The Point of Sound or, Why an Acoustic Piano is Not Interchangeable With a Digital
A question that frequently gets asked by parents and pianists alike is whether a digital piano is interchangeable with an acoustic for learning to play the piano. The answer, with rare exceptions, is no.
Often it is believed that if there are 88 keys and they are weighted that is all that is required to imitate a piano. But an essential feature missing from all but a few high end digitals is the escapement mechanism. It is the escapement that allows us to draw out an seemingly endless range of nuances from the instrument and it is the escapement that does much of the work for us in technically challenging passages.
1.What is the Escapement Mechanism?
For a detailed explanation of all of the parts of the piano and its action check out Christopher Smit’s “The Piano Deconstructed” page. But here’s a brief summary:
A. Bartolomeo Cristofori and the Single Escapement Action
When Cristofori invented the piano in 1700 his most important innovation was the piano action. In earlier keyboard instruments like the harpsichord, the keyboardist depresses a key and a quill plucks the string. This allows for considerable overall volume in public performances but regardless of how slow or fast a key is played, the dynamic level remains the same.
Sound at the clavichord is produced by small metal blades called tangents which strike brass or metal strings from above. Until the player lifts their finger off the key the tangent stays in contact with the string. The clavichord can create many dynamic nuances and even vibrato, but the overall volume of the instrument is so soft that it is only suitable for home use.
With the invention of the pianoforte, the keyboardist had an instrument that could play both loud and soft on a single key and produced enough sound to be used in public performance. This was thanks to the escapement action. When the pianist plays the key, the hammers strike the string rapidly. Unlike the clavichord, the hammer immediately rebounds off the string while the key is still depressed. The slower the pianist plays into the key the softer the sound. The faster into the key the louder the sound. Degrees of volume are created by velocity, not force.
B. Sébastien Erard and the Double Escapement
Invented in 1821 by Erard, the double escapement made it possible to rapidly repeat a key. The addition of a repetition spring and other components meant that the hammer could “reload” allowing for multiple hammer repetitions without fully releasing a key. Composers of the Romantic era exploited this capability filling their music with repeated notes and chords, octaves, double notes, and tremolos pushing the limits of virtuosity at the keyboard to its extreme.
https://www.youtube.com/watch?v=PAKtfkh0C1M
2. Tonal nuance
Near the bottom of the piano key there is a little bump. This is the escapement level at which point the hammer strikes the string. Dorothy Taubman called this the “point of sound.” After the sound has been produced there is nothing we can do to alter it.
On a well regulated piano the point of sound should be about a pennie’s width higher than than keybed.
Past the bump there is a little bit of space called the ‘aftertouch.” Ideally the pianist aims for the point of sound and then follows through the aftertouch to the bottom of the key.
All tonal control is a result of the pianist’s relationship with the point of sound. Hindemith said that “it makes no difference on the piano whether it is touched with the tip of an umbrella or with the finger of Arthur Rubinstein.” But this fails to take into account how sensitive the instrument is. Even on a single note, an enormous range of volumes and tonal qualities can be produced.
As Thomas Marks notes in his book. “What Every Pianist Needs to Know About the Body“: “Volume of sound is not the only thing that changes: as the hammer goes faster and faster or slower, the mix of overtones shift also, so the quality of the sound changes as well as the volume. ”
If the finger plays too fast into the key a harsh sound is produced.
Too slowly, none at all.
3. Helping students find the point of sound
To find the point of sound depress the key slowly until the bump can be felt and then play to the bottom of the key. Often young students are impatient and will take a few tries to drop slowly enough to feel the bump. Once the student has found the point of sound they can practice dropping faster or slower into a key to change the dynamic level.
Avoiding keybedding: The hallmark of virtuoso playing is minimal effort for maximal effect. A poor habit common to pianists is pressing against the keybed after the sound has been produced. This is true amongst children who believe that volume is created by force. But it is also true among professionals, particularly when they are emotionally involved.
As Tobias Matthay wrote, “the keybeds are not like ripe fruit out of which sound-juice can squeezed.”
To help the student feel how much effort is necessary I use a trick shown to me by Dr. Teresa Dybvig. I depress the keys and have the student play on top of them. If there is a “thud” I know they are working too hard.
Renowned hand therapist Dr. Caryl Johnson often recommended pianists practice on a table top to avoid using excess force.
4. Rebounding off the key
In addition to tonal nuance the double escapement has to ability to rebound the hand in staccato passages, octaves, and chords much like bouncing on a trampoline. Gravity takes care of the down, the rebound the up. Without an aftertouch the pianist is forced to use the fingers to depress the full weight of the hammer and has to lug the arm around the piano rather than allowing it to be bounced from place to place.
Poorly regulated or nonexistent escapement is a major cause of injury at the keyboard. Playing without an escapement mechanism is equivalent to jumping on asphalt rather than a trampoline. I can play for hours on an acoustic piano without fatigue but I often find I’m sore after playing a gig using a digital keyboard due to the lack of a point of sound.
5. Helping students to rebound
Helping students to rebound off the key is similar to finding the point of sound:
a. The student feels the ‘bump’;
b. The student rests on the bottom of the key;
c. The student slowly rides it to top as if it were an elevator.
Gradually the speed can be increased. If the student’s finger-hand-forearm unit is balanced well over the key, the repetition lever will do all the work for them. It is not even necessary to leave the surface of the key when practicing this.
This skill is essential for any non legato touch including octave, repeated notes, chords, and staccato.
Having students clap their hands together or pretend to dribble a basketball will further reinforce this image of the bouncing finger-hand-forearm unit.
6. Special effects using the point of sound
The most efficient way to play a key is to aim for the point of sound and follow through with the arm to the bottom of the keybed at which point all downward motion stops.
However, there are places in the repertoire where a bell-like sound can be created by playing only to the point of sound. This is quite effective in impressionist music like Debussy and Ravel as in the ‘Bells” of Ravel’s “La Vallee des Cloches”
or for the wedge notes in the opening of Beethoven op. 110.
Brilliant passages like rapid alternating octaves can also benefit from this approach.
7. Acoustic or digital?
I hope I have made a case for the necessity of a well-regulated escapement mechanism during all stages of piano study. It is only fair to note that there are a few hybrid digital-acoustic instruments on the market which have a hammer action modeled after the piano. I haven’t had the opportunity to try them all but if you are in the market for a digital instrument I would only recommend purchasing one of these.
The action on an upright is a little different than a grand. Most do not have a double escapement but rather an additional spring to mimic the action of a grand. In general, a grand will have a better action with faster repetitions, but a high quality upright is preferable to a poor quality grand.
If you can’t find the point of sound on your acoustic or the aftertouch feels too shallow or too deep it is worth contacting a certified piano technician.
Please let me know if you enjoyed this post. Questions and comments welcomed!