The outputs themselves use a variale-delay tap, but using a separate fixed-
delay tap on the feedback helps improve the perceived "wobble" with sustained
notes. This also applies to the flanger effect.
Similar to the recent chorus and flanger changes, the modulation delay now
swings between -n to +n, where n is less than the delay length. This brings up
a slight issue with the linear interpolation, as modff doesn't produce the
correct fraction value for interpolation (it's inverted, with 0 being closer to
the next sample and 1 being closer to the base). So it's using nearest
interpolation for now.
The effects' specified delay is the average delay time, meaning the delay
offset should move between -n and +n relative to the delay, where n <= delay.
Each 4 related all-passes now share a structure with one delay line, which uses
an interleaved sample history. Also fixes some potential rounding problems for
delay lines with interleaved samples.
This seems to be more in-line with the intended behavior, to allow build-up and
overlap within the reverb decay, rather than a pitch-shift on input.
Unfortunately there's no readily available implementation of this reverb model
that includes modulation to compare with, so a low depth coefficient is used to
keep it very subtle.
This update modifies the reverb in numerous ways. The 3-series, 4-parallel
all-pass is replaced with a Gerzon vector all-pass. The vector all-pass is also
applied to the early reflections, to help with the initial diffusion in the
late reverb. The late reverb filter and feedback attenuation has been replaced
with a dual first-order equalization filter, which controls the low and high
frequencies with individual low-pass/high-shelf and high-pass/low-shelf filters
with gain control.
Additionally, delay lines now have the ability to blend the output between two
offsets, to help smooth out the transition for when the delay changes (without
such, it could result in undesirable clicks and pops).
This attempts to improve the smoothness of the late reverb decay by passing
each line through multiple all-pass filters. Some work is still needed to work
better in high-density and not-so-high-diffusion environments.
This also removes the decay from the early reflections, since it's no longer
continuous feedback.
