Density is how much mass is present in a given unit of volume. Things that are more dense generally are thicker, more solid objects that do not allow as much for individual particle vibration. That is one of the physical characteristics that make them solids, their particles are tightly locked into a lattice-work arrangement. The vibrations they would produce would typically be shorter wavelength vibrations, which would tend to produce higher-pitched sounds. The relationship between density and pitch produced may be easily demonstrated using a ruler, either wooden or plastic, against a rigid desktop edge. Hold the ruler on the desk with the first two inches on the desk, "snap" or "twang" the other ten inches sticking out away from the desk. Notice the sound it makes. Try it again, but move the part you are holding against the desk in by one more inch, making it three inches. When you twang the ruler again, you will notice the sound it makes is significantly higher than the first one you produced.