Of course, digital piano makers have put more effort into copying the tone of the acoustic piano than any other aspect. How they've done this is beyond the scope of this article (see "Digital Piano Basics" for this information), but one interesting attempt is that of adding a soundboard to the digital. The Kawai CA-91, introduced in 2006, with its Soundboard Speaker System; and the Yamaha CGP-1000 Clavinova in 2007, with its Hybrid Active Soundboard System, both use an actual piano soundboard, set in motion by transducers, to augment the conventional speakers and impart a more natural tone to the instrument.
The latest entry in the hybrid arena is also the first instrument to formally appropriate the title of Hybrid Piano. Yamaha unveiled its AvantGrand N3 at the 2009 music industry (NAMM) trade show in January, and its vertical cousin, the N2, a few months later. The AvantGrand elevates the digital piano to a new level with a number of hybrid technologies. First among them is the use of a grand piano action. As mentioned above, this eliminates any discussion of whether or not it feels like an acoustic piano action — it is one. (However, whether the action feels right is still a legitimate topic of discussion.) This action controls the digital voices through the use of optical sensors, which measure the velocity of the keys and hammers without actually contacting any part of the action. It's important to note that this same grand piano action is employed in the vertical model N2, eliminating the second-class citizenship of the vertical piano.
(This brings up the interesting observation that, with digital pianos, there is absolutely no meaningful distinction between "grand" and "vertical" pianos. In an acoustic piano, the principal difference between grands and verticals is that in a grand, the cast-iron plate, strings, and supporting wooden structure lie horizontally, whereas in a vertical they stand vertically. The actions are arranged differently to accommodate the different structures. But because there are no such structural parts in a digital piano, and the actions are the same, any perceived differences are in name and furniture styling only.)
One element of the traditional acoustic vs. digital argument that changes with the presence of a real action is the digital's advantage of rarely needing maintenance. While the AvantGrand will never need to be tuned, eventually its action will require some degree of adjustment or regulation. (We'll bet the piano technician will be in for a surprise when, on arriving to regulate the action, he or she finds the "piano" is a digital.)
But there's more to the feel of an acoustic piano than its action, and this brings us to the last of the acoustic piano attributes that digital piano makers attempt to copy: the intangibles. In this case, the "intangible" is actually tangible — the vibration generated by the strings and transmitted throughout the instrument. Yamaha has added this ingredient by connecting transducers to the action to send the appropriate frequency and degree of vibration to the player's fingers when playing. This is where the experience of playing the AvantGrand becomes a bit ... spooky. Not unlike the experience of amusement-park rides that convince your brain that you're dodging asteroids while hurtling through space when you are, in fact, fairly stationary, the AvantGrand's Tactile Response System quickly convinces you that you're feeling the vibrations of strings that aren't actually there.