earplugs) will provide 

hearing protection and good radio communication, but they are likely to reduce the situational 

awareness for the individual Soldier. Leaving the ears open allows for good situational 

awareness but not protection against hazardous noise. Providing all three aspects within a single 

device can be very challenging. 

There are several devices available which provide hearing protection yet still allow for adequate 

situational awareness and radio communications. These devices are often referred to as 

Communications and Hearing Protection Systems (C&HPSs). The U.S. Army needs information 

on how these systems function in a militarily-relevant environment in order to determine devices 

which should be provided to Soldiers as well as determine appropriate areas for research to 

improve the effectiveness of these devices. 

In the evaluation of C&HPS, the three auditory aspects need to be evaluated: attenuation 

provided for hearing protection, speech intelligibility of radio communication, and auditory 

localization as a measure of situational awareness. Sound attenuation can be provided to the user 

through passive or active means. Passive attenuation is provided by the mere presence of the 

device without any processing of the sound. Active attenuation cancels or reduces the 

background noise by introducing a signal which is opposite in phase and time to cancel out the 

first sound (Kuo and Morgan, 1999; Oppenheim et al., 1994). Active noise processes are 

referred to as active noise cancellation (ANC) or active noise reduction (ANR). A popular 

implementation of ANR is in the headphones marketed to frequent fliers for listening to music 

on airplanes. ANR reduces low frequency noise better than high frequency noise. 

The goal of the first part of the three-part study was to measure the passive sound attenuation 

provided by three in-the-ear C&HPSs using Method A (experimenter fit) of the Real-ear 

Attenuation at Threshold (REAT) procedure (ANSI, 2002). The values obtained were intended 

to demonstrate best-case scenario attenuation from the products but will be overestimates of realworld performance of these devices (Berger, 1986; Franks et al., 2000; Royster et al., 1996). 

Three C&HPSs were evaluated in that portion: the Nacre QuietPro,*

 the Silynx QuietOps,† and 

 *

 QuietPro is a registered trademark of Nacre AS, Norway. 

†

 QuietOps is a trademark of Silynx Corporation, Rockville, MD. 
2

the Sennheiser SLC-110 (Henry and Weatherless, 2010). The Sennheiser SLC-110 was found to 

provide very low levels of attenuation and concerns were raised that for at least some 

participants, the system may not provide adequate hearing protection in the presence of the 

planned level of background noise of 95 dB A. Therefore, the Sennheiser SLC-110 was dropped 

from this portion of the study. The goal of this second part of the three-part study was to 

measure the speech intelligibility across radio communications of two select in-the-ear C&HPSs 

(ANSI, 1999). 

Two C&HPSs were used for the speech intelligibility testing: the Nacre QuietPro and the Silynx 

QuietOps. Descriptions of the two systems follow. 

1.1 Nacre AS – QuietPro 

The Nacre QuietPro is an in-the-ear digital hearing protector and communication headset 

designed for use with military tactical radios and intercom systems. A picture of the device is 

shown in figure 1. Nacre AS is a company based in Norway. The QuietPro system uses a digital 

signal processor to facilitate automatic, adaptive digital hearing protection through ANR in 

addition to its passive attenuation. According to the manufacturer, the QuietPro helps protect the 

user’s hearing by attenuating ambient noises and canceling excessive acoustic peaks and 

impulses, resulting from nearby running engines, explosions, and gun shots. Using both passive 

and active means, Nacre states that QuietPro can achieve 34–42-dB attenuation, but there is no 

indication regarding the attenuation provided to low intensity sounds vs. that provided to impulse 

noise. The device is fit in the ear with disposable Comply* canal tips that are specifically designed 

for use with the QuietPro system. The Comply tips are available in three sizes: small, medium, and 

large. Information for the system can be obtained from: http://www.nacre.no. 

Figure 1. Photo of the Nacre QuietPro 

system (downloaded from: 

armorcorpus.com/products.html, 

28 August 2009).

 *

Comply is a trademark of Hearing Components, Oakdale, MN. 
3

1.2 Silynx Communications, Inc. – QuietOps 

The Silynx QuietOps is an in-the-ear tactical communication headset designed for use by 

dismounted Soldiers. A picture of the device is shown in figure 2. Silynx is a Delaware 

Corporation whose principal location is in Rockville, MD. The QuietOps allows users to 

monitor one or two communications devices simultaneously—two radios or a radio and an 

intercom. The device allows the user to determine which communication channel has priority 

over the other or the user can program the device to have each communication device going to a 

different ear. The QuietOps is fit to the listener’s ear with a compressible foam plug that sits on 

the end of the device. The foam plugs are disposable and come in three sizes: small, medium 

and large. No information is provided from the company regarding attenuation. Information for 

the system can be obtained from: http://www.silynxcom.com/. 

Figure 2. Photo of the Silynx QuietOps system (downloaded from: http://www.janes.com/events 

/exhibitions/dsei2007/sections/daily/day1/allinone-tactical-headset.shtml, 28 August 2009). 

2. Methods 

2.1 Participants 

Twelve male volunteers between the ages of 19 and 23 (M = 20) participated in the study. None 

of the participants had extensive prior experience with the C&HPSs used in the study. All 

participants had normal hearing sensitivity defined as pure-tone hearing thresholds of ≤25-dB 

hearing level (HL) at audiometric frequencies from 125 through 8000 Hz (ANSI, 2004). All 

participants had American English as their native language. All data were collected in 

compliance with regulations from the Institutional Review Board at the U.S. Army Research 

Laboratory. Informed consent was obtained from participants prior to their participation in the 

research study.
4

2.2 Procedures 

Speech intelligibility was measured as the percentage of words understood in the presence of 

background noise. Items from the Modified Rhyme Test (MRT) were recorded by a male talker 

in the presence of background noise through the two C&HPSs simultaneously. These recordings 

were edited to isolate the individual items. The carrier phrase used for the recordings was “Mark 

the _______ now” in which the MRT item was inserted into the blank within the phrase. The 

outputs of the microphones for the C&HPSs were routed through the sound card of a Dell laptop 

computer. The recordings were then edited using Sound Forge* software and played back to the 

listeners through the same Dell personal computer routed through a Symetrix†

 SX204 headphone 

amplifier to the earphones of the C&HPS headsets. In this way, the C&HPSs were constant 

components of the test paradigm without the need to have a live talker. 

Background noise consisted of a looped 7-min recording of the inside of an M113 traveling on a 

gravel road at a rate of 10 mph. The intensity level of the background noise was limited to 

95 dB A to ensure safe exposure levels based on the attenuation measured made with the 

C&HPSs in the first part of this series (Henry and Weatherless, 2010). All data collection took 

place in the acoustically treated areas of Building 520 at Aberdeen Proving Ground, MD. Four 

Infinity‡ Studio Monitor 150 loudspeakers were positioned in the room to output the background 

noise during the test trials. The loudspeakers were ~1 m from the position of the listener and 

were directed toward the listener’s chair. The background noise was output to the loudspeakers 

from a Dell personal computer through a Crown§ D-75 amplifier. 

Participants were fitted with each C&HPS according to the manufacturer’s guidelines. The 

intensity level of the systems was equated between the two systems through perceptual 

comparisons. Participants were not able to adjust the volume. 

Test material consisted of the MRT, which consists of 50 six-word groups of monosyllabic 

English words (House et al., 1965). There are therefore 300 words in the MRT. The words in 

each group have very similar sounds and they differ by either initial or final phoneme. Almost 

all the test items are consonant-vowel-consonant words. 

Participants listened to all 300 items of the MRT test played through each of the C&HPSs one at 

a time and selected which word from the given six words was the correct one. Participants 

interfaced with the computer through a keyboard and/or mouse and a custom written computer 

software program. Participants completed the procedure with both devices in a single session. 

The ordering of the devices was counterbalanced across the participants.

 *

Sound Forge is a registered trademark of Sony Creative Software, Inc., Madison, WI. 

†

Symetrix is a trademark of Symetrix, Inc., Mountlake Terrace, WA. 

‡

Infinity is a trademark of Harman International Industries, Inc., Stamford, CT. 

§

Crown is a registered trademark of Crown International, a Harman International Company, Stamford, CT. 
5

The individual data points were the listeners’ performance on the speech intelligibility task for 

the transmitted words for each C&HPS. Two transformations were made to the scores prior to 

data analysis: transformation to rationalized arcsine units (rau) and correction for chance. The 

transformation to rau was to convert percent correct data into interval data which are appropriate 

for statistical analysis (Sherbecoe and Studebaker, 2004; Studebaker, 1985). Following 

conversion to rau, all individual scores were adjusted for the probability of getting a correct 

response by chance through use of a closed-set task (ANSI, 1999). The conversion to raus and 

correction for guessing was based on the following formula: 

T  (A*T 100)/(A 1) C U , (1) 

where Tc is the adjusted score, Tu is the uncorrected score, and A is the number of alternative 

choices per item (6) (Sherbecoe and Studebaker, 2004). 

3. Results 

Figure 3 shows the average percent correct scores obtained on the MRT for the two C&HPSs 

used in the current study. Although analyses were conducted on rau values, results are presented 

as average percent correct. 

Figure 3. Average MRT scores for the 12 participants for the two communications 

and hearing protection systems. Error bars indicate +1 standard deviation. 
6

As seen in figure 3, use of the Silynx QuietOps resulted in higher speech intelligibility scores 

than use of the Nacre QuietPro. The average speech intelligibility scores were 85.46% and 

80.79% for the Silynx QuietOps and Nacre QuietPro, respectively. The variability of speech 

intelligibility across participants was roughly the same between the two devices. 

A paired-samples t-test on the transformed and corrected speech intelligibility scores indicated a 

significant difference between the two systems, t(11)=3.384, p<.01, with the Silynx QuietOps 

outperforming the Nacre QuietPro. 

4. Discussion 

Note that although the statistical analysis revealed a significant difference between the 

performances with the two C&HPSs, the actual speech intelligibility difference was very small 

(5%) and is within expected variability of such speech tests. Furthermore, this small difference 

would not likely be meaningful in a real-world scenario. The testing conducted in this study 

involved the speech intelligibility of individual words embedded in a carrier phrase. The 

contextual advantage of phrases and sentences typically allows for higher speech intelligibility 

than with individual words. Therefore, a 5% difference in intelligibility of individual words is 

not likely to impact operational performance with connected speech. 

There are three possible reasons for the difference in speech intelligibility performance: 

differences in the presentation signal-to-noise ratio (SNR) due to differences in the frequency 

responses of the two systems, differences in intensity level of the stimuli provided to the 

listeners, differences in attenuation between the two systems and differences in microphone 

characteristics of the two systems. 

Differences in SNR are well known to cause differences in speech intelligibility (French and 

Steinberg, 1947; Hawkins and Stevens, 1950; Plomp, 1978). To investigate differences in the 

SNR available to the listener, frequency responses of the earphones of each system were 

measured through a Knowles Electronics Manikin for Acoustic Research (KEMAR). The 

earpieces of each system were placed into the ears of the KEMAR. A white noise, created 

through Sound Forge software, was sent out of a laptop computer and through the system in the 

same way that the speech recordings were provided to the listeners. The outputs from each 

device were recorded onto a laptop computer through 01dB* software. Fast Fourier transform 

(FFT) analysis was conducted on a 5-s recording of the white noise and analyzed in 1/3 octave 

bands. Figure 4 shows the responses from the two systems equalized for the value at 1000 Hz. 

 *

01dB is a trademark of 01dB-Metravib SA, France. 
7

Figure 4. Frequency responses in 1/3 octave bands measured from the earphones 

of the two systems. The responses are equalized for the value at 

1000 Hz. Frequency is shown on the x-axis and intensity is shown on 

the y-axis. 

As shown in figure 4, the Silynx QuietOps system has a flatter response in the low and mid 

frequencies and a peak around 2500 Hz. The Nacre QuietPro system has a multi-peaked 

response with peaks at 1300–1600, 4000, and 6300 Hz. It is possible that the differences in the 

peak energy provided to the listener resulted in the differences in speech intelligibility. 

Second, there is a possibility that there were small differences in the intensity level of the stimuli 

provided to the listeners. Note that the output levels of the two systems were equated for 

perceptual loudness by the two investigators and that the volume control could not be adjusted 

by the listener. It is possible that the output of the Silynx QuietOps system was slightly higher 

than the Nacre QuietPro system leading to a more favorable SNR for the listener when listening 

through the Silynx QuietOps system. However, given that two listeners agreed on the perceptual 

loudness of the stimuli, large differences are not anticipated. 

It is also possible that the microphones of the two systems differ in their frequency response 

characteristics that altered the frequency content of the stimuli provided to the listener resulting 

in additional SNR advantages for the QuietOps. 

Lastly, the attenuation provided by the two systems was compared. Data in table 1 were 

obtained from Henry and Weatherless (2010) which demonstrated that the Nacre QuietPro 

provided a greater level of attenuation than the Silynx QuietOps. This is the opposite pattern 

than would be expected if attenuation was a contributing factor to the differences in speech 

intelligibility seen with the two systems. 
8

Table 1. Average real-ear attenuation at threshold values and standard deviations for the 12 participants for the 

two communications and hearing-protection systems from Henry and Weatherless (2010). 

Frequency 

(Hz) 

System 125 250 500 1000 2000 4000 8000 

Silynx 

QuietOps 17.5 ± 8.6 17.3 ± 8.4 15.4 ± 9 17.1 ± 9.4 23.8 ± 7.6 27.3 ± 9.8 34.1 ± 13 

Nacre 

QuietPro 23.3 ± 8.4 24.6 ± 9.4 25.4 ± 10.7 26.3 ± 8.5 29.2 ± 6.1 31.9 ± 5.2 37.1 ± 6.5 

It is worth noting that although only small differences were demonstrated in speech intelligibility 

for the two devices, all of the participants in the study indicated a strong preference for the sound 

provided by the Silynx QuietOps system. This preference is most likely due to the improved 

speech intelligibility provided by this device. This difference in sound quality can be attributed 

to a combination of differences in frequency responses of the earphones and potentially of the 

microphones along with possible differences in the output intensity levels provided by the two 

systems. 

5. Conclusions 

This is the second in a series of three reports on the evaluation of communication and hearing 

protection systems. The first study focused on the attenuation provided by each of the systems to 

low intensity sounds. The present study focused on the speech intelligibility provided by the 

output of the C&HPSs to the listeners. Across the two systems evaluated, the Silynx QuietOps 

was shown to result in better speech intelligibility; however, the difference was small and may 

not be meaningful in field applications. This difference is likely due to a combination of factors 

including differences in frequency responses of the earphones and microphones along with small 

differences in the intensity levels of the stimuli provided to the listeners. 
9

6. References 

American National Standards Institute (ANSI). Method for Measuring the Intelligibility of 

Speech Over Communication Systems; ANSI S3.2-1989; Washington, DC, 1999. 

American National Standards Institute. Methods for Measuring the Real-Ear Attenuation of 

Hearing Protectors; ANSI S12.6-1997; Washington, DC, 2002. 

American National Standards Institute. Specification for Audiometers; ANSI S3; Washington, 

DC, 2004. 

Berger, E. H. Methods of Measuring the Attenuation of Hearing Protection Devices. Journal of 

the Acoustical Society of America 1986, 79 (6), 1655–1687. 

Franks, J.; Murphy, W.; Johnson, J.; Harris, D. Four Earplugs in Search of a Rating System. 

Ear and Hearing 2000, 21 (3), 218–225. 

French, N.; Steinberg, J. Factors Governing the Intelligibility of Speech Sounds. Journal of the 

Acoustical Society of America 1947, 19, 90–119. 

Hawkins, J.; Stevens, S. The Masking of Pure Tones and of Speech by White Noise. Journal of 

the Acoustical Society of America 1950, 22 (1), 6–13. 

Henry, P.; Weatherless, R. Evaluation of Auditory Characteristics of Communications and 

Hearing Protection Systems (C&HPSs) Part I – Sound Attenuation; ARL-TR-5050. U.S. 

Army Research Laboratory: Aberdeen Proving Ground, MD, January 2010. 

House, A. S.; Williams, C. E.; Heker, M. H.; Kryter, K. D. Articulation Testing Methods: 

Consonantal Differentiation with a Closed-Response Set. Journal of the Acoustical Society 

of America 1965, 37, 158–166. 

Kuo, S.; Morgan, D. Active Noise Control: A Tutorial Review. Proceedings of the IEEE, 1999; 

Vol. 87, No. 6, pp 943–973. 

Oppenheim, A.; Weinstein, E.; Zangi, K.; Feder, M.; Gauger, D. Single-Sensor Active Noise 

Cancellation. IEEE Transactions on Speech and Audio Processing 1994, 2 (2), 285–290. 

Plomp, R. Auditory Handicap of Hearing Impairment and the Limited Benefit of Hearing Aids. 

Journal of the Acoustical Society of America 1978, 63 (2), 533–549. 

Royster, J.; Berger, E.; Merry, C.; Nixon, C.; Franks, J.; Behar, A.; Casali, J.; Dixon-Ernst, C.; 

Kieper, R.; Mozo, B.; Ohlin, D.; Royster, L. Development of a New Standard Laboratory 

Protocol for Estimating the Field Attenuation of Hearing Protection Devices. Part I. 

Research of Working Group 11, Accredited Standards Committee S12, Noise. Journal of 

the Acoustical Society of America 1996, 99 (3), 1506–1526.
10

Sherbecoe, R.; Studebaker, G. Supplementary Formulas and Tables for Calculating and 

Interconverting Speech Recognition Scores in Transformed Arcsine Units. International 

Journal of Audiology 2004, 43, 442–448. 

Studebaker, G. A Rationalized Arcsine Transform. Journal of Speech and Hearing Research

1985, 28, 455–462. 
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 1 ARMY RSCH LABORATORY – HRED 

 RDRL HRM DW E REDDEN 

 BLDG 4 CL 60 

 FORT BENNING GA 31905-5400 

 1 ARMY RSCH LABORATORY – HRED 

 RDRL HRM CN R SPENCER 

 DCSFDI HF 

 HQ USASOC BLDG E2929 

 FORT BRAGG NC 28310-5000 

 1 ARMY G1 

 (CD DAPE MR B KNAPP 

 only) 300 ARMY PENTAGON RM 2C489 

 WASHINGTON DC 20310-0300 

 1 ARMY RSCH LABORATORY – HRED 

 RDRL HRM D T DAVIS 

 BLDG 5400 RM C242 

 REDSTONE ARSENAL AL 35898-7290 

ABERDEEN PROVING GROUND

 5 DIR USARL 

 RDRL CIM G 

 S FOPPIANO 

 RDRL HR 

 T LETOWSKI 

 RDRL HRM B 

 J LOCKETT 

 RDRL HRS 

 L ALLENDER 

 RDRL HRS D 

 B AMREIN 
NO. OF NO. OF 

COPIES ORGANIZATION COPIES ORGANIZATION

14

 2 SILYNX COMMCTNS INC 

 P WALTON 

 G LIMONCHIK 

 9901 BELWARD CAMPUS DR 

 STE 150 

 ROCKVILLE MD 20850 

 1 SENNHEISER ELECTRONIC CORP 

 D DUNLAP 

 1 ENTERPRISE DR 

 OLD LYME CT 06371 

 1 NACRE US INC 

 B J BURNS 

 104 BUD PL 

 ABERDEEN NC 28315 

 1 ARNOLD ENGRNG DEV CTR 

 AEDC 716 TS 

 V S BJORN 

 740 FOURTH ST 

 ARNOLD AFB TN 37389-6000 

 1 DIRECTOR 

 AIR FORCE RESEARCH LAB 

 PRINCIPAL ACOUSTICS SCIENTIST 

 R MCKINLEY 

 WPAFB OH 45431 

 2 USAARL 

 E REEVES 

 M HILL 

 6901 ANDREWS AVE 

 PO BOX 620577 

 FORT RUCKER AL 36362-0577 

 1 NVL SUBMARINE MED RSRCH LAB 

 L MARSHALL 

 BOX 900 SUBASE NLON 

 GROTON CT 06349-5900 

 1 PROPONENCY OFC FOR PREVENTIVE 

 MED 

 DASG PM 

 V TUTEN 

 5111 LEESBURG PIKE STE 538 

 FALLS CHURCH VA 22041 

ABERDEEN PROVING GROUND

 1 COMMANDER 

 US ARMY CTR FOR HEALTH 

 PROMOTION & PREVENTIVE 

 MEDICINE 

 PROJ MGR ARMY HEARING PRGM 

 MCHB TS MHC 

 E FALLON 

 5158 BLACKHAWK RD 

 BLDG E4435 

 APG MD 21010-5403 

 25 DIR USARL 

 RDRL HRS D 

 P HENRY (20 CPS) 

 R WEATHERLESS (5 CPS)