Comment by mrob

>Clarinets are keyed in Bb (you play a C, out comes a Bb), horns in F (you play a C, out comes an F), trumpets in Eb (this should be clear), and so on...

In reality, you put your fingers in the position for a C on that specific instrument and you get a C. The name "transposing instrument" is misleading; the instrument itself does not transpose. It's purely a notation convention, intended to give you a consistent mapping between notation and fingering so it's easier to switch between instruments. If you only play one instrument there's no need for it. And even if you do, it's not strictly necessary, e.g. recorders are commonly available in both C and F and are conventionally not notated transposed. Professional players routinely switch between them for different pieces.

I expect it would be possible to train an image-processing LLM to OCR sheet music so it can be automatically transposed and re-engraved for compatibility with absolute pitch.