# Do We Get What We Need from Clinical Acoustic Voice Measurements?
## 2 Background: Current State of the Art and Challenges in Clinical Acoustic Measurements
### Changes in Voice Quality Relate to \(f_{0}\) and SPL  
Several objective measures related to perceptual dysphonia, including jitter, shimmer, HNR, and CPPS, have been shown to be significantly influenced by habitual speaking voice SPL and \(f_{0}\). This was the case in sustained vowel phonation and speech in both healthy and voice-disordered individuals. When taking speaking SPL into account as a confounding variable, there were no differences between vocally healthy and matched voice-disordered women of the same age and similar professions (Figure 1) [4; 35; 36; 37; 39; 40; 41; 42; 43]. To date, there are no normative values available with correction for SPL and \(f_{0}\) for single voice quality measures or combined indices. Moreover, under the current guidelines to speak or phonate a vowel \"at comfortable loudness and pitch\", these effects are not sufficiently controlled for [4; 35; 36; 43]. From a clinical viewpoint, this leads to several pragmatic problems: patients will not necessarily speak at the same or comparable SPL and \(f_{0}\) or with the same voice quality when assessed at different points in time during the day (Figures 1 and 2) [44; 45]. Cepstral and multiparametric measures have especially been described as worse during the morning. Studies in young adults during a day and between days have partially shown a moderate test-retest reliability for several acoustic parameters, including jitter, shimmer, and CPPS [44; 45]. Moreover, in professional voice users such as teachers, an increase in mean speaking \(f_{0}\) and SPL and a reduction in jitter and shimmer during a working day have been observed [46; 47]. While not all of the observed changes are related to \(f_{0}\) and SPL,  
Figure 1: Smoothed Cepstral Peak Prominence (CPPS) with reference to sound pressure level (SPL) (@10 cm distance) in 58 voice-disordered and 58 age-matched, vocally healthy women. All phonated at individually “soft”, “comfortable”, and “loud” intensity levels. In this sample, “comfortable” phonation spanned a total range of 71–99 dB SPL (in between dashed lines) (Figure: own image, derived from [42; 43]). there is a lack of baseline data to understand which of these changes are physiologic and related to SPL and \(f_{0}\) only, and which must be classified as pathologic. Thus, patients with a lower habitual speaking voice SPL will present with reduced periodicity in voicing, which is not related to vocal impairment or lower voice quality per se (Figures 1 and 3, Table 2). Moreover, women tend to speak more softly than men in the same clinical voice tasks, which has, most likely, affected currently known normative values for gender [39; 40; 48]. Thus, basic comparability between and even within individuals is not a given, since measurements may be performed at a different speaking SPL and/or \(f_{0}\). This hinders the application of normative values for voice assessments as well as comparisons before and after treatment. Figure 3: Voice maps of Smoothed Cepstral Peak Prominence (CPPS) (dB) values for one male patient with cysts during text reading before (**left**) and after (**middle**) surgical treatment, plotted with the software FonaDyn. The (**right**) figure shows the differences between pre- and post-measurements. This figure illustrates that voice function varies by voice fundamental frequency and intensity. (Figure: provided by [PERSON], based on one individual from [42; 43]. Figure 2: Sound pressure level (SPL) distribution (@10 cm) in “soft”, “comfortable”, and “loud” phonations of 58 women with voice disorders and 58 age-matched, vocally healthy controls. The area under each curve indicates the probability (termed density) that a value will fall within the indicated interval. (Figure: own image, derived from [42; 43]). Moreover, some patients will undergo systematic changes in SPL and \(f_{0}\) through treatment. This is the case in training programs targeted at changing speaking SPL and pitch, such as Lee Silverman Voice Training or Vocal Function Exercises [49; 50].