What is the proper octave value of Middle C (Piano), in MIDI representation?

Question

I am currently developing an Optical Music Manuscript Reading application in C#. For the note identifcation scenario, I have found out the need of knowing the octave values for each key.

Because of represnting thie note as in example: 4C4 where (Duration)(Note)(Octave) is the order of represntation.

(Considering the Treble Clef only)

In which octave is middle C, in MIDI notation?

In which octave is the C in the below image is?

Answer 1

It's usually C3, but as Codeguy007 noted, it can vary from software to software. In my experience C3 is the most common value for middle C.

Answer 2

When working with MIDI, 440 A should always be MIDI note number 69.

What the notes are named in terms of octaves isn't as important as the note numbers.

Answer 3

C4 is by far the most widely used designation for middle C. The MIDI specification refers to middle C as MIDI note 60, and does not use the octave notation. Notably, Yamaha went with the C3 notation for their keyboards (including for their hugely successful DX7, an early MIDI keyboard), which makes some sense in that the lowest C on a piano would correspond to C0. Rival Roland went with C4, where the lowest C on piano is C1. But note that there are two more possible C notes, MIDI note value 0 being the lowest. For Yamaha that would be C-2, for Roland C-1. So it makes sense that someone would note middle C as C5, so that the lowest note is C0, so that the octave index starts at 0, particularly convenient for software. (This was done by at least one sequencer software maker.)

But again, C4 has proved the most popular. In fact its use goes back centuries, and in wide use the past hundred years. It's used in scientific pitch notation (also known as American standard pitch notation, and international pitch notation).