BMW has partnered with the website Medium for a series of sponsored posts explaining how the car company’s design process works.

One article focuses on the acoustics of the door closing on the new BMW 4 Series Gran Coupe. The person at BMW responsible for perfecting the new door-closing sound profile, Florian Frank, has an actual title: “Specialist for noise, vibration and harshness.”

Click the audio player above to hear what the door sounds like before and after the acoustic engineers got their hands on it.

I couldn’t tell the difference either.