The sound heard on the ground as a “sonic boom” is the sudden onset and release of pressure after the buildup by the shock wave or “peak overpressure.”
The change in pressure caused by sonic boom is only a few pounds per square foot, which is equivalent to the same pressure change experienced on an elevator as it descends two or three floors, but in a much shorter time period.
This is the magnitude of this peak overpressure which describes a sonic boom.
There are two types of sonic booms: N-waves and U-waves.
The former is generated from steady flight conditions and its pressure waves are shaped like the letter N.
These waves have a front shock to a positive peak overpressure, caused by a linear decrease in pressure until the rear shock returns to ambient pressure.
The latter U-waves are focused booms which are generated at the front and rear, shaped like the letter U.
These are created when the peak overpressure are increased compared to N-waves.