# Influence of Piano Key Vibration Level on Players' Perception and Performance in Piano Playing
## 3 Results
### Influence of Vibration Levels on Perceived Instrument Sound, Control, and Feel
To find possible explanations for the above presented differences, we analyzed the verbal self-reports of the participants in more specific categories. We observed that the key vibrations influence the timbre and the perceived loudness of the bass keys. Also, the timbre of treble notes was judged more pleasant when playing with \(V_{2}\) or \(V_{3}\). Some participants also noted a sensation of space when playing with higher vibration levels (\(V_{2}\), \(V_{3}\)) and described it as room or reverb effect of the sound. In contrast when pianists played with vibration levels \(V_{0}\) or \(V_{1}\) the sound was sometimes described as dry. Comparisons to acoustic instruments and e-pianos also align with this observation. A critical aspect for discussion is that the sequence of parts (A, B, and C) was the same for all participants, which might have influenced the results. We designed the experiment protocol to steer the players' attention to different multi-modal aspects to discover unexpected connections between vibrotactile feedback and the players' judgment of the instrument quality. In part A the participants could freely describe their impressions and we did not suggest any quality criteria for the comparisons. Unbiased comparisons are only possible within the first part of the experiment. Ten out of eleven participants naturally made statements about sound and control in the first part, which justifies the suggestion of these criteria in the following parts. \begin{table}
\begin{tabular}{l l c c c c c} \hline \hline
**Category** & **Examples** & \(V_{0}\) & \(V_{1}\) & \(V_{2}\) & \(V_{3}\) & \(\chi^{2}\) & \(p\) \\ \hline sound pos. \(s_{p}\) & “round”, “balanced” & 21 & 26 & 39 & 24 & & \\ sound neg. \(s_{n}\) & “harsh”, “artificial” & 28 & 19 & 12 & 19 & & \\ relative number of positive statements \(s_{p}/(s_{p}+s_{n})\) & 0.4 & 0.6 & 0.8 & 0.6 & 11.86 & **0.0079** \\ \hline control pos. \(c_{p}\) & “reactive”, “controllable” & 25 & 24 & 25 & 24 & & \\ control neg. \(c_{n}\) & “limited”, “hard to create dynamics” & 15 & 11 & 13 & 16 & & \\ relative number & of positive statements \(c_{p}/(c_{p}+c_{n})\) & 0.6 & 0.7 & 0.7 & 0.6 & 0.69 & 0.88 \\ \hline feel pos. \(f_{p}\) & “comfortable”, “grand piano feeling” & 9 & 8 & 7 & 11 & & \\ feel neg. \(f_{n}\) & “exhauseting”, “tedious” & 5 & 4 & 1 & 4 & & \\ relative number & of positive statements \(f_{p}/(f_{p}+f_{n})\) & 0.6 & 0.7 & 0.9 & 0.7 & 1.52 & 0.68 \\ \hline no difference & “similar”, “somewhat different” & 12 & 24 & 11 & 13 & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Evaluation per vibration level derived from the free verbalizations of the pianists. The number of positive and negative statements per category was counted for each vibration level (\(V_{0}\), \(V_{1}\), \(V_{2}\), \(V_{3}\)). The frequency counts were evaluated with \(\chi^{2}\)-tests. The \(\chi^{2}\)-statistics and \(p\)-values are given for each category; \(p<0.05\) is highlighted in bold. We decided to put part C at the end of the experiment session, because we did not want to risk that the participants are already consciously aware of the vibrations, when comparing the levels with regard to sound. In part C the participants focused on the keyboard. Therefore we expected that it is most likely that the participants recognize the vibrations in this part (which happened in two cases). Finally, also the difficulty of the evaluation task might have altered the judgments of the pianists. In each trial, the participant played the music piece excerpt for a duration of around 30 s, communicated his or her impression with regard the previous setting and sometimes also answered clarifying questions from the experimenter. Thereafter he or she performed the music piece for the next comparison.