Symbolism, Imagery, Allegory
In Record Four, I-330 comes out and plays a Royal Grand piano. The State intends it to be an example of how wild and uncouth the ancients were:
They were able to compose only by bringing themselves to attacks of inspiration, an extinct form of epilepsy. Here you have an amusing illustration of their achievements. (4.6)
Unlike the State's music, the piano's is "senseless disorderly crackling" (4.11), but it has the power to speak to people's real humanity. Its wildness is both desirable and repugnant to D-503, who finds it fascinating despite his wishes otherwise.
The piano thus becomes a symbol of humanity's real emotions: the passion, the chaos and the wildness that comes with freedom. (Small wonder I-330 is playing it; she's as much a representation of those things as it is.) The State's relationship to it is a lot more ambivalent. It wants to show everyone how bad and wrong and icky it all is: the sort of wild and chaotic "creativity" that the State wants to wipe out forever, ostensibly for the good of all.
Yet the very fact that they have to schedule a lecture around that subject shows that they need to keep acknowledging that the piano once existed and that the music it produced once happened. It's an ironic turn, since that very music helps awaken the very feelings of creativity the State wants to stamp out. They might be better off just destroying the piano and pretending it never existed rather than pointing how much they disapprove of it. It's hard work stamping out the human spirit. The piano thus becomes a strong symbol of something that the State can't help but deal with no matter how much we might not want to.