3. Basic Types
For most musicians, the two most important considerations when choosing a master keyboard are action and range:
Unlike an acoustic piano or other mechanical keyboard instrument, the physical construction of a controller keyboard does not have a direct effect on sound production. It is possible to generate MIDI data in dozens of ways, and this data can then be used to trigger any synthesised or sampled sound, from accordion to zither. And once recorded into a sequencer, MIDI data may be edited and modified almost infinitely.
Ever since the invention of the synthesizer, most electronic keyboards have used a spring-loaded action very different from the hammer action of an acoustic piano. Some mechanism is required for returning the key to its rest position after each note is played - a spring provides the simplest possible solution.
Early synthesizers could produce many weird and wonderful sounds, but nothing sounding remotely like a piano. Only with the advent of more sophisticated tone generation, and sampling in particular, did it become apparent that playing a piano sound using a spring-action keyboard places limitations on the realism of the performance. Simply put, it is difficult to play a piano part well if the keyboard does not feel like that of a piano.
There are several differences that contribute to the unique feel of a piano keyboard. Many controller keyboards use some or all of these physical features in order to replicate their action. Since these terms are often confused, lets take a look at them separately:
While synth keys are made of light moulded plastic, piano keys are made of solid hardwood. Weighted controller keyboards usually simply add weight to the keys in order to replicate this aspect of the piano keyboard. While this is important, the weight of the keys is probably not the most important aspect of piano keyboard construction - when weighted keys are coupled to the spring action of an electronic keyboard, the result can feel rather odd. This hybrid design often uses only small metal weights, rather than fully weighted keys, to balance the force of the spring, and is usually described as semi-weighted.
The main reason a piano feels different from a synth is that its sleek exterior hides a complex mechanism, by which striking a key propels a felt-covered hammer towards the string while simultaneously removing a felt damper. The hammer immediately springs back, while the damper returns to stop the string from sounding only when the key is released. Hammer-action controller keyboards usually dispense with some of the complexity of this mechanism, while retaining the central feature the hammers! Hammer-action keys feel different from springy synth keyboards because the hammer takes time to move, time to return to its rest position, and imparts force back to the key when it does so.
The most advanced type of hammer-action design is known as a graded hammer action. This goes even further in imitating the feel of an acoustic piano by gradually increasing the weight of the hammer mechanism (and thus the force required to play each note) from the highest notes (lightest) to the lowest notes (heaviest).
Pros and Cons
It is generally safe to assume that if a keyboard is not specifically described as weighted and/or hammer-action then the mechanism will be the simple spring-loaded synth type. These are cheaper to produce but not necessarily inferior - just as playing a piano sound can feel strange on a synth keyboard, synth sounds can feel strange on a piano keyboard. Drum and percussion sounds in particular are often easiest to play on a light synth-style keyboard - try playing an intricate hi-hat pattern on hammer-action keys, and this will quickly become apparent!
This is possibly the simplest defining feature of any keyboard - how many keys does it have? Range is usually defined by the number of keys (both black and white) rather than the number of octaves. The commonest sizes in production are 88 (full piano range), 76, 61, 49 and 36. Keyboards as small as one octave (13 keys inclusive) do exist and can be very useful for their portability, although by definition they are more suited to playing basslines and entering notes into notation software than playing full keyboard parts.
Generally speaking, the larger its range, the more likely a keyboard is to have weighted keys and a hammer action. A one-octave weighted keyboard would be a rather redundant creation, and while 76-note synth-style keyboards are not completely unheard-of, they tend to be at least semi-weighted. Almost all 88-note keyboards have fully weighted keys.