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Correlational Analysis of Speech Intelligibility Tests and Metrics for Speech Transmission

Analysis of the common methods of evaluating the quality and limitations of speech could serve as a resource for users of standard speech intelligibility measurement methods.

Speech is a form of language (communication code) that uses vocally produced sounds to convey thoughts, meanings, and feelings. To communicate by speech, speech sounds must be both produced and perceived. Speech production refers to the process by which predetermined vocalized sounds are produced by the talker and organized in sequences forming communication signals. Speech perception is the process by which the listener is able to hear and interpret (understand) the message encoded in the speech signals.

The effective design and use of audio communication systems requires some knowledge of the physical properties of speech and the rules that govern the human perception of speech. The two main physical descriptors of speech signal are its sound intensity and spectral content.

The long-term average sound intensity levels of phonated speech produced with various levels of vocal effort are as follows:

However, individual phonemic components of speech vary greatly in their intensity with vowels carrying much greater energy than consonants. The strongest vowel, /aw/, as in the word “all,” is about 28 dB more intense than the weakest consonant, /th/, as in the word “thin.” Whispered (unphonated) speech levels are in the order of 40 dB(A), but this kind of speech is not used in formal communication.

A person’s vocal level effort depends on the visual and auditory clues stemming from the distance (real or perceived) to the listener and the emotional state of the talker. In noisy environments vocal effort is naturally higher (raised, loud, or shouted) than in quiet (normal) environments, because talkers involuntarily raise their voices to the level needed for them to hear themselves. Conversely, talkers wearing hearing protectors reduce their vocal efforts by about 3 dB, compared to when unprotected, if the background noise level exceeds 75 dB A (ISO 2003).

The speech levels referenced above are the levels measured in front of the talker’s mouth. However, the vocal source is quite directional and the levels at the talker’s back may measure up to 5–7 dB lower. This difference is relatively small at low- and mid-frequencies but sharply increases for spectral content at higher frequencies (consonants).

This work was done by Tomasz R. Letowski and Angelique A. Scharine for the Army Research Laboratory. For more information, download the Technical Support Package (free white paper) below. ARL-0229

Topics:
Aerospace Communication systems Data Acquisition Data Acquisition Detectors Hardware Input Devices Sensors Software Telecommunications Test & Measurement
This Brief includes a Technical Support Package (TSP).
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Correlational Analysis of Speech Intelligibility Tests and Metrics for Speech Transmission

(reference ARL-0229) is currently available for download from the TSP library.

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    Aerospace & Defense Technology Magazine

    This article first appeared in the August, 2020 issue of Aerospace & Defense Technology Magazine (Vol. 5 No. 5).

    Read more articles from this issue here.

    Read more articles from the archives here.

    Overview

    The document titled "Correlational Analysis of Speech Intelligibility Tests and Metrics for Speech Transmission" is a technical report authored by Tomasz R. Letowski and Angelique A. Scharine, published by the US Army Research Laboratory in December 2017. The report covers research conducted between June 1, 2017, and September 29, 2017, focusing on the assessment of speech intelligibility, which is crucial for effective communication in various environments, particularly in military settings.

    The primary objective of the study is to analyze the correlation between different speech intelligibility tests and various metrics used to evaluate speech transmission. Speech intelligibility refers to the clarity and comprehensibility of spoken language, which can be affected by numerous factors, including background noise, transmission medium, and speaker characteristics. Understanding these correlations is essential for developing effective communication systems and improving operational effectiveness in environments where clear communication is vital.

    The report outlines the methodologies employed in the research, including the selection of speech intelligibility tests and the metrics used for analysis. It discusses the significance of these tests in evaluating how well speech can be understood in different conditions, which is particularly relevant for military personnel who may operate in noisy or challenging environments.

    The findings of the report are intended to provide insights that can inform the design and implementation of communication systems, ensuring that they are optimized for clarity and intelligibility. The research aims to contribute to the development of standards and guidelines for assessing speech intelligibility in various contexts, ultimately enhancing the effectiveness of communication in critical situations.

    The document is approved for public release, indicating that the findings and methodologies can be shared with a broader audience, including researchers, military personnel, and communication specialists. The report emphasizes the importance of ongoing research in this area to adapt to evolving communication needs and technological advancements.

    In summary, this technical report serves as a valuable resource for understanding the relationship between speech intelligibility tests and transmission metrics, with implications for improving communication systems in military and other high-stakes environments.

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