Just purchased Synthesia to practice sight reading random chords. The Sheet Music functionality isn't working quite as advertised. Here's a randomly generated set of chords (attached):
Here's how it shows up in Synthesia:
Diatonic repeats ("A and Ab") are used instead of the enharmonic equivalents ("A and G#"). This causes notes to appear on the same spaces and also an overlapping sharp (or flat) and natural. Something like https://web.mit.edu/music21/doc/moduleR ... nharmonics could be used to find a better way to display these chords.
All black keys are written as a flatted note except for F#/Gb which is always F#.
Even non-overlapping diatonic notes that are close together have their accidentals overlapping each other instead of spaced apart.
The situation those random chords has produced is called "accidental stacking" and it is an interesting problem.
Synthesia will be switching to the Lomse sheet music renderer (for MusicXML files) in the next update. This is the same rendering backend used by LenMus. So if that app is able to handle your files better, Synthesia will be able to, too.
For what it's worth, I only got Lomse on the task list at the end of last year (and have been dealing with some of Google's imposed Android hassles since then), so the chart is probably an over-estimate at this point. I expect the slope to change fairly dramatically soon.