# Voice Maps as a Tool for Understanding and Dealing with Variability in the Voice
## 3 Voice Maps in Practice
### Mapping Effects of Interventions  
By using voice mapping, and ensuring that productions elicited pre- and post-intervention will overlap each other in the voice field, at least within a relevant range, it is possible to compare outcomes within subjects at _matched_ SPL and _matched_\(f_{\text{o}}\). In so doing, we can elegantly eliminate the influence of \"elicitation noise\", and at the same time account for the person-specific trends in the given voice. An example is given in Figure 5. A transgender patient read a standard text for about two minutes, before feminization therapy, and then was recorded again 3 months post-therapy. It is very important when making such recordings to keep the setup, gain calibration, protocol and/or task identical, pre- and post-therapy. The top row shows the density, i.e., the number of cycles phonated in each cell. It can be seen that her speech range and its distribution mode were translated upwards, in both sound level and \(f_{\text{o}}\). The _difference map_ (c) at the right shows the cell-by-cell differences in the overlapping region, i.e., in those cells that were populated in both the pre- and post-therapy maps. Here red signifies fewer cycles; green signifies more cycles. Clearly, after therapy, the patient spent more of the task time at \(\text{high}\,f_{\text{o}}\); and we would not have needed a voice map to establish that. However, consider now the bottom row in Figure 5, which shows the average spectrum balance of the voiced segments only. In the difference map (f), the consistency of the green area signifies that there has been a physiological change, resulting in more energy above 2 kHz, in the post-therapy condition. The average difference in all the cells in (f) is +4 dB. Such a change could have been brought on by a regrouping of formant frequencies, and/or by a somewhat more pressed use of the voice. Thanks to the mapping, however, we know that the cause of this increase is _not_ a higher SPL nor a higher \(f_{\text{o}}\) (both of which are known also to affect the spectrum balance), since the SB in each cell of the \"post\" map (e) is compared to the corresponding cell in the \"pre\" map (d). Also, measuring only a few sustained vowels would not have given such a clear outcome. Another application of difference maps is to investigate subtle changes in highly controlled tasks, as with professional singers. In this situation, there is little or no elicitation  
Figure 5: Examples of maps across an intervention. A patient read for two minutes from _The North Wind and the Sun_, in Swedish, before and after feminization therapy. Top row: the density, i.e., the number of cycles phonated (**a**) before therapy, (**b**) after therapy, and (**c**) the difference. Bottom row, the spectrum balance SB (level > 2 kHz – level < 1.5 kHz), (**d**) before therapy, (**e**) after therapy, and (**f**) the difference in the overlapping region. The ovals approximating the overlap region are all in the same place, given for visual reference only. In that region, each cell contained an average count of 22 phonatory cycles. After therapy (**f**), the mean SB had increased by 4 dB in the region of the voice range that was visited both pre- and post-intervention. noise, and the effect sizes may be very small, yet of interest. An example can be found in a recent study on using the flow-ball as a feedback device for learning breath control [44]. Trained singers did a soft-loud-soft exercise on the vowel /a:/, first normally, then while phonating into a flow-ball (the intervention), and then immediately again without the flow-ball. This was repeated in whole-tone steps increasing over \(1\frac{1}{2}\) octaves, so there was one intervention for every tone in the scale. The full voice range was not explored. The top row of Figure 6 shows maps of the EGG contact quotient \(Q_{\text{ci}}\) on a colour scale, for a trained baritone. The pre- and post-intervention maps look quite similar, but the third map reveals the _differences_ after the intervention.