Comment 40 for bug 1481170

For effects that continue to produce output without any input, a pointer to the per-group enable state for the effect can be passed to the effect's process() function, which would allow the effect to turn itself off. To handle external effects like that, we'd need a preference option for the effect and ship Mixxx with a list of popular external effects that work that way so they can be shut off immediately when going into the intermediate disabling state.