FDN Late Reverberation

• Generalized state-space model (unit delays replaced by arbitrary delays)
• Note direct path weighted by $d$
• The ``tonal correction'' filter $E(z)$ equalizes mode energy indepedent of reverberation time
  (perceptual orthogonalization)
• Gerzon 1971: ``orthogonal matrix feedback reverb''
  cross-coupled feedback comb filters (see below)
• Stautner and Puckette 1982:
  $$\mathbf{A}\mathrel{\stackrel{\mathrm{\Delta}}{=}}GQ \;=\;g\frac{1... ... 0 \\ -1 & 0 & 0 & -1\\ 1 & 0 & 0 & -1\\ 0 & 1 & -1 & 0 \end{array}\right]$$