Midi keyboard key count

Question

I was looking at some midi keyboards, I already have an Akai MPK Mini MKII

It's a 2 octave keyboard but It has an extra key off the right side C,D,E,F,G,A,B | C,D,E,F,G,A,B | C

Here's it in an image:

What's the purpose of that extra C key? Couldn't they have removed it to make the dimensions smaller?

While there are keyboards like this M-Audio Keystation Mini: It has two octave of keys without the extra key. Are these just design decisions?

Would there be any benefits/drawbacks to having that extra key as in the Akai device?

Answer 1

Looking closely, the M-Audio device actually have 8 extra keys (on top of the two octaves). I think adding extra keys at the top always improves usability. Since I mostly play in C, I use the extra key at the top quite often; I think it's a practical consideration.

Answer 2

Modern electronic keyboard instruments smaller than 88 keys mostly come in N octaves + 1 key sizes: 25-, 37-, 49-, or 61- key; they're more or less industry standards. These are also referred to as 2-octave, 3-octave, 4-octave, and 5-octave after the largest interval that can be played on them. The M-Audio mini-32 is a bit of an oddball.

There's no compelling reason for this structure other than allowing stacked octave intervals to make use of the whole keyboard. This mostly favors the key of C, but since most synthesizers have some sort of transposition facility, if you absolutely need to play a 2-octave G-G interval on the Akai MPK Mini MKII, you can arrange it.