Digital pianos are electronic devices, and there are a few technical aspects to consider when choosing your instrument:
This term describes the number of notes that can sound simultaneously. Like computers, electronic instruments are limited by the capabilities of the chips inside them, and the more sound you want to make, the more data the processor has to handle. Your piano will likely be described as having 32-note, 64-note or even 128-note polyphony. You might feel that you can only ever play ten notes at a time (unless you are Jerry Lee Lewis, who used his feet to play as well!), but remember that in the electronic world, a sustained note counts as a note even after you've hit it. Greater polyphony allows the digital piano to ring and sustain like a real piano. Watch out for models that use stereo samples - the quoted polyphony may need to be halved in reality as two 'voices' are taken up for each note played.
The Musical Instrument Digital Interface (MIDI) is dealt with in more depth in our Portable Keyboards Online Advisor. It is a system that allows you to connect two or more electronic musical instruments together and control them from a single keyboard or a computer. Many digital pianos have MIDI connections, which are useful if you are working with more than one keyboard, want to use sequencing or scoring software on a computer, or download new sounds.
A technical term for a function that allows you to create an automated accompaniment to your playing. You play in a sequence of notes, and the sequencer plays it back while you play another part. For composition or home use, a sequencer can be useful and fun. Some digital pianos have built-in sequencers and drum machines so you can create complete rhythm parts for yourself - these are often referred to as 'rhythm pianos'.
Korg C-720 RW
Some might call it cheating, but most digital pianos allow you to change the key of your keyboard electronically, making it easier to play in unusual key signatures. Beware of this facility when playing live however - unless it's quick and easy to switch between tunings, you can get badly caught out, especially if you've been playing a different keyboard for a few numbers, and then return to a piano you have forgotten to retune...
Consider the way the controls are laid out when you're choosing your digital piano. Is it easy to adjust the volume and the tone while you're playing? Is it easy to switch between sounds? If there are effects and other functions built-in, is there one button per function, or even a touch-screen, or are the parameters buried in layers of menus on a tiny LCD screen? Your piano is effectively a computer, designed by electronics specialists, and they can occasionally forget that musicians are not interested in reprogramming systems! Make sure you can do what you want to do, when you want to do it.