Let-Off Simulation on Digital Pianos

A special feature of many mid-range and high-end digital pianos is the let-off simulation, which gives advanced pianists very precise control over their play.

Piano beginners will probably not even notice whether a digital piano keyboard is built with or without a let-off simulation. In fact, the mechanism – while intercepting the key travel – is not an “obstacle” that requires a great deal of effort to overcome. However, the escapement and its position allow the pianist to play finely controlled nuances, especially during quiet passages.

How does the let-off simulation work?

The word “simulation” already indicates that it replicates a detail of the action of an acoustic piano. This detail comes from the modern double-escapement repetition action, which evolved from the first double-escapement action invented by Sébastian Érard in the mid-19th century.

The double-escapement action is a complex decoupling of key and hammer. Simply put, it ensures that the hammer is ready to play immediately after a note is struck, even before the key has fully returned to its resting position. There are two ways to trigger the note:

1. The key is fully depressed. In this case, the full range of the key travel is used at once.
2. The key is not fully released and is played from a slightly depressed point.

This is also known as a repetition action.

How does the let-off simulation on digital piano work?

The let-off point is particularly noticeable when playing pianissimo and wanting to apply as little force to the hammer movement as possible. It hence allows you to strike the keys in a controlled manner. Even a short keystroke is enough to send the hammer quickly but less forcefully to the virtual string.

Let-Off Simulation, Escapement, Triple Sensor System

Product descriptions and manuals sometimes use the term escapement (action/mechanism) instead of let-off simulation or mechanism.

On a digital piano, the let-off point is created by an inconspicuous mechanical device. Here, too, you must overcome a small resistance located further down the key travel. A tripple sensor system (3 sensors), which scans the key travel, is important for transmitting the velocity values for Note On- and Note Off-action:

Action 1: The key moves completely from sensor 1 to sensor 2 – the sound is triggered, and the velocity measurement determines how forcefully the key is struck.

Action 2: The key is not released completely but stops somewhere in the key travel. Now the note is struck again (repeated), and sensor 3 transmits the data for the new velocity measurement.