In a manual car, when you up shift, you need to wait for the engine RPM to drop to a certain value so that the engine speed matches with the speed of the gears you want to shift into. On my manual car, it can take even half a second for it to drop to a suitable RPM. If you don't wait for it to drop then you either strain your clutch or upset the engine and the car judders before the engine speed matches that of the transmission, especially in lower gears (1st to 2nd, 2nd to 3rd).
How do automatic cars, especially those equipped with double clutch double shaft trannies, manage to drop the engine RPM so fast to allow for smooth acceleration when up shifting?
I searched online but couldn't find anything. Is it because of a lighter flywheel, more gears and smaller difference in gear ratios between them, do they employ some sort of braking mechanism to actively force the engine rpm to an appropriate value?