You might be asking yourself: Why is it important to understand what “keyboard action” means? Well, to put it simply, keyboards are designed to emulate the physical mechanisms of acoustic pianos. That may seem like a straightforward objective, but the truth of the matter is a bit more complicated. While we may judge a software piano instrument for its accuracy in capturing and re-creating an authentic piano sound, “authenticity” as a metric for keyboard action is less useful. Our relationship between physical input and sound production can define the very way play one instrument compared to another! With so many options and avenues of key-based expression, it only feels proper that we clear up the confusion, define the three primary types of keyboard action, and discuss why understanding the differences between them is integral to learning and improving as a player.
- What Is Keyboard Action?
- Synth-action Keyboards
- Semi-weighted Keyboards
- Fully Weighted Keyboards
- Which Action Is Best for My Playing Style?
- Further Considerations
What Is Keyboard Action?
If you’ve ever shopped for synthesizers, digital pianos, or keyboard controllers, then you’ve likely encountered the word “action” in relation to their keys. Generally speaking, “action” describes how the keys feel as a combined result of the materials used in construction, the mechanisms used in input detection, the design of the keybed, and the overall capacity for expression. It’s also helpful to consider how an acoustic piano functions as a point of comparison; pressing a key causes a hammer to strike a string, which then resonates for a duration of time. It may seem obvious to point out, but how long you keep a key pressed directly influences how long the note resonates. This is because the hammer has yet to return to its resting position — in which its contact with the string would halt further resonance. This interval is what’s referred to as “escapement.”
Escapement seems simple enough, right? It’s the interval between pressing a key and the key returning to its original position. But think about what that means in practice. How long you keep a key pressed; how fast you transition between notes; how quickly the hammer strikes from the moment the key is pressed . . . These are just a few facets of what defines successful escapement, but none of these temporal considerations matter if the string — once struck — can’t reliably and consistently resonate undisturbed. If you sit down at an acoustic piano and begin tapping the same note repeatedly with increasing speed, then you’ll eventually notice that it’s possible to strike the key faster than the escapement interval. It’s also likely that without even noticing, the increased speed is accompanied by increased velocity with each successive hit. The interrelationship between velocity and escapement — the capacity for the string to resonate appropriately — is an integral part of what we might call a “successful” keyboard design. All of these things culminate in the three main types of keyboard action that we’ll cover below: synth-action, semi-weighted, and fully weighted keys.
Synth-action Keyboards
As the name implies, synth-action keyboards are what you’d expect to find on synthesizers. Typically, these keyboards feature a spring-loaded design over any hammer or weighting system; basically, each key feels virtually the same. Playing a synth-action keyboard can be considered more similar to playing the organ rather than an acoustic piano, which typically has a heaviness associated with the lower notes that becomes successively lighter as you reach the higher registers. A classically trained pianist might consider synth-action keys an outrageous proposition: Why in the world would you want keys that feel so different from an acoustic piano?
Firstly, most keyboard synthesizers contain a wide array of possible sounds, with deep transposition and pitch-adjustment tools that make the relationship between tone and key location almost completely obsolete. Secondly, they have a completely different relationship between sound and function. Expression happens in the form of patch-building, real-time parameter adjustments, and the use of the mod or pitch wheels. Moreover, the lightweight keys and spring-loaded design allow you to play with a uniform speed across the keybed, ditching concerns for escapement in exchange for a type of performance flexibility that would be far more cumbersome to implement on a keyboard with any acoustic-style weight.
Semi-weighted Keyboards
If you’re following the index above, then you’ll notice there’s a broad trilogy of actions we’re discussing. And like any trilogy, the proverbial middle child is always a toss-up. The “semi” prefix might seem odd, but it’s a designation of the mechanism used to simulate weight rather than a declaration of how “much,” or to what degree, the keys are weighted. Like synth-action keys, semi-weighted keys are based on a spring-loaded system. Occasionally, they’ll incorporate smaller weights to add some heft, but the springs are implemented to add resistance.
It’s important to note that this physical resistance is light or mild. This offers a degree of pushback that might feel more comfortable and familiar to those transitioning from acoustic pianos. However, this design is not meant to emulate the nuanced scale of weighting or hammer-action systems. The combination of springs and weights does yield an interesting outcome in terms of playability, though: the resistance profile of semi-weighted keys is found primarily in the escapement. This means that the keys typically depress quite quickly, while the rising action is much slower, making piano techniques like glissando and other rapid successions or repetitions less suited for this style of keyboard.
Fully Weighted Keys
Calling back to our earlier discussion of the complex interrelationships of physical mechanisms, performance considerations, and physical acoustics, it’s probably not difficult to imagine that there are many ways to go about emulating these systems and their desired outcomes. As such, fully weighted keys can be divided into two primary yet related types: hammer action and progressive hammer action.
Hammer Action
With hammer-action keys, the keybed utilizes a design that incorporates an actual hammer system, complete with sensors to detect the weight of the hammers falling back under their own weight once the key is released. Though semi-weighted keys offer a form of overall resistance that some might find preferable to the unweighted synth-action designs, hammer-action keys are a more faithful re-creation of the systems used in acoustic pianos.
Progressive Hammer Action
While the concept behind the name is easy to digest, it’s important to understand that “Progressive Hammer Action” (PHA) is a generic name for several different systems operating under the same design principle. Brands like Yamaha, Casio, or Alesis, for example, use terms like “Graded Hammer Action” or “Scaled Hammer Action,” which are — in broad strokes — proprietary names for the specifics of their PHA designs. PHA systems take the concept of hammer-action keys and add what some might consider a superior level of realism. Rather than simply using a hammer-based system to mimic the concept of an acoustic piano’s mechanical action, PHA ensures that the weight of the keys — relative to their positions along the keybed — mimics that of a real piano. That is, the lower keys are heavier, and the weight decreases as you move up to the higher keys. Acoustic pianos are like this because of the force required for the hammer to strike the strings at a uniform level of volume and resonance, with the lower strings being much thicker and longer than the higher strings.
Which Action Is Best for My Playing Style?
The simple answer is that your decision should reflect how much interest you have in emulating the feel of an acoustic piano. In reality, there are plenty of other short- and long-term considerations. For instance, those new to the keyboard would benefit from semi- or fully weighted keys, as these types would allow them to build strength without the financial or spatial commitments of an acoustic instrument. That said, if you intend to go beyond piano-style sounds, then PHA keyboards might be more limiting in that the distribution of key weight is fixed to the traditional scale.
We should also talk about the interdependent concepts of form and function. For keyboard synthesizers and MIDI controllers, the piano-roll design is just a vehicle for accessing and performing virtually any sound. Moreover, your avenues for expression are uncoupled from the physical limitations of a piano-style configuration. Sources for modulation wheels can be freely assigned, and this can be taken to virtually limitless heights if you’re using a DAW-based setup and MIDI controller. Since these are more likely to have synth-action keys, they allow you to play faster while inspiring new approaches to sound that aren’t limited to preconceived ideas of pitch, placement, and keyboard arrangement. For a comprehensive keyboard weight and feel breakdown, check out the related inSync article below.
Further Considerations
It should be noted that the design and number of sensors used, the length of the keys, and more can greatly impact playability. However, these factors are not explicitly limited to one type of keyboard action. While it can influence expressivity, the core design principles of each construction style aren’t altered.
Similarly, arguments are made on both sides regarding ideas of “authenticity” and the materials used for the keys (i.e., wood, plastic, “real”-feeling coatings, etc.). Though the transition from acoustic to electric may be easier for some, the weight of the keys will be far more influential to how well you adapt.
Companies like Expressive E are among a few who manufacture incredibly unique keyboard synthesizers that don’t conform to any of these concepts. Their standalone Osmose 49-key polyphonic synthesizer and MIDI controller offers MIDI Polyphonic Expression (MPE) to allow mimicking the vibrato-style fingerings of stringed instruments, as well as a supplementary layer in its Z-axis, offering deeper, customizable expression. Though this style of product is rare, we feel it adds an enlightening context to the ideas of how sound production and sound interface do — and more often don’t — adhere to our conventional ideas of keyboard-based performance.
Ready to Jam?
We’re confident that this wealth of knowledge will help ensure your practices, songwriting, and performances reach their full potential. If you’re looking at your first time with a keyboard, synth, or MIDI controller, or you simply want to play to a different tune, then give your Sweetwater Sales Engineer a call at (800) 222-4700; they are more than happy to help you discover the instrument best suited to your creative and compositional needs.