A sonic boom is a continuous noise, not just at the transition. You perceive it as a single noise at the ground, but so does every other person along the entire flight path.
Boom's aircraft uses a modern design that reduces the loudness of the sonic boom.
Thanks for the correction, I did have that incorrect. TIL.
Interesting follow-up -- from https://en.wikipedia.org/wiki/Sonic_boom, the angle of the shockwave cone decreases (i.e. gets narrower) as the plane's velocity goes up. I'm wondering at what Mach number would the cone be tight enough that it doesn't intersect land?
Boom's aircraft uses a modern design that reduces the loudness of the sonic boom.