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Piano Technique - Theory

5. Characteristics of the keyboard and its mechanical parameters

5.1. Basic parameters
The images on the right and below (hover with the cursor) show us basically a longitudinal section of the key.

Fig. 1a - caption
= Key at rest
= Key engaged
Level A - key at rest, in its upper position;
Level B - level of the double escapement, (the mechanism which permits quick repetition). When slowly pressing on a key of a grand piano, one feels at this point a slight supplementary resistance that is not perceived when the key is struck more rapidly, i.e. during a normal strike;
Level C - “at the bottom” of the key, i.e. at the maximum depth of its descent;
D - a felt pad that reduces the noise of the key against the piano’s key frame.
N.B. The common term “stiffness of the keyboard” refers to the key’s resistance mechanism. To overcome this resistance (with the pedal depressed thus eliminating the weight of the damper) a weight of 50 to 70 g1 (contemporary sources give measures of 60 to 80 g) is needed. As a comparison: the weight of a finger varies normally between 12 and 30 grams2.
1 Czesław Sielużycki - “The pianist’s hand” p. 211, Polish Music Edition, Cracow, 1982
2 Op. cit. p. 120
These figures, quoted from the work of Cz. Sielużycki, are not absolute values, because:
● As it is likely that Sielużycki borrowed references the work of T. Matthay (coincidence with numbers), dating from shortly before the 1930s, the keyboard depth of modern pianos can be a little different. One must remember that the pianos of Chopin’s time had a mechanical keyboard depth almost two times less, compared to modern instruments of the 20th century (Schelling3);
● they may vary slightly depending on the brand of the instrument;
● when a key is pressed more strongly, the compression of the felt D will be greater, as will be the key depth. I mention these values for guidance only, as it is the working principle that is important and not the numbers. One must also remember the relativity of the numbers defining levels in the keyboard: the bottom of the black keys is more than 10 mm higher than that of white ones. Therefore, the so-called “smooth and even playing” is performed on two different levels.
3 Jean-Jacques Eigeldinger - “Chopin: Pianist and Teacher as Seen by His Pupils”, Cambridge University Press, Cambridge 1986

5.2. Normal working of the key
Fig. 1c shows the key fully depressed
IMPORTANT! The pianist can control the movement of the hammer only until the line B, which is about ¾ of the AC depth. The hammer travels “alone” for the last quarter of the way to the string only by the force of its trajectory. At this point, the repeating mechanism breaks its contact with the key (Sielużycki4). Without underestimating the importance of hand’s pressure to the keybed, it must be taken into account that this pressure does not comes until after the beginning of the sound.
Conclusion: the sound is produced by the movement of transmission of the units extending from the shoulder to the fingers (“The Bridge”), while an eventual pressure at the bottom of the key only determines the next sound. In practice, this difference is so small that one can not, in principle, account for it. But it is important to understand this succession of movements so as to be able to solve certain particular technical difficulties (see the following).
4 Czesław Sielużycki - op. cit. p. 211

5.3. The key does not strike completely (advanced technique)
Fig. 1b - the key is pressed only to level B.
The keyboard characteristic presented in paragraph 5.2 is used in a special technique that involves pressing the keys not completely to the bottom, but only up to level B, that corresponds to the minimum pressure needed in order to obtain a sound (Sielużycki5). Obviously, this has nothing to do with superficial playing resulting in a poor sound quality. The difference is the amount of energy (mass) used to produce the sound and how to transmit this energy to the mechanism of the piano: a beginning student using only the mass of the fingers, hand and possibly the forearm, produces an uneven and thin sound. On the other hand, an experienced pianist uses the large mass of the entire motor apparatus, so that even his ppp sounds amply.
To return to the technique of partially depressed keys: thus, for each note , the pianist can gain between 2 and 3 mm, which, with a speed of about a dozen notes per second, provides a significant economy of energy. Since this technique deprives the hand resting on the bottom of the key, it is necessary to use the inertia of the keyboard. That is why it is the pianos with a „stiffer” keyboard that best allow this technique. This way of playing requires perfect mastery of “hovering” over the keyboard that makes very proficient use of the motor appparatus on two planes: horizontal and above all vertical. So that the sound becomes balanced, all keys must be pressed not only with the same speed, but also to the same key depth.
5 Czesław Sielużycki - op. cit. p. 211

5.4. Rapid repetition (advanced technique)
Fig. 1b’ - the key vibrates around the level B’. That is to say, not only it is important not to press the key down to the keybed (cf. the preceding point) but also one must not release it completely so it returns to the resting level A.
In the preceding paragraph we dealt with the question of the key struck lightly, without being pressed down to the bottom of the key. Here, on the contrary, one must strike it again before it returns to its original state of rest. Nonetheless one must precisely measure the amplitude of the movement and feel its sensations through the fingertips, because if we press down “too deeply” (between levels B and C) certain keys may produce no sound. Therefore, one must slightly raise the level of attack from the line B towards the line B’ that is approximately 6.5 mm lower than the upper surface of the keys. On the other hand, playing that is “too flat” (i.e. the key raised above the level B’ results in a loss of speed, because the hammer will descend too low.
In other words: playing with a finger strike that is either too shallow or too deep keeps us from accomplishing clear and precise repeated notes. To better understand, see diagram below:
level A ¯¯¯¯¯ = key at rest
level B’’ ––––– = key at halfway down, but not enough (too high) for repetitions
level B’ ––––– = key at halfway down: OPTIMAL for repetitions
level B ––––– = key at halfway down, but too much (too low) for repetitions
level C _____ = key engaged
With a properly balanced finger strike, the repeated key is lowered by only about 3 mm and thus the distance of the hammer to the strings is considerably shortened. In this way it doesn’t fall on the backcheck and stops much closer to the string because of the double escapement, reducing its inertia. It is thus that we obtain a repetition rate close to 15 notes per second by playing:
● with one hand, using the fingerings 12, 13, 123 or in their reverse order;
● RH/LH alternating (fastest and easiest option);
● a single finger, permitting the vibration of the entire motor apparatus (the most difficult option - cf. Chapter 10).


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