Hi,
from the FAQ in the documentation:
Q: How does Audio Processing Bypass work?
In order to implement audio process bypassing, the Plug-in can export a parameter which is additionally and exclusively flagged as having the attribute kIsBypass. When the user activates the Plug-in bypass in the host, like all parameter changes, this is sent as part of the parameter data passed to the Vst::Steinberg::IAudioProcessor::process method.
The implementation of the bypass feature is entirely the responsibility of the Plug-in:
The IAudioProcessor::process method will continue to be called. The Plug-in must take care of artifact-free switching (ramping, parallel processing or algorithm changes) and must also provide a delayed action if your Plug-in has a latency. Note: The Plug-in needs to save in its state the bypass parameter like any other parameters.
What is not clear ?
Cheers,
Arne