You’ve read that right: apparently everything sounds better in the winter, especially in more humid climates (like Virginia, USA, where we live), and here’s why:

When it gets colder, the heating unit in a building turns on or is turned on, like a furnace or a wood stove.  Because of that, the humidity in the indoors drops to a pretty low level, like fifteen to twenty-five percent relative humidity.

At a lower humidity there is higher air pressure, meaning that the molecules in the air weigh more as gravity pulls down on them.  Why do they weigh more?

They weigh more because oxygen and nitrogen molecules weigh more than water molecules (if I understand this correctly as a non-scientist), and in lower humidity there is more room for oxygen and nitrogen molecules, since the water molecules have decreased and don’t take up so much space.

So, with more molecular mass in our air, there is more mass to handle the sound waves that come from your musical instrument; therefore more of the detail of the sound waves is able to reach your ears.

I can tell!  In the humid summers around here there’s a certain muffled quality to the sounds --- not terribly muffled, but noticeable, even in an air-conditioned room.  And in the winters here things sound more clear and full.  I prefer to record and do concerts in the winter because of this.

This is not exactly an earth-shaking truth, but… it’s interesting to notice it!