In contrast to performers on other string instruments, like the violinist or the guitar player, the pianist could be said to only have an indirect control of the string excitation. Using the computer biased terminology of today, it is tempting to call the action an "interface" between the pianist and the string. This interface is an interconnecting device, which at the input end (the keys) is particularly adapted to the soft and sensitive fingers of the pianist, while the output end is equipped with hard felt hammers, capable of exciting even the thickest of the tense piano strings vigorously. The function of this "interface" in playing is by no means simple.

Nothing definite can be said yet about the pianist's ability to influence the tone quality by controlling the motion of the hammer. It is true that the entire history of the hammer motion during acceleration can be very different depending on the way the key is depressed (cf. Fig. 11). But this observation does not automatically imply that the interaction between hammer and string is influenced in some way. As mentioned, the hammer is flying freely the final distance before string contact. However, we have recently observed that the motion of the freely flying hammer can be somewhat different for slightly different types of touch (see Fig. 14). This is due to the "ripple" resonance, which is seen to influence the hammer motion during the last milliseconds before string contact, i.e. after "let-off." In this way, it is possible that a hammer resonance could serve as a "memory" of the history of the hammer motion. This would allow the pianist to have at least an indirect influence on the very final part of the hammer motion, even after mechanical contact between key and hammer has ceased.

However, we still have to be very careful in the interpretation of these results. Although the observations suggest that the hammer can make a rubbing motion against the string during contact, it has not yet been shown that such a motion takes place. Even if it does, it remains to be shown that a motion of this kind could influence the string excitation and hence the tone quality.
In summarizing the present results, we cannot rule out the possibility that the pianist's touch may have an influence on the character of the piano tone. As regards the initial "thump" it seems rather clear that it contributes to the character of the note, while an actual influence on the tone character via the hammer motion has not been verified yet.

• 音量，由振幅决定，是物体离开平衡位置的最大距离，简单理解可以认为是波峰到中线的距离，在乐器演奏中的强弱就能改变这点，轻轻弹，则音量小，加重弹，则音量大。
  
• 音高，由主频（基频）的振动频率决定，也就是机械波里的振动频率，这个频率由琴弦本身长短和松紧来调整，弦越长，越松，频率会越低，在钢琴上这个事情由制造商和调律师来解决，钢琴家并不参与。
  
• 音色，由泛音决定，什么是泛音？琴弦产生的都是驻波，驻波不仅仅有主频（基频），还会使琴弦得到2倍、3倍……的频率，而这些高倍的频率就是泛音。也就是说当你弹下一个琴键的时候，不只是这个音在按照基频在振动，它的2倍、3倍……频率也在同时振动。
  

• 两个音一样重，声音听起来比较“直白”，“自然”；
  
• 高音重，低音轻，声音听起来比较“亮”，“金属般光泽”；
  
• 低音重，高音轻，声音听起来比较“闷”，“柔”。
  

Depending on the touch, the motion of the hammer can be quite different, even when the dynamic level is kept constant. The examples in Fig. 11 show the hammer velocity and acceleration for three different types of touch as measured at the hammer head. Indeed, the motion of the hammer before string contact is different in the three examples, despite the fact that the final velocities were approximately the same. At the moment it may suffice to note that the hammer motion seems to involve two components of oscillation, which are excited differently depending on the touch. One is a slow "backwash" motion at about 50 Hz and the other is a "ripple" type motion at about 400 Hz. While the slow motion is more prominent in the gentle types of touch, the "ripple" motion seems to be a characteristic of the vigorous, impulse-like types of touch.

Fig. 11. Influence of different types of touch on the hammer motion (acceleration and velocity) mezzo forte, B3. The pianist described the types as: "middle finger only" (top), "heavy arm with relaxed finger" (middle), "heavy arm with strained finger" (bottom).