Reverberation techniques

  • Author or source: Sean Costello
  • Created: 2002-02-10 20:00:11
* Parallel comb filters, followed by series allpass filters. This was the original design
by Schroeder, and was extended by Moorer. Has a VERY metallic sound for sharp transients.

* Several allpass filters in serie (also proposed by Schroeder). Also suffers from
metallic sound.

* 2nd-order comb and allpass filters (described by Moorer). Not supposed to give much of
an advantage over first order sections.

* Nested allpass filters, where an allpass filter will replace the delay line in another
allpass filter. Pioneered by Gardner. Haven't heard the results.

* Strange allpass amp delay line based structure in Jon Dattorro article (JAES). Four
allpass filters are used as an input to a cool "figure-8" feedback loop, where four
allpass reverberators are used in series with
a few delay lines. Outputs derived from various taps in structure. Supposedly based on a
Lexicon reverb design. Modulating delay lines are used in some of the allpass structures
to "spread out" the eigentones.

* Feedback Delay Networks. Pioneered by Puckette/Stautner, with Jot conducting extensive
recent research. Sound VERY good, based on initial experiments. Modulating delay lines and
feedback matrixes used to spread out eigentones.

* Waveguide-based reverbs, where the reverb structure is based upon the junction of many
waveguides. Julius Smith developed these. Recently, these have been shown to be
essentially equivalent to the feedback delay network reverbs. Also sound very nice.
Modulating delay lines and scattering values used to spread out eigentones.

* Convolution-based reverbs, where the sound to be reverbed is convolved with the impulse
response of a room, or with exponentially-decaying white noise. Supposedly the best sound,
but very computationally expensive, and not very flexible.

* FIR-based reverbs. Essentially the same as convolution. Probably not used, but shorter
FIR filters are probably used in combination with many of the above techniques, to provide
early reflections.