# Influence of Piano Key Vibration Level on Players' Perception and Performance in Piano Playing
## 1 Introduction  
Playing the piano is a complex multi-modal task, where the pianist controls the instrument through his or her intention and perceived instrument feedback. There are four main musician-musical instrument interaction modalities: visual feedback, auditory feedback, force feedback, and vibrotactile feedback. The interaction with a musical instrument can be modeled as a feedback controller [1], where the musician's brain controls his or her body, arms, and fingers to modify the instrument's behavior based on changes in sensory inputs. This closed-loop model implies that if the instrument's feedback is altered, the pianist will adapt his or her playing to compensate for and retain the desired instrument behavior. Vibrotactile feedback can support the precise control of finger force, as shown by [PERSON] [2] with a basic force repetition experiment on a rigid sensor box. Furthermore, [PERSON] and [PERSON] [3] demonstrated that tactile sensations from the finger-key surface interaction support some pianists to improve timing accuracy and precision of finger movements.  
In piano playing, vibrotactile feedback is perceived through the fingers in contact with the keys and the feet in contact with the pedals. The keybed and soundboard vibrations excite the piano keys and pedals [4]. [PERSON] and [PERSON] [5] measured the vibrations of a depressed piano key and a depressed piano pedal. Piano key vibrations comprise broadband and tonal parts [4; 6]. The tonal parts come from the string vibrations, and the broadband parts come from mechanical impacts (e.g., hammer-string impact and key-keybed impact) of the piano action when the piano key is played [4; 6].  
The levels of the vibrations' tonal part can rise to the micrometer range [7]; the vibrations are close to the limits of human vibration perception and are often sensed subconsciously [8]. However, piano key vibrations can be detected up to the middle octave of the keyboard [9]. Further, the vibration levels vary considerably among different pianos, but it remains unclear if pianists can perceive these differences [7].  
[PERSON] and [PERSON] [8] found that the ratio of broadband and tonal parts of piano key vibrations influenced the instrument's perceived sound. An upright piano was mechanically modified to reduce the broadband parts' amplitude, with the expectation to improve the instrument's quality. The pianists preferred the modification with regard to tone and loudness in an evaluation study. Interestingly, the participants did not report differences with regard to touch or vibrations.  
[PERSON] et al. [10] showed by ratings of evaluation criteria that realistic piano key vibrations rendered on a digital keyboard are preferred to a no-vibration condition. In the same study, key vibrations did not show a significant effect on pianists' timing and dynamics accuracy during a scale playing task.  
In addition to the state-of-the-art, the influence of four piano key vibration levels on pianists' personal judgment of an instrument's sound, control, and feel is investigated in this study. We designed the experiment, such that the control of vibration levels was independent of the sound of the instrument and aimed to explore connections between vibrotactile feedback and the perceived quality of the instrument. To test if pianists adapt their playing to vibrotactile feedback and to analyze if the vibrations support the control of finger forces, the effect of the vibration levels on timing and dynamics accuracy in pianists' performances is also studied in this paper.