# Voice Maps as a Tool for Understanding and Dealing with Variability in the Voice
## 2 Aspects of Variability in Voice
### Reproducibility and Elicitation  
Legacy assessment paradigms tend to rely on the measurement of properties of individual sustained vowel sounds. It is common practice to elicit a vowel at \"comfortable pitch and loudness\", without noting the SPL or \(f_{\mathrm{o}}\) that results. If this is repeated, perhaps weeks later, without any intervention, how similar will the second production be to the first? Surprisingly, this appears to have been studied only sparingly. [PERSON] et al. [36] studied the repeatability in elicited \"comfortable\" SPL and \(f_{\mathrm{o}}\) of 16 speakers across several days and found it to be poor, with the standard deviation in \"relative\" SPL within speakers being 4.7 dB and about 10 dB between speakers; while spontaneous/\(f_{\mathrm{o}}\) exhibited a standard deviation of some 1-2 semitones. They recommended tighter control of SPL and \(f_{\mathrm{o}}\) when eliciting phonation, and to include them as experimental factors--but few have since taken notice. A later article on the reliability [37] of test-retest at \"comfortable loudness and pitch\" after one week (30 \(\circ\), 30 \(\circ\)) found that reliability was very good at the group level; however, the authors noted that the group level is not relevant for assessing a change in a given patient. Another study, on the test-retest reliability of aerodynamic measures [38] found that the intra-subject minimum difference MD (the smallest observed difference to be regarded as real for a given subject, given the variability in elicitation) was 5 dB in SPL and 3 semitones in/\(f_{\mathrm{o}}\). Voice mapping reveals that even such apparently modest differences can significantly influence metrics that trend with SPL or \(f_{\mathrm{o}}\), and most of them do. In other words, test-retest reliability _cannot_ be assumed to be good. [PERSON] et al. [39] examined changes in the CPPs as related to SPL and \(f_{\mathrm{o}}\) at three levels of elicitation. Some of their SPL results are shown in Figure 3 (round markers). For the present article, we have looked also at a database that was collected for other purposes, of isolated sustained vowel sounds elicited at \"soft\", \"comfortable\" and \"loud\" effort levels. That data collection was done according to best practice. The raw data have kindly been made available to us by the researchers, who have published several peer-reviewed studies based on that data set [16; 17]. The collection was done pre-intervention (therapy or surgery), and then post-intervention. Looking at a subset of this database (85 female voice patients, /a/ vowels only, pre-intervention), we consider first the means and standard deviations in SPL for the three elicitations (Figure 3, square markers). The two cohorts shown in Figure 3 responded similarly to the template elicitations, with a 6 dB or 8 dB increment between the steps, although with rather large standard deviations, resulting in considerable SPL overlap between the effort levels. Many of the patients in cohort 2 had an intervention and then returned for another recording session. Figure 4 shows the correlation plots of what 58 such participants did in the pre- and post-intervention recording sessions #1 and #2, for the same elicitations, in SPL and in \(f_{\text{o}}\). The SPL produced by any given participant showed a mean absolute difference of 4.3 dB between the two occasions, while the mean absolute difference in \(f_{\text{o}}\) was 2.4 semitones. There was no effect of intervention #1 versus #2 on \(f_{\text{o}}\) (+0.37 semitones, \(p=0.53\)) and only a weak effect on SPL (\(-0.76\) dB, \(p=0.049\)). Given that the task was the same in the two sessions, one might expect some correlation between the responses, but these correlations are low, especially in SPL. It can be seen in Figure 4 that repeated productions of a participant could differ by as much as \(\pm 10\) dB or \(\pm 10\) semitones between sessions, _for the same elicitation_.