The EMPP project outfits a traditional piano with electromagnets mounted in close proximity to its strings. The electromagnets are controlled via audio signal from a software synthesizer (or forseeably any other audio source) –

As with other piano preparations, the range of sounds available to the pianist in some ways resemble the sound of the unprepared piano e forte, and in other ways is quite divergent. For example, by sending a sine wave signal from a computer to the A4 string (440 Hz), the string will vibrate at this naturally resonant frequency. A sustained tone will eminate as long as the electrical signal endures, and will be shaped by the contours of the piano string and body, in a manner analogous to filtering. What is especially exciting about this method of vibrating the string is the ability to send virtually any sound wave into a string. In the previous example, one could send another sine wave into the same A4 string, but at a frequency of 880 Hz. The resultant tone will then be an octave higher than that heard from pressing the A4 piano key normally. Having the option to isolate partials on each string and combine them in different ways opens up new pathways to timbral expression previously available to the pianist in some degree, but typically regarded as a synthesis method of the electronic musician.

As you might expect, the resulting voice of the instrument covers quite a range – but always with a certain piano-sustain characteristic. I imagine hearing these sounds firsthand would be all the more interesting. [via Experimentalist Anonymous]