The perceptual significance of high-frequency energy in the human voice.

Brian B Monson,Brad H Story,Andrew J Lotto,Eric J Hunter

doi:10.3389/fpsyg.2014.00587

Abstract

While human vocalizations generate acoustical energy at frequencies up to (and beyond) 20 kHz, the energy at frequencies above about 5 kHz has traditionally been neglected in speech perception research. The intent of this paper is to review (1) the historical reasons for this research trend and (2) the work that continues to elucidate the perceptual significance of high-frequency energy (HFE) in speech and singing. The historical and physical factors reveal that, while HFE was believed to be unnecessary and/or impractical for applications of interest, it was never shown to be perceptually insignificant. Rather, the main causes for focus on low-frequency energy appear to be because the low-frequency portion of the speech spectrum was seen to be sufficient (from a perceptual standpoint), or the difficulty of HFE research was too great to be justifiable (from a technological standpoint). The advancement of technology continues to overcome concerns stemming from the latter reason. Likewise, advances in our understanding of the perceptual effects of HFE now cast doubt on the first cause. Emerging evidence indicates that HFE plays a more significant role than previously believed, and should thus be considered in speech and voice perception research, especially in research involving children and the hearing impaired.

Highlights

In 1907 and 1908, the following acoustical observations were reported in Philosophical Magazine by physicist Lord Rayleigh:“The other branch of the subject, which I had hoped to treat in this paper, is the discrimination between the front and back position when a sound is observed in the open; but various obstacles have intervened to cause delay
In the century since Rayleigh’s observations, study of the acoustical energy in human speech and voice communication has typically been restricted to the frequency range below ∼5 kHz
The results from these studies addressing the acoustical and perceptual significance of highfrequency energy (HFE) indicate that, while comprising a small amount of energy in the speech and voice spectrum, HFE affects at least percepts of quality, localization, and intelligibility (Table 2)

Summary

INTRODUCTION

In 1907 and 1908, the following acoustical observations were reported in Philosophical Magazine by physicist Lord Rayleigh:. The articulation index achieved its maximal value of 1 with a cutoff frequency of 7 kHz, suggesting that HFE was unnecessary for intelligible speech These results are in part why the telephone bandwidth was restricted to a small portion of the full audio bandwidth (300– 3.4 kHz)—a specification that persists in mobile phone technology today. Some researchers have claimed the need for extending the bandwidth of augmentative hearing devices for communication purposes (e.g., Stelmachowicz et al, 2001) and some efforts are being made in this direction (Keidser et al, 2011; Moore et al, 2011) The usefulness of such bandwidth extension, and what frequency range is necessary, is still debated (reviewed in Moore et al, 2008)

ACOUSTICAL ANALYSIS OF HFE

HFE Level

Findings

CONCLUSION