Fade-In Control for Feedback Delay Networks

In virtual acoustics, it is common to simulate the early part of a Room Impulse Response using approaches from geometrical acous-tics and the late part using Feedback Delay Networks (FDNs). In order to transition from the early to the late part, it is useful to slowly fade-in the FDN response. We propose two methods to con-trol the fade-in, one based on double decays and the other based on modal beating. We use modal analysis to explain the two con-cepts for incorporating this fade-in behaviour entirely within the IIR structure of a multiple input multiple output FDN. We present design equations, which allow for placing the fade-in time at an arbitrary point within its derived limit.