MIDI Notes and Middle C

This can be C3 or C4, or even C2 or C5. There is no defined standard or convention. The MIDI standard only says that the note number 60 is a C, it does not say of which octave.

From the Complete MIDI 1.0 Detailed Specification:

Each note is assigned a numeric value, which is transmitted with any Note-On/Off message. Middle C has a reference value of 60. This is the middle C of an 88 note piano-style keyboard though it need not be physically located in the center of a keyboard.

In practice, everybody agrees that concert pitch middle C is 261.6 Hz and that this pitch is MIDI note 60 (which follows from the General MIDI specification that MIDI note 69 is the standard A = 440Hz).
So if you play note 60 you get middle C from all MIDI synthesizers; it's not different for different manufacturers. But some manufacturers call middle C "C3" and some call it "C4" or "C5".

For example :

• C3 : Ableton, Arturia, Cubase, Elektron, Logic Pro, Max/MSP, Novation, Studio One, Waldorf, Yamaha
• C4 : ASM, Expert Sleepers, Korg, Roland, scientific pitch notation
• C5 : Doepfer, FL Studio, Sonar

Octave ranges

List of all MIDI notes

Frequencies are in equal temperament at A4 = 440 Hz.