As significant errors were reported in 1985 for the international standard related to equal-loudness-level contours (ELLCs) for pure tones, the earlier international standard was fully revised in 2003 as ISO 226:2003, after 18 years of revision work. Twenty years later, the standard has been revised again as ISO 226:2023. One motivation for the revision was to reflect the lowering of the threshold of hearing at 20 Hz by 0.4 dB in ISO 389-7:2019. In addition, the following two points of substance were revised: (1) implementation of the power exponent relating loudness perception to physical intensity formulated in an academic paper published in 2004, which describes the derivation of ELLCs relating to ISO 226:2003, and (2) adoption of mathematical expressions that preserve the appropriate number of significant digits. In this review, the process of the revision and the technical details of the changes are described. The differences from the 2003 edition are only 0.6 dB at most, and the 2023 standard can be regarded as the same as the 2003 edition in terms of practical use.

Propagation of waves in poroelastic media is of interest in various fields, including acoustics of marine sediments, bone, and absorbing materials, geophysics, and civil engineering. Biot's theory provides the most comprehensive description of this type of wave propagation that includes inherent coupling of the solid and fluid components of such media. This review paper presents an introductory guide to Biot's theory of poroelastic wave propagation.

To clarify Japanese and Korean speakers' perception characteristics of the Japanese fricative /s/ and affricate /ʦ/, a perception experiment was conducted in which 40 Japanese and 40 Korean speakers made a two-alternative forced choice for the /s/–/ʦ/ stimulus continuum developed by modifying the rise and steady+decay durations of frication. The Korean speakers' perceptual boundary of /s/ and /ʦ/ was similar to, but slightly different from, that of Japanese speakers, and their discrimination sensitivity was lower than that of Japanese speakers. However, Korean speakers' perception of these consonants was fairly good, even though /ʦ/ is not a phoneme of the Korean language. The results suggest that Korean speakers can apply the acoustic features of Korean fricatives and affricates to perceive the Japanese /s/ as well as /ʦ/ that does not exist in their first language.

Voice recognition plays an important role in everyday life. In this study, we sought to examine the effects of wearing a face mask on a speaker's acoustic parameters and the perceiver's evaluation of voice attractiveness. The masked and unmasked voices of 22 participants were analyzed through acoustic measures and were used as stimuli for 27 individuals to rate attractiveness. The results suggest that the mask had no noticeable impact on the time-domain glottal flow or aperiodicity parameters of the voices. However, there appears to be an influence on spectral parameters, specifically energy (for both genders) and H1–H2 (for women), as well as H1–A3 (for women). These spectral parameters were successfully identified by raters, who rated voice clips recorded without masks as significantly more attractive compared to those recorded while wearing masks. In conclusion, wearing a mask may have a slight effect on the ratings of women's voices. These ratings are congruent with acoustic measurements.

Lombard speech is known to make it easier for listeners to perceive speech signals in the presence of background noise. The aim of this study was to investigate how temporal characteristics such as the temporal envelope and temporal fine structure (TFS) in Lombard speech contribute to improve the segregation of Lombard speech from background noises. In the speech production task, we confirmed that Lombard speech had increased low-frequency amplitude modulations in the temporal envelope and increased frequency modulations in TFS compared to plain speech in frequency ranges covering first and second formants. In a speech perception task, ease of speech segregation was compared between Lombard and plain speech. We also compared ease of segregation of tone-vocoded speech created from Lombard and plain speech to examine the effect of eliminating TFS. We found that Lombard speech with both high amplitude and frequency modulations had improved speech segregation in both original and tone-vocoded speech conditions, but the difference in ease of speech segregation between Lombard and plain speech tended to be larger in original speech than tone-vocoded speech conditions. The present findings suggest that an enhanced envelope is the main contributor to improved segregation of Lombard speech, while increased frequency modulation plays a complementary role.