I conduct research on automatic transcription of polyphonic music. Currently, I use MAPS dataset.
In particular, I need monophonic recordings to be used as training data and polyphonic ones to be used during test. And I need the transcription of the test recordings so as to report how well the system performs.
Do you know any publicly available database that can be used for this purpose? It can involve solo instrument as well as many instruments.
This isn't exactly what you were thinking of, but one way you could do it would be to get a lot of free midi files and render them into audio. Then, check the resulting score against the original midi. I'm not sure about the methods you are using to do this, but you could automate the entire process. For example, FluidSynth can render audio files from the command line, so you would only have to feed a midi file into your program and it would do the rest. This would be especially helpful if you are using any AI learning for this program.
I came up with an algorithm to do this years ago, and still have the theoretical documentation, though I never coded it. By today's standards it is perhaps no longer too numerically intensive. It probably will struggle with percussion instruments like piano which have a very 3D quality, but should in principle work well with wind and stringed instruments, and it is designed to sort out the instruments, as to write a full orchestral score. The idea is to import something like a .wav file, and export a midi file, which can then go into existing scoring software, or be used for re-sequencing.
Not sure if this is helpful, since your interest appears to be piano, and you appear to be looking for software, not just a conceptual algorithm. However if you are still interested, you can contact me through Fracturelab.com (my business, which has nothing to to with music, unfortunately), and I can dig it up for you.
PS: My interest was also piano, since I compose by ear, and wanted to play from an acoustic instrument to a midi file. As my study of the problem revealed that it probably wouldn't work for piano, it moved to the back burner. I guess it could be used to resurrect old symphonic recordings where the score has been lost.
