Simplifying the Secrets of Upright Aftertouch

By Hannah Beckett

Aftertouch is an elusive concept. It is hard to define because there are so many different factors at play, and solving the formula isn’t as simple as applying a set of numbers (or factory specs) and getting a predictable result. This article is a fresh approach to understanding aftertouch. If you’ve been confused by this concept, try to throw out what you have been taught so far and read like a novice.

Let’s start at the beginning. The piano was a revolutionary instrument because of repetition, or its ability to repeat a note very quickly. It is one of the fundamental components of the instrument: the better the piano, the faster the repetition. The more notes a pianist can play, the higher the threshold of virtuosity.

While all parts of the action play some role in repetition, the jack is the most critical piece of the puzzle. Think of the jack as the middleman between the pianist playing the key and the hammer activating the strings. Since the jack is the most important, let’s focus on the measurements that have the greatest impact on how the jack behaves: key dip and hammer blow distance. Getting this relationship correct will unlock all the repetition potential that a piano has.

Thankfully, we have a range of specs that are fairly standard across all makes of uprights. Your ability to select the correct measurements for a particular piano from the range of acceptable options will depend on your understanding of correct jack function.

Let’s start with the numbers for key dip and hammer blow.

Keep in mind that while you’re experimenting with this first set of specs, letoff and checking should be regulated well enough that they will not interfere with the keystroke. You’ll also need to adjust the capstan for lost motion after every change you make. Read the lost motion article here for more guidance.

Key dip is typically set between 9.5mm - 10.5mm, and hammer blow distance is set between 44.4mm - 47.6mm. There may be times when you must go a little wide or narrow of these measurements. Very short consoles or poorly designed pianos require a little more compromise than what is required of a quality piano. In general, you should be able to get most pianos to work within these ranges.

Let’s set key dip at 10mm, and hammer blow distance at 47mm. On this particular action model, these specs result in no escapement of the jack from under the hammer heel:

Notice that there is no visual space between the jack and the hammer heel, and you may also observe that the hammer bobbles a bit on a regular key stroke. This action is telling you that you need to either increase key dip, or decrease blow distance to allow for more escapement between the jack and the hammer heel.

Let’s set key dip at 10.5 without changing blow distance and see what happens:

The jack has somewhat more space, but it is still not enough to allow the jack to escape from under the hammer heel.

Now let’s change blow distance to 45mm. (If you’re actually doing this, remember to adjust lost motion!)

There is now visible space between the jack and the hammer heel because the jack is able to escape fully from under the hammer.

This escapement of the jack from under the hammer heel is what we call aftertouch.

Too much aftertouch means that you have excessive escapement of the jack from the hammer heel. This reduces control and creates a loss of energy.

Too little aftertouch means there is no escapement of the jack from the hammer heel, and the results are loss of control, bobbling hammers, poor repetition, and much more.

Since the key conveys information about how the jack and the hammer heel are interacting, pianists develop a sense for aftertouch. Aftertouch acts as a bit of a shock absorber for pianists by providing a cushion of space between activating the action and landing on the front rail punching. When it is correct, they feel a sense of ease under their fingers.

To feel aftertouch, slowly depress the key until the hammer reaches letoff. Pause, and then continue to press the key until the front rail punching is slightly compressed. The space the key travels between letoff and the front rail punching should be about 1.5-2mm. This is a hard distance to gauge by touch, but pianists will describe a lack of aftertouch as “shallow,” or they may say, “the key is bottoming out,” or the piano will feel very hard at the bottom of the key stroke. If you practice feeling for that small cushion of space on pianos you have regulated correctly, you will develop a familiarity for the feeling of healthy aftertouch. Do this test on every piano you meet, and you will certainly start to feel differences from piano to piano. In time, you’ll be able to assess the health of a piano by the amount of aftertouch you feel.