000 would also be a rest and without the pitch, how would you know for example that it's a bottom G and not a middle one? Without tempo you would need a set of messages for rest durations too. Then there is alternative fingering to consider. I suspect it is doable but the user interface would have to me more complex than the one we have today ie. 3 things to press (or not in the case of a rest!). I work for a major IOT/Data solutions company and this is beggining to sound like a great exercise for one their regular "hackathons" so will run it past them. One of the most logical approaches would need the music you are testing against being digitised and that points to something like an addon to software like Sibelius or one of the cheaper options. Our guys have been very clever in the past using things like Raspberry Pi but they have the advantage of some of the best data analytics tools sitting behind them and I suspect any commercial solution would be both pricey and a legal minefield if you accept that pitch and tempo are an integral part of validating the input. We have a number of software engineers/programmers on tMp and would be good to hear their thoughts. Also, maybe @philipsparke can share some views on copyright issues.