Current Trends and Future Directions in Voice Acoustics Measurement

Dear Colleagues,

The human voice production mechanism implements a superbly rich communication channel that at once tells us what, who, how, and much more. This is thanks to its many degrees of freedom and its large variability. This same variability, however, presents a multitude of challenges in using the sound of the voice for making clinical voice assessments. Decades of research notwithstanding, many acoustic and other physical measures of voice are still not solidly established as clinical evidence, and this is true even though experienced clinicians can often hear what the problem is. There are several underlying reasons for this situation.

First, there appears to be a divide between, on the one hand, enthusiastic engineers continually searching for new voice metrics and pathology classification schemes, and on the other, pragmatic clinicians ever struggling to understand the metrics on offer, in the hope that essential quantitative evidence might be produced for the efficacy of treatments. It has long been clear that this divide must be bridged if real progress is to be made. The inherent complexity of voice production and its disorders makes this difficult but not impossible.

Second, there appears to be a lack of a common understanding of how variable the voice can be. The amount of normal and pathological variation both between and within individuals has profound consequences for how to elicit and sample vocal productions. Once this has been agreed upon, we can proceed to agree on how to negotiate this variability.

Third, it is not easy to generate a market pull for new methods that is sufficient for the healthcare tech industry to engage. There is no lack of voice metrics: there are already hundreds of them in the literature, and physicists, mathematicians, and engineers love to come up with new ones. However, very few of these people love to run the ensuing gauntlet of commercial deployment. Many clever ideas, perhaps even most of them, tend to fizzle out when the engineering students who prototyped them move on. Investors and industry, from which the serious resources must come, are not tempted to engage unless they see enough of a market pull to establish a critical mass of customers in clinical speech and voice care. Such a market pull presupposes not only proven practice and clinical consensus, but also interoperable technical and medical standards, regulations, and legislation, and not least persuading decision-makers at different levels of the health sector that investing in progress will increase productivity within their own domain. Resolving this chicken-and-egg situation amounts to a very tall order, beyond the remit of any single agency, and so voice analysis tends to move along as best it can, in academic labs and conferences. Can voice analysis find a way out into the world, there to earn its keep? The administrative wisdom and clout needed for implementing a productive set of top–down policies and incentives appear to be in short supply almost everywhere. Perhaps, however, many bottom–up efforts and proofs of principle could muster the critical mass, if researchers and clinicians can get their acts together even more. With this Special Issue, we attempt to sketch some inspirational input to such an effort.

Surely, we should not need more metrics. Rather, in order to achieve more expeditious clinical uptake and research advances, we need to identify the most useful metrics and methods, and learn how best to adopt them in stringent and deployable ways. This Special Issue also discusses how voice data—mostly acoustic—would need to be collected, analyzed, and interpreted in order to improve the evidential value of objective measurements. Although the focus here is on acoustic measures, for their convenient non-invasive nature, the ideas are equally applicable to measures from physiology, biomechanics, image processing, and aerodynamics. Indeed, it is probably through the intelligent collation of multimodal measurements that the voice will reveal essential aspects of its function.

In this Special Issue on Voice Acoustics Measurement, the contributors report not only on making various innovative measurements, but also on the more general and fundamentally important issues of acquisition, sampling, statistics, and clinical relevance. We believe these to be essential stepping stones to the achievement of broad clinical uptake and industrial engagement, which in turn are necessary for energizing continued advancement in voice research. New measurement paradigms, critical appraisals, fresh perspectives, and broad collaborations are encouraged. We thank all contributing authors in the present Issue for giving fine examples of such initiatives.

Prof. Dr. Sten Ternström
Guest Editor

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• voice acoustics
• voice measurement
• variability
• phonation
• voice production
• measurement sampling
• voice maps
• clinical relevance
• machine learning