But as you reduce the speed that the drive shaft is rotating, you lower the frequency of the sound it’s making. There comes a lower limit where the engine is making what Gordon calls “groan-y and moan-y” noises which people find unpleasant. The car sounds broken. So cars had to keep the engine’s RPM above a certain level, hurting their fuel efficiency, or risk alienating customers.

GM’s solution was to implement active noise cancellation, the same technique used in some headphones to quiet ambient noise. Microphones in the body listen to the ambient sounds the car and engine are making, and the car plays the opposite of that over the vehicle’s speakers. The sound waves from the engine are cancelled out by the sound from the entertainment system, netting a quieter ride that can be more fuel efficient without being so bothersome.