During your search for the perfect keyboard or digital piano you'll see and hear many technical terms which sound may sound confusing or impressive, but what do they actually mean?
Polyphony - This is how many notes can be played at the same time. This appears in exponential multiples of 32 (64, 128, 256 etc) However, it's not as simple as "64 note polyphony = 64 notes at the same time" - on many modern digital pianos, the sound is stereo sampled. This means that each note uses 2 different polyphonies - effectively halving the polyphony of the instrument (So 64 becomes 32, 128 becomes 64 and so on). On pianos with a low level of polyphony players will notice when sustaining many notes or playing more advanced pieces that notes may 'drop out' while playing - for example, on a 64 note polyphony piano like Yamaha's YDP-141, if the player sustained a 33 note phrase the first note would be sacrificed for the 33rd, the second for the 34th and so on until the pedal is released.
Stereo Sampled - This refers to how the different sounds are recorded. Almost all makes and models come with a stereo sampled grand piano sound, though some are now introducing the technique on other sounds such as strings and harpsicords.
Touch Sensitive Keys - This function is found on many keyboards - it replicates the action of a piano by producing a harsher, louder sound when the keys are struck hard and a softer, more mellow sound when played softly. This can usually be turned off if using the organ or harpsicord sounds for example where the instrument remains at a constant volume regardless of how hard the keyboard is struck.
1/2/3/4 etc Track Recording - This is how many separate tracks you can record onto the Keyboard/Piano's inbuilt memory. On a 2 track system, for example, you can record a backing track onto the first channel and improvise over it with the second track. The more tracks you can record, the more intricate and impressive songs you can create!
Weighted Keys - This is seen on the full sized keyboards and digital pianos. These mimic the response and feel of a real piano whose keys are weighted down by the hammer mechanism in the cabinet which strikes the strings artificially. As with real pianos, the different brands and products all have their own nuances and feel to the action. If you're unsure, it's best to try it first!
Graded Hammer Action (GHA) Keyboard - These are like the weighted keys but go a step closer in terms of realism - with a graded hammer action keyboard, the bass notes are slightly heavier than the top notes in the treble, just like on a real piano. This is usually only seen on the more expensive pianos.
Pedalboards - These come as optional extras on some of the stage pianos such as the Yamaha P series. As most of these keyboards are only supplied with a sustain pedal, this gives you the option of expanding the pedalboard to include the regular 3 (Una Corda, Sostenuto and Sustain) rather than just a single sustain pedal which helps make it play more realistically.
MIDI or USB - These are connecting ports for use with a laptop computer, other MIDI keyboards or other compatible technology. These ports allow you to record directly from the keyboard or piano and sample or layer the sound using software on the laptop, or in MIDI's case use it for much more besides.
"Voices" and "Styles" - These refer to different sounds on the keyboard or piano. A "Voice" is simply the instrument - so the piano sound is the default "voice" on all keyboards or pianos when switched on. A "Style" is a backing track - many keyboards offer hundreds to choose from based on rhythms and musical traditions from around the world for you to play along with.
Transpose - This function allows you to change the pitch of the notes on the keyboard. This is quite handy if working with vocalists who find the key the song you're playing too low or too high, as you still play the music as it's written but the produced key will be lower or higher as you set it. It's also useful if playing, for example, the harpsicord or chamber organ sounds in an ensemble playing at Baroque pitch, which is half a step down by todays standards.
Split, Dual and other functions - These are found on most pianos and keyboards and allow for greater versatility in playing. The Split function literally 'splits' the keyboard at a set point (this can often be changed manually to suit) and allows the left hand to play a different instrument - for example, a bass guitar - while the right hand continues to play the set voice. Dual voicing allows two voices to be layered and played together at the same time - for example, Piano and Strings is a popular choice. Dual voicing allows for a lot of experimentation!
Full Sized and Organ Sized Keys - This refers to the width and overall size of the individual keys on a keyboard or piano. On any piano and keyboard where stated, the keys will be full sized, as with a real piano. Many of the smaller keyboards have 'organ' style keys which are slightly smaller.