Listening to various operators at different times, I've sometimes noticed, especially during contests, that some operators are easier to understand than others, and it doesn't all seem to be due to their speech patterns. The audio doesn't sound good but it's easy to understand.

At other times I've listened to two operators ragchew for longer periods of time, and while the audio is understandable, it is easier to listen to.

It seems to me that operators have a lot of control over how they sound over the air.

What makes these two sounds so different?

How do I adjust my transmitter to make these two sounds - one focused on intelligibility, and one focused on good/comfortable listening?