Transposition
The presence of the transposition function in the keyboard — switching the sound to a different key. When transposing, the pitch of all keys is simultaneously raised or lowered by a certain number of semitones. This function is useful in all cases when a melody learned in one key needs to be played in a different key — for example, if the original melody is too high or too low for the vocalist, if the external accompaniment differs in key, if you need to switch between keys during the song, and etc. In such situations, by transposing the sound, you can play a melody in a new key using the same familiar keys without relearning it.
Arpeggiator
The presence of an
arpeggiator in the keyboard.
The name of this function comes from "arpeggio" — a technique for playing chords, in which notes are not played all at once, but in turn. Accordingly, the arpeggiator is a function that allows you to play a taken chord in the arpeggio technique: the musician presses all the keys at once, and the keyboard plays them in turn. This effect can also be achieved manually, but in some cases the arpeggiator turns out to be more convenient: it plays notes at a clearly defined speed and interval, can accompany them with various effects, and provides other additional features. These features vary depending on the model, but some instruments allow you to create entire songs with the arpeggiator by simply pressing a sequence of chords.
MIDI out
A specialized output for transmitting MIDI signals to an external device — a sequencer, a computer sound card (if there is a MIDI In input), etc.
MIDI signals are a kind of "digital notation": they tell which key was pressed, with what force and for how long, and also carry information about various additional parameters: timbre, tempo, key, etc. To convert such signals a "ready" sound requires an external sequencer (software or hardware).
Note that despite its specialized purpose, the
MIDI Out output is not mandatory for modern MIDI keyboards: MIDI signals can also be transmitted via other interfaces, such as USB or Bluetooth (see the relevant paragraphs). So it makes sense to specifically look for a keyboard with such a connector if you plan to connect it to equipment with a MIDI In input.
