Since control-ports have a fixed value for the current process-block,
Ardour splits a plugin's run() process cycle on every automation event
to facilitate sample-accurate automation.
Since automation is interpolated between events, this ensures that each
explicit automation point is reached (not interpolated).
Plugins where this is not required and which favor a fixed block-size,
can now specify an optional Feature: NoSampleAccurateControl.
One example: a convolution plugin with smoothed gain control.
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