Speech Intelligibility In Rooms Research Articles

Relationship between Chinese speech intelligibility and speech transmission index using diotic listening

The speech intelligibility in rooms is evaluated using the room impulse responses obtained from the room acoustical simulation software ODEON. The simulated room impulse responses are first convolved with the speech intelligibility test signals recorded in an anechoic chamber, then reproduced through the earphone. The subjective Chinese speech intelligibility scores are obtained and the relationship between Chinese speech intelligibility scores and speech transmission index (STI) is built and validated. The result shows that there is high correlation between Chinese speech intelligibility scores and STI. The STI method can predict and evaluate the speech intelligibility for Mandarin Chinese without changes in the algorithm of the weighting values for diotic listening in rooms.

Sound Absorption Coefficients of Micro-fiber Fabrics by Reverberation Room Method

The sound absorption properties of materials are important not only for noise reduction, but also for controlling reverberation time for speech intelligibility in rooms and for promoting fuller sound in concert halls. Industrial textiles are focusing on these materials' application for sound absorption, thus new textiles were to be examined in relation to this performance. Micro-fiber fabric has fine fibers and a high surface area and it has been used in such applications as wipers, thermal insulator, filters or breathable layers. It can be also used for sound absorption. This paper examines the possibility of using micro-fiber fabrics as sound absorbent materials. We tested the sound absorption coefficients of five micro-fiber fabrics and one regular fiber fabric by the reverberation room method. The results showed that the micro-fiber fabrics' sound absorption is superior to that of conventional fabric with the same thickness or weight, and the micro-fiber fabrics' structure was found to be important for controlling sound absorption according to sound frequency. Fabric density was found to have more effect than fabric thickness or weight on sound absorption, and the Noise Reduction Coefficient increases to its highest value at a fabric density of about 0.14 g/cm3, and it decreases thereafter.

Improving speech intelligibility in reverberant rooms

Speech intelligibility in rooms with long reverberation times has long been a problem for acousticians. This problem is exacerbated when the option for acoustic treatments is not an option for a variety of reasons. In this study, a constant-beamwidth, wide-bandwidth (CBWB) loudspeaker array was used to improve speech intelligibility in two multipurpose rooms where treatment was not an option. A CBWB loudspeaker array was designed with independent beam pattern control on both the horizontal and vertical axes. A wide horizontal beam pattern and narrow vertical pattern were designed to achieve constant coverage from 500 Hz to 4 kHz. The array incorporates four separate arrays, two with nested elements, and linear-phase FIR filters to maintain constant beamwidth over the three octaves of interest. Room simulations were conducted with CATT-Acoustic and the array was implemented and compared to a source with a more conventional coverage pattern. The STI method was used to measure speech intelligibility at several positions throughout the rooms. The study showed an improvement in speech intelligibility and a reduction in measured reverberation times.

The intelligibility advantage of clear speech in noise and reverberation backgrounds: Effects of speaking rate

Clear speech refers to a speaking style that is significantly more intelligible than conversational speech for a variety of listeners and backgrounds, including roomlike backgrounds such as noise and reverberation [Payton et al., J. Acoust. Soc. Am. 95, 1581–1592 (1994)]. Although typically spoken more slowly than conversational speech [e.g., Uchanski et al., J. Speech Hear. Res. 39, 494–509 (1996)], talkers can produce clear speech at normal rates with training [Krause and Braida, J. Acoust. Soc. Am. 112, 2165–2172 (2002)]. Whether this form of clear speech (clear/normal speech) provides similar intelligibility benefits to clear (clear/slow) speech in all situations has not been fully characterized, though some results [Krause and Braida, Iranian Audiol. 2, 39–47 (2003)] suggest that the amount of benefit is more dependent on talker and environment. To investigate this possibility for roomlike degradations, the intelligibility advantage provided by clear/slow and clear/normal speech was evaluated by groups of eight normal-hearing listeners at five signal-to-noise ratios (−4, −2, 0, +2, and +4 dB) and three levels of reverberation (0, 0.18, and 0.6 s). Results for four talkers will be reviewed in order to illustrate the effects of speaking rate and speaking style on speech intelligibility in rooms.

Binaural and spatial factors affecting speech intelligibility in rooms

Prominent complaints of hearing-impaired listeners relate to the difficulties they experience in complex acoustic environments, particularly environments with multiple sources and reverberation. Available data and some theoretical ideas about the nature of the difficulties with speech intelligibility in these environments will be reviewed with impaired listeners in mind. The effects of the spatial characteristics of the sound sources and the room on the binaural signals and their processing is the primary focus of this presentation. Listeners with normal hearing as well as listeners with hearing impairments, with and without hearing aids, will be considered. Theoretical topics to be discussed include the effects of reverberation on interaural differences and on temporal modulation patterns, including the consequences for performance as predicted by standard models of binaural processing. [Work supported by NIH R01 DC00100.]

Prediction of speech intelligibility in rooms—a comparison of five methods

In this paper, five methods for calculating speech intelligibility at listener positions in rooms, from measured impulse responses and speech and noise levels, are presented and compared. All methods involve combining a measure of room reverberation with the received signal-to-noise level differences in the occupied room. The first method involves measured octave-band C50s and signal-to-noise level differences to determine octave-band U50s. The remaining four methods comprise detailed (involving octave-band values) and simplified (involving single- and/or combined-frequency values) versions of two approaches. The first approach (second and third methods) involves measured background-noise levels and values of the Transmission Index measured for infinite signal-to-noise level difference. The second approach (fourth and fifth methods) involves 1000-Hz octave-band early-decay times and A-weighted signal-to-noise level differences. The five methods are briefly presented. Then, predictions by the methods for a number of classrooms are presented and compared, and the differences, the merits, and the disadvantages of the various methods are discussed.

Sound fields and speech intelligibility in rooms

A key objective in the architectural design of buildings is to choose building elements that provide both speech intelligibility within a space, and speech privacy between spaces. Standard measurement and evaluation methods per ASTM standards on speech intelligibility and privacy will be discussed as they relate to field measurements. Field data on the reverberant sound fall-off with distance from the source will be presented for a range of small to mid-sized rooms. The variation in reverberant sound within a space can result in an estimation error for the AI and PI between rooms. A possible approach to resolving this issue will be discussed.

The importance of early reflections for speech intelligibility in rooms

New results demonstrate that in rooms for unamplified speech communication early reflections are important for achieving adequate speech intelligibility and that early reflection energy is typically much greater in magnitude than the direct sound energy. Speech intelligibility was measured using a rhyme test in simulated sound fields that included a direct sound with varied early reflections and reverberant sound along with a constant level of ambient noise. The results confirmed that added early reflection energy is equivalent to increased direct sound energy. The combination of direct sound and early reflections increases the effective signal-to-noise ratio and the related speech intelligibility scores for both impaired and nonimpaired listeners. The new results also show, that for common conditions where the direct sound is reduced, it is only possible to understand speech because of the presence of early reflections. Analyses of measured impulse responses in rooms for speech, in terms of a measure of the benefit from early reflections, show that early reflections can increase the effective signal-to-noise ratio by up to 9 dB. The primary goal of room acoustics design should be to maximize early reflection energy to make possible increased effective signal-to-noise ratios.

Spatial distribution of early reflections and speech intelligibility

The strong early reflections and short delay times have been known to improve the intelligibility of speech heard in rooms. D50 and C80, the most frequently used physical parameters, were developed taking this fact into consideration. However, these monaural parameters have limited applications for the practical design of rooms because of their lack of spatial information. The present work investigates how temporal changes in three-dimensional distribution of early reflections influence speech intelligibility in rooms. A new measurement method, using a five microphone array and an omnidirectional source setup, is employed, and a series of post-processing procedures are involved, for getting different early reflections in their spatial distributions. The changes were made for the impulse responses obtained through a five microphone array in the arrival times of early reflections from all, and the horizontal and vertical directions, respectively. Anechoic samples of the Korean language were convolved binaurally with the reproduced impulses by applying a head-related transfer function. A series of speech intelligibility tests, conducted for 22 university students, found that the percentage of correct responses significantly deteriorated by increasing delay times of early reflections from the vertical direction. The result suggests that vertical components of early reflections play a significant role in improving speech intelligibility. [Work supported by Korean Research Foundation Grant KRF-1999-1-310-004-3.]

Relationship between speech transmission index and easiness of speech perception in reverberatory fields

When evaluating speech intelligibility in rooms, the Tri-syllable articulation test is used as one of the standard indicators in Japan. Sometimes there are differences between auditory impression and the score of the articulation test. So the psychological scale values of easiness of speech perception (ESP) were measured by experiments, which indicated differences between ESP and articulation scores and a good correlation (R=0.9) between ESP and speech transmission index (STI) in reverberation. The purpose of this paper is to point out relationships between the condition of sound field and ESP. The first of two experiments in this study was done in reverberatory fields. Sound-pressure level (SPL) of direct sound, direct sound to first reflection ratio (D/R), initial delay time, frequency characteristics of reverberation, and reverberation time (RT) were varied. The other experiment was done in simulated fields of actual auditoriums. The result of the first experiment shows D/R and RT has alarge effect on ESP and while varying D/R, the correlation between ESP and STI is not good (R=0.6). The second experiment indicates that when the sound source is on the center of the stage, the correlation between STI and ESP is 0.8; and a different tendency is found while using the sound reinforcement system.

Comparisons of measures of speech intelligibility in rooms

The speech transmission index, useful-to-detrimental ratios, and percent articulation losses are three quite different types of measures of speech intelligibility in rooms. They each combine a measure of the speech-to-noise ratio and a room acoustics measure to better relate to speech intelligibility. Variations of all three types of measures were calculated from 91 impulse responses obtained from a wide range of acoustical conditions, and for different speech-to-noise ratios. Several broadband forms of these measures are shown to be reasonably well related to each other. The results are used to derive conversion equations between the three types of measures.

Speech intelligibility in rooms

Speech is a method of communication between two or more minds. The actual forming and understanding of the message are in the physiological domain. The transmission of the speech by sound waves is in the physical domain. Only the latter can be controlled by means of acoustical engineering. The relevant processes in the physiological domain can be contained in the term ‘‘proficiency of speaker and listener.’’ The relevant processes in the physical domain can be contained in the term ‘‘information loss.’’ This paper will deal with: (a) the underlying factors of information loss and assessing them by measurement and calculation as accurately as possible; (b) the means and limitations of quantifying the information loss: ALcons, STI, etc.; (c) for the calculation of the information loss, an adaption of the ‘‘classic’’ Peutz equation, suitable for data generated by contemporary computer programs, will be given; (d) the accuracy of the data, with some examples like comparison of results from word lists, STI measurement and ALcons calculation; (e) results in extreme situations like a large, closed sports stadium with a 9-reverberation time and a tunnel with a length of 1 k; (f) design considerations for sound systems regarding the proficiency of speaker and listener. [See NOISE-CON Proceedings for full paper.]

Evaluation method utilizing subjective MTF measurements for speech perception ability of hearing-impaired listeners

A new method for characterizing the speech perception performance of hearing-impaired listeners in both quiet and noisy environments is proposed. The concept of this method is that one’s spech perception ability depends on the quality of one’s perceived speech sound image. In this method, one’s perceived image quality is related to subjectively a measured modulation transfer function (MTF). The procedure for estimating the sound image quality from measured MTF values obeys that of the RASTI method [Houtgast et al., Acustica46 , 60 (1980)], which is a physical method for predicting speech intelligibility in rooms. The subjective MTFs are obtained from the signal detection experiments using an adaptive 2IFC procedure with a modulated masker noise [Miyata et al., Acustica 73, 200 (1991)]. The proposed method was used to evaluate the monosyllable recognition abilities of six hearing-impaired subjects. The experimental results provide good support to the method for characterizing the speech perception ability of hearing-impaired listeners.

Technical Note: The Influence of Room Shape on Speech Intelligibility in Rooms with Varying Ambient Noise Levels

Technical Note: The Influence of Room Shape on Speech Intelligibility in Rooms with Varying Ambient Noise Levels

Predictors of speech intelligibility in rooms.

Three different types of acoustical measures were compared as predictors of speech intelligibility in rooms of varied size and acoustical conditions. These included signal-to-noise measures, the speech transmission index derived from modulation transfer functions, and useful/detrimental sound ratios obtained from early/late sound ratios, speech, and background levels. The most successful forms of each type of measure were of similar prediction accuracy, but the useful/detrimental ratios based on a 0.08-s early time interval were most accurate. Several physical measures, although based on very different calculation procedures, were quite strongly related to each other.

Speech intelligibility prediction in rooms

Three different types of acoustical measures were compared as predictors of speech intelligibility in rooms of varied size and acoustical conditions. These included signal‐to‐noise type measures, the sound transmission index derived from modulation transfer functions, and useful‐to‐detrimental sound ratios obtained from early‐to‐late sound ratios, speech and background levels. The most successful forms of each type of measure were of similar prediction accuracy, but the useful‐to‐detrimental ratios based on a 0.08‐s early time interval were most accurate. Several physical measures, although based on very different calculation procedures, were found to be quite strongly related to each other.

Predicting speech intelligibility in rooms

The pioneering work of Lochner and Berger [e.g., J. Sound Vib. 1(4), 426–454 (1964)] has provided a basis for measuring and calculating speech intelligibility in rooms in terms of a ratio of useful early sound to detrimental late arriving sound and background noise. In the present work their results are used in an image sources computer model to predict speech intelligibility in rooms. The calculation procedure is discussed and the influence on speech intelligibility of room geometry, room surface sound absorption properties, and background noise levels are investigated. Comparisons are made with speech intelligibility calculations based on the modulation transfer function approach.

Speech intelligibility in rooms

This paper reviews developments in the science of speech intelligibility in rooms, and discusses the need for further work. Over the last 60 years, knowledge on this subject area of auditorium acoustics has been ascertained by observation and experiment, critically tested, systematized, and brought under a set of general principles. Objective indices are now available for measuring and predicting speech intelligibility in rooms without the need for traditional subjective testing procedures. Thus a more widespread application of intelligibility criteria in auditorium design is to be expected in future work. Parallel with the developments in objective and subjective measurement techniques, the computer prediction of reflection patterns in rooms has been developed so that speech intelligibility levels can now be ascertained during design, and acoustic faults remedied before construction commences. However, further work is needed to establish a valid basis for speech intelligibility design criteria based on objective measurements. To this end, a catalog of subjective and objective measures of speech intelligibility could be determined for a set of conditions in well‐known auditoria. The result would be a relative scale of intelligibility values for use by practitioners. [Work supported by the SERC, United Kingdom.]

Predicting and measuring speech intelligibility in rooms

A well‐known concept—the Modulation Transfer Function MTF—which has only recently been adapted to the field of room acoustics, can successfully be used for predicting or measuring speech intelligibility in rooms. The MTF in room acoustics characterizes the quality of sound transmission between two points in a room by specifying the reduction of the original fluctuations in the signal (more specifically, the reduction of the modulation depth as a function of modulation frequency), brought about by interfering noise and/or reverberation. The relevance of this approach for speech intelligibility has been verified by a large‐scale international test: it was found that the results of the MTF analysis (in which an MTF is converted into a single index, the Speech Transmission Index STI) relate well with the mean results of various intelligibility tests for different languages. The accessibility of the MTF approach for architects and acousticians has been substantiated by (1) the development of a calculation sche...

Room acoustics for the aged.

This article deals with the combined effects of noise and reverberation on the speech-reception threshold for sentences. It is based on a series of current investigations on: (1) the modulation-transfer function as a measure of speech intelligibility in rooms, (2) the applicability of this concept to hearing-impaired persons, and (3) hearing loss for speech in quiet and in noise as a function of age. It is shown that, generally, in auditoria, classrooms, etc. the reverberation time T, acceptable for normal-hearing listeners, has to be reduced to (0.75)DT in order to be acceptable for elderly subjects with a hearing loss of D dB for speech in noise; for listening conditions as in lounges, restaurants, etc. the corresponding value is (0.82)DT.