Interesting, never really thought about humidity changing sound. Usually do it for comfort, static reasons.
Here in the PNW, we have had a colder winter, humidity has dropped into the 20%, my skin hates it, my plants hate it, my TT really hates it. Been running my humidifier 12+ hours a day on high. Got the humidity around 45% now. Can't say I notice a sound difference. But I have thinking "my system sounds really good" lately.