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| WaveWarp 2.0 Component
      
Reverbs:
Functional Description
Reverberator consisting of an FIR portion to simulate the early reflections,
followed by an IIR portion to simulate the diffuse decay, according to the
design in
[Moorer2].
Algorithm
A verbatim implementation of
the reverberator illustrated in
Fig. 12 of
[Moorer2].
An FIR stage consisting of 7 or 19 taps, plus the direct signal, is
used to simulate the early reflections, accounting for the first
40 to 80 milliseconds of the room response. The resulting signal is then passed
to the IIR stage which simulates the dense build-up of late reflections
by virtue of the
recirculating delays in a parallel bank of six comb filters (with built-in
low-pass elements in their feedback paths) followed by an all-pass filter.
The output of the IIR stage is delayed such that its first echo coincides with the end of the
last echo of the FIR stage. The delayed IIR output is added to the FIR output,
with separate gain factors to weight their relative contributions, then added to
the original "dry" signal, with another gain factor to adjust the "wet/dry" mix,
before being sent to the output.
The settings of the reverberator are adjusted via the Parameter Window,
as summarised in the following table. Stereo signals have separate adjustments
for left and right
channels.
| Parameter | Purpose |
|---|
| "Reverb time" slider |
Adjusts the overall reverberation time by appropriate setting of the
comb filter gains.
From the value of this slider, denoted T (in seconds),
the quantity denoted g in
[Moorer2] (p. 18)
is given by: g = 1 - 0.366/T, according to the
approximate curve-fit in Fig. 13 of
[Moorer2].
The six delays, m, and low-pass gains, g1, of the comb filters
are interpolated
from the data listed in
Table 2 of [Moorer2],
which was obtained from a series of
optimizations
designed to match the model filter frequency reponse with measured data.
Finally, the six comb gains, g2, are obtained from the
value of g given above, and the six low-pass gains, g1, according to
the following formula
(from [Moorer2]): g2= g (1-g1).
(See also the Moorer Comb
and the Moorer Comb Bank
components for isolated implementations of a single comb filter, and of
a parallel bank of six, respectively.)
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| "Stereo separation" checkbox |
For stereo outputs, selection of this option results in a "widening" of the
stereo field by implementing different parameters for the
all-pass filters used to process the left and right channels (downstream of the comb bank).
With reference to Fig. 1a of [Moorer2],
the all-pass gain, g, and delay, m, (different from their previous use above) are set to 0.7 and 6 milliseconds, respectively, for
mono and left channels. If the "Stereo separation" is enabled, the settings for the
right channel are 0.73 and 6.5 milliseconds, respectively, otherwise, they are the same as for the
left channel.
(See also the Moorer Allpass
component for an isolated implementation
of an all-pass filter).
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| "Early reflections" selection buttons |
Selects either the 7-tap or the 19-tap early-reflection FIR filter,
as summarised in Table 3 of [Moorer2].
Note that the 19-tap version is taken from a highly-idealized geometric simulation of the
Boston Symphony Hall!
(See also the Moorer Multi-tap
component for an isolated implementation
of the FIR early reflection filter).
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| "Mix" slider |
Adjusts the relative mix of reverberant ("wet") versus original ("dry")
signal contributions at the output.
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| "Output" slider |
Adjusts the amplitude of the output signal, after the reverb has been applied.
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| "Early/late" slider |
Adjusts the relative mix of early (from the FIR stage) versus late (from the IIR stage)
signal contributions to the reverberant portion of the output mix.
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All delays in the FIR and IIR stages are implemented using circular buffers.
For more information on
room acoustics and
reverberation, see, for example:
[Roa] p. 477-492,
[Moore] p. 370-394,
[Ros]p. 459-493,
[Be] p. 172-222,
[Zo] p. 181-205,
plus various articles in
[AES8]
and
[AES16].
Signal Implementations
| Audio signals | Control signals | Description |
|---|
| Single input single output mono-mono | n/a | The entire reverb is applied to the mono audio input, and sent to the mono audio output. |
| Single input single output mono-stereo | n/a |
The FIR and comb filtering is applied to the mono audio input, then sent to
separate all-pass filters for the left and right output channels. These two all-pass
filters are identical, unless "Stereo separation" has been enabled in the Parameter Window.
| Single input single output stereo-mono | n/a |
Each audio input channel is filtered separately
through an FIR and comb bank
(but with the same filter coefficients). The filtered channels are then
sent to
separate all-pass filters for the left and right channels. These two all-pass
filters are identical, unless "Stereo separation" has been enabled in the Parameter Window.
The outputs of the all-pass filters are averaged, then sent to the mono output.
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| Single input single output stereo-stereo | n/a |
Each audio input channel is filtered separately
through an FIR and comb bank
(but with the same filter coefficients). The filtered channels are then
sent to
separate all-pass filters for the left and right channels. These two all-pass
filters are identical, unless "Stereo separation" has been enabled in the Parameter Window.
The outputs of the all-pass filters are sent to the respective stereo output channels.
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Related components:
Example DrawingBoards illustrating usage:
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