acoustics - What does warming up a gong do?

This is almost something I'd cross post with the Music SE, but I specifically am looking for physics answers not music answers.

When playing a gong, one is often told to "warm up" the gong. This involves very lightly tapping the gong with the mallet a few times before striking it. The taps should be relatively inaudible.

Musicians say that doing so makes the sound "brighter," which is a very psychoacoustic term. I'm curious what might physically happen which could then be translated as "brighter" by musicians.

What changes in a gong when you lightly tap it a few times which would change the sound produced? I'd appreciate an answer which could explain any effects in terms of the soundwaves produced by the gong, but I would accept an answer which merely describes a interaction of material properties which could have an effect on the sound waves.