When recording on location, spurious environmental noises are the biggest bugbear. Fortunately, the staff of Sauder Hall were very cooperative in helping producer Erick Lichte to track down and kill noises, including the hall's air-conditioning. As you can see from the spectrum of a rough mix of a silent passage, we were still left with some very low-frequency components: these were the rumble from a distant sewage pumping station (and its harmonics), some low-level electrical noise (which appeared to come from the lights), and even more distant traffic. They are, to all intents and purposes, inaudible. In the midrange and above, the background noise is very low indeed.
For reference, the green trace is the spectrum of the noise floor of a perfect 16-bit PCM system. In theory, it looks as if 16 bits would be sufficient to capture the piano recording's dynamic range. In practice, with real-word 16-bit digital systems, listening reveals that not to be the case.