Demystifying Piano Tone

For generations – centuries even – pianists have sought the secret to playing with a beautiful tone. Teachers have attributed a beautiful sound to a certain type of hand and shape of the fingers, to touching the key with the “fleshy” part of the finger, to playing with curved rather than flat fingers, and other purported factors.

I’ve seen pianists wiggling their finger while holding a key, similar to the way string players play vibrato. Yet vibrato is impossible on a piano because the strings are under literally tons of tension! Moreover, once the hammer strikes the strings it bounces off, allowing the strings to vibrate. This means that there’s simply nothing we can do while holding a key to affect its pitch after the fact.

I’ve also seen some pianists sliding the fingers towards the back of the keys while holding a chord. I’ve even seen this taught – by very famous teachers at that – as an expressive technique. Again, however, this can do nothing to change the sound once the keys have been pressed.

Some pianists insist that whether or not we release a key while the sustain pedal is held is an important contributor to a beautiful piano sound – of that key. But this claim contradicts the very nature of the sustain pedal. When we press the sustain pedal, the dampers are raised so that the strings can continue to vibrate. The very purpose of the sustain pedal is to allow us to release the key so that the hand is free to play other notes while the original key continues to sound. Aside from the faint mechanical noise of releasing the key, which is inaudible if we release it slowly, it’s not possible to affect the sound of that note while the sustain pedal is held.

On a piano, once a note is played, except for introducing extraneous noises, we can do nothing to affect its sound short of pressing the sustain pedal to add a touch of resonance due to the sympathetic vibration of other strings. The piano is actually quite limited in its expressive possibilities compared to many instruments. Pitches on a piano are fixed, the piano cannot play a vibrato, and it can’t even play perfectly in tune. Even the tuning of a piano is by nature a matter of compromise. It’s not possible to play a crescendo on a single note, since once we press the key, that note only gets softer. On most other instruments, it’s possible to play a crescendo or decrescendo as desired while continuing to play the note. Given all these compromises, it’s indeed a wonder that it is possible to make a piano sound lyrical at all, yet this is precisely what masters are able to achieve.

On the other hand, mechanical noises from the fingers and piano should not be underestimated. In fact, the sound of the fingers hitting the keys can be quite noisy. Pressing a piano key with another object – a metal coin, for instance – will make a loud sound a few milliseconds before we hear the tone from the strings. If the fingernails are too long, the sound of the fingernails hitting the keys can be quite distracting. (Piano teachers often have to beg their teenage students to trim their nails!)

Similarly, it’s possible to release the keys “fortissimo,” letting them go all of a sudden rather than controlling the release. If we release the keys too quickly, the piano also makes a noise that might affect how beautiful the overall tone is perceived.

Overtones

I’ve quite often heard it claimed by professional pianists that the way we strike a key can affect the overtones of the sound. The claim is that it is possible to play a single note at the exact same dynamic level but with different overtones depending on how we strike the key: If we strike it insensitively, the piano will output the fundamental but the overtones will be compromised; if we strike the key sensitively, the resulting note will be richer in overtones.

However, this theory fails to hold up to scrutiny. One “fundamental” reason is that the instrument by its nature is acoustically complex: For bass notes in the first several octaves, the fundamental tone can be indistinguishable when measured or barely present, dwarfed by the much higher intensity of the overtones of that note. (Obviously this will depend in part on the size of the piano: An upright piano cannot exhibit the deep bass of a concert grand.)

The action of a modern piano (and the piano has been “modern” for well over a century at this point) has far too many parts for anything striking the key to affect the overtones. The key itself is but a lever that triggers a complex series of actions when pressed. The principle behind a grand piano’s action is the conversion of the relatively small distance a key is pressed to a sound of variable intensity, depending on how hard the key is pressed. The finger presses the end of the lever (the key), which then “throws” the hammer toward the strings; the lever is decoupled from the hammer to make it possible for the strings to continue vibrating while holding the key.

The only variable that ultimately determines the sound is the velocity with which the hammer strikes the strings. This determines how much the strings vibrate – their amplitude – and hence the volume of that note. (How fast the strings vibrate – their pitch – is determined by their length, thickness and tuning, or how much they’re stretched.) The overtones of any piano string are similarly determined by how hard the hammer strikes the strings. This means that for each string, for any amplitude there is a given overtone series. On modern pianos this can be demonstrated using reproducing piano technology and measuring instruments.

Scientific experiments

Scientists have even gone so far as to conduct blind tests in which a professional pianist plays a note and the same note is played by an amateur pianist or even an inanimate object.

In 2014 two experiments were performed jointly by three music conservatories, in Vienna, Stockholm and Quebec. The researchers concluded that musicians could in fact detect mechanical noises that affected their perception of tone quality. These included the sound of the finger striking the key and the sound of the key hitting the key bed. In the experiments, the speed of the hammer was measurably held constant, meaning that the hammer struck the strings at exactly the same velocity, thus eliminating the possibility of slightly different volumes accounting for any differences detected by listeners.

(It’s worth pointing out that these experiments were performed using recently built pianos, whose mechanisms can differ from 19th- and certainly 18th-century pianos. On some types of action of the time, hammers would rebound and some suspected the hammers of striking the strings again, which the action was in any case supposed to prevent.)

In both of these experiments, participants listened, using headphones, to recordings of notes played with and without these noises. They were free to adjust the playback volume as desired – and hence amplify any effects. Microphones were placed very close to the piano strings in both cases, and in the second experiment (regarding the sound of the keys “bottoming out,” or hitting the key bed) a second microphone was placed close to the keyboard.

Unsurprisingly, trained musicians were able to detect the sound of the finger hitting the key and the sound of the key hitting the key bed under these experimental conditions. The researchers concluded that the experiments lend credence to musicians’ view that the way pianists touch the keys have an effect on the sound quality, even when the exact dynamic level is held constant.

A counterargument to the second experiment is that listeners never sit with their ears right next to the keyboard and microphones are never placed mere inches from the keyboard. Recording engineers don’t want to capture the nonmusical sounds of the fingers hitting the keys or the keys bottoming out. They want to capture the tone of the piano, the strings and soundboard vibrating. Furthermore, amplifying the playback volume can exaggerate any effects.

It’s also doubtful whether any of these extraneous sounds – the finger hitting the key, the key reaching the bottom of the key bed, or others such as the release of the key – are audible at normal listening distances. From the last row in the gallery of a 2000-seat concert hall the beauty or harshness of a concert pianist’s tone is immediately evident. Surely this cannot be due to extraneous sounds that are very difficult to discern at close range and need to be amplified and played over headphones. There must be another factor.

What influences the piano’s sound?

If the sound of a note on the piano merely comes down to how fast the hammer strikes the strings, is there anything else that can affect the piano’s sound? What does have an influence on sound?

While the volume of a note can stay the same, extraneous noises can affect the perceived tone quality. Fingernails, as mentioned above, can be heard hitting the keys if they’re too long. This is why pianists need to keep their fingernails short and neatly trimmed. I’ve even heard recordings in which the pianist’s fingernails are clearly audible, which I find distracting.

Another extraneous noise is “key bedding.” This refers to the sound of the key hitting the bottom of the key bed. A piano key can only go down so far. Trying to push them past this point by pressing too hard can create mechanical noise that sometimes can be heard. This can create an unpleasant noise that can affect the subjective tone. More importantly, “key bedding” creates unnecessary tension. Tension has a major effect on tone quality. Through professional training, pianists should get to know the difference between a proper tenuto, involving holding the keys without unnecessary tension, and trying to press the keys beyond the point which they can go.

That said, it is possible to play a perfectly beautiful sound with tons of unnecessary physical tension, provided that we’re playing one note at a time or a technically simple passage. If the music becomes complex or fast, however, extra tension can and usually does translate into sound. Most often, too much tension causes us to play too loud and limits our speed. Unnecessary tension limits our ability to control softer sounds at fast speeds. This can sound harsh.

Single notes vs. multiple notes

As a musician, I think too much attention has been given in this debate to the tone of individual notes on the piano. While a single note may sound out of place or even ugly, it always depends on the musical context. If you play a soft melody and one note is clearly way too loud, that note will sound “ugly.” Yet that same note played the same way at the same volume in another melody might sound breathtakingly beautiful. Everything depends on the musical context, meaning the surrounding notes.

There are two aspects to the musical context: the vertical and the horizontal. “Vertical” refers to notes played simultaneously, such as a block chord. Voicing, or how loud the individual notes of a chord are played relative to one another, is an essential aspect of playing block chords. If all the notes are played very loud, the chord can sound ugly, even for a chord marked fortissimo. At other times, even voicing is desired (sometimes also in fortissimo). Vertical balance also refers to the melody in its dynamic relation to the accompaniment. The best artists are able to play an extremely soft yet controlled pianissimo accompaniment while projecting a beautifully singing melody.

“Horizontal” refers to notes played one after the other. Inevitably this involves rhythm and timing. If a note is played at a given volume but comes too soon, it will not sound beautiful in this context. The art of musicality involves timing the note “just right” and playing it with just the right dynamic level. This is what keeps us musicians practicing for a lifetime!

We should remember that playing a musical instrument is an art rather than a science. For all of the points about the acoustics and physics of the instrument mentioned in this article, as players we shouldn’t become overly scientific. How we shape the hands does influence how we press the keys, and the choreography of the hand throughout a motive or phrase influences how we play the next notes, allowing them to sound like part of a coherent musical idea.

Ultimately, I believe that when it comes to playing with a beautiful tone, it’s important to be critical in the best sense. Most of all, this means listening to ourselves with a critical ear and developing increasing sensitivity to the sounds we produce. Technique is about control, and we should strive to control the keys at all dynamic levels, from the softest pianissimo to a ringing fortissimo.