Couple your piano toy to your laptop by using sound interface i.e. speaker and mic.

(Alternatively you can make an AUX cable if you want to)

Write software in MATLAB that recognizes which piano key you just played (using spectrum analysis techniques) on kids piano toy or on your phone. The code will record sound using mic and then process it.

After identifying which note (e.g. C, B flat, etc) was played on the piano, automatically regenerate a pure note of the same type using very high sampling frequency in MATLAB. Play it on your computers speaker.

Can you prove that the quality of instrument has significantly improved?

Now write a similar code which will recognize what number is being dialed i.e. it identifies from DTMF tone / sound that you pressed 1 key on your cell phone dialpad / PTCL speaker phone