Quote:
Originally Posted by Casey  The modal density question is a good one. Knowing what defines it in an artificial reverb is the first step to knowing how to control it.
The modal density is the superposition of the frequency response of all of the feedback and feedforward paths in the recirculation part of the topology, excluding the ones within any allpasses. |
I presume that you are referring to the delays within input or output diffusion allpasses, and not the delays within allpasses embedded within the recursive part of the reverb.
I was thinking about modal density versus the "size" parameter. In most reverbs I have seen, increasing size by a factor of 2 simply scales the delays by a factor of 2. This maps size to the length of the longest delay in the room, or how long it takes for an input signal to bounce back.
In a real acoustic space, increasing the room sizes by a factor of 2 will increase the volume by a factor of 8; in other words, the volume increases as the square of the size increase. However, the Schoeder frequency is calculated as 2000*sqrt(RT60/volume), so the Schroeder frequency maps more linearly to the size parameter - as the size is increased by 2, the Schroeder frequency is decreased by 2.
Reverberators based around digital delay lines have a resonance density that is constant across all frequencies, versus real acoustic spaces where the density increases with the square of frequency. In a digital reverberator, the average modal density will vary linearly with frequency, and the Schroeder frequency will vary as the inverse of the size decrease. So it seems like mapping the size parameter linearly to the increase in the delay line lengths seems like a good idea, at least from a perceptual perspective.
Sean