The actions of a digital deliver the mechanical sensation to the finger. However, the digital piano must do something with that mechanical movement to translate it into data it can use as instructions for generating sound. This is often a HIGHLY overlooked element of digital piano design, and one that most customers aren’t familiar with. Usually the limit to any discussion on this area of design is simply if they’re present at all – normally referred to as “touch sensitive” or not. However, once a customer determines if a piano is indeed “touch sensitive”, one quickly realizes that not all pianos are created equal. There are four configurations that manufacturers typically deploy, with the objective to give the widest range of accurate data points based on the velocity (pressure) of the key being played.
The majority of low-cost digital pianos and keyboards use a single sensor per key, with a very low level of accuracy, and output over the 128-point MIDI language. These barely qualify to be called touch sensitive, as most of these sensors are capable of reliably outputting 3-5 levels of velocity. When one considers that an acoustic piano has theoretically an infinite number of dynamic levels, one realizes how limiting this can be, particularly once the first 1-2 years of piano lessons are exceeded. Once the muscles develop to a point where fine motor control is honed, most well-trained young pianists can accurately play at dozens of different volume levels, and with their ear, correctly detect even more.
Better digital pianos, typically in the $2000 – 5000 range, may use multiple sensors per key to increase the level of touch sensitive accuracy and allows for a more complex tone generating algorhythm. Whereas with a single pressure-based sensor, you might get different digital outputs for the same physical input, being able to average two or three sensors increases the accuracy.
Optical sensors are newer to the market, and use Infrared technology to sense the velocity of a key rather than interpreting it’s impact pressure. These tend to be more accurate, and can be found in some of the higher-end units, typically in the $7000 + range.