It's not just a high bypass ratio that has helped. It's computational acoustics (we can predict the sound something makes based on its geometry and movement in a medium), nacelle design, materials. In supersonic flight, the most pressing issue is suppressing the sonic boom. There was a lot of work on this in the late 00's, with even Cessna rumored to be working on a quiet supersonic business jet. Various attempts - a bulging, ogival nose will increase the local density raising the local mach number leading to a weaker shock, and other thing. It was a lot of fine tuning and deep insight into transonic phenomena.