Does anybody know why are notes written as C#4 and not as 4C#?
Do you mean in trackers like OpenMPT or in general? OpenMPT and its predecessors just copied existing conventions, i.e. scientific pitch notation (https://en.wikipedia.org/wiki/Scientific_pitch_notation) or MIDI key names, which both follow the same scheme (but what is considered to be "middle-C" differs between different notations ranging from C3 to C5), i.e. a key name followed by an octave name. Why scientific pitch notation works the way it does - I don't know, but it has been around for some centuries. Other similarly old notations like the Helmholtz pitch notation (https://en.wikipedia.org/wiki/Helmholtz_pitch_notation) follow the same pattern, but express the octaves as a set of different symbols rather than numbers.
I mean in trackers. Because hex values are written in high-nibble followed by low nibble, why not write note values as octave followed by note name?
Quote from: Ahornberg on February 13, 2023, 16:16:12I mean in trackers. Because hex values are written in high-nibble followed by low nibble, why not write note values as octave followed by note name?
Well, you could interpret the C#4 notation as actually following a high-nibble first, or big-endian, or most-significant first notation, because the note name is musically actually more important than the octave (at least in musical systems that are octave/12-semitone based).
As cryptic and efficient as tracker interfaces may be, using existing conventions that users will already be familiar with does seem like a reasonable thing to do. Even the very first trackers did it that way. Essentially you are asking why trackers didn't deviate from an existing, well-established standard - and answering why someone didn't do a non-obvious thing seems impossible to answer to me without being in that person's head.
See information from AHOY here (https://www.youtube.com/watch?v=roBkg-iPrbw&t=1473s).
While that video may be very informative, it does not answer this question at all.