This is a very common misconception. The shooter is never directly exposed to the supersonic flight noise. The sonic crack only begins to be generated a few yards downrange and it travels perpendicular to the flight path (like the wake from a motorboat) so the shooter never directly hears it. We do hear the sonic crack reflected off hard opjects downrange, but that effect is delayed and at a lower dB level due to the distance the noise has to travel to reach the shooter's ear.
My bet on the reason the patch seems to create a higher pitched crack is that it reduces blow by, which shortens the length of the muzzle blast event. Even a few microseconds of extra time on the release of the gas will produce a lower frequency.
