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Guideline for replacing a VST2 Plug-in by a VST3 Plug-in

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Here you can find some informations about how to write a VST3 version of a plug-in which already exists as VST2 version. How to guaranty that a Host will correctly replace the old VST2 by the new VST3 version of your plug-in.

For a VST3 Host the important information is the UID of your (processor) plug-in, with this information it will find the correct VST3 version to use.

2 scenarios are possible: The VST3 and the VST2 version of your plug-in have the same UID or not.

VST2 and VST3 version of your Plug-in have the same UID

It is possible to reuse for a VST3 Plug-in the same generated UID of a VST2 version (based on 4 characters + its name), this should work with most VST3 Hosts. Check the function which generates a VST3 UID from a VST2 UID here and reuse this value as UID for the VST3 plug-in (processor component UID)

VST2 and VST3 version of your Plug-in have not the same UID

For this use case since VST SDK version 3.7.5 we have 2 possibilities for a VST3 Plug-in to inform the Host about which VST2 Plug-in it could replace:

Using the moduleinfo.json file

The Compatibility json array in the moduleinfo.json allows to list the UIDs which could be replaced by the VST3 Plug-in.

Using the IPluginCompatibility interface

The plug-in should implement this interface (pluginterfaces/base/iplugincompatibility.h) when a moduleinfo.json file cannot be used (when no bundle is available for example). Check here.

Preset/Project compatibility VST2 <-> VST3

Check the FAQ here which shows how to use the helper function VST3::tryVst2StateLoad and read a VST2 state into a VST3 Plug-in.

It is possible to write back for VST2 backward compatibility by using the helper function VST3::writeVst2State (public.sdk/source/vst/utility/vst2persistence.h).

Parameters compatibility

VST2 was using index to identify parameter, VST3 uses an ID. It means that to be compatible the VST3 parameter ID should be kept to same index value as the VST2 one (starting from 0).

If the parameter range or behavior is not changed, previously parameter automation in host should be played back correctly.

If you change the meaning of a parameter (range, conversion normalized to plain value), it is recommanded to create a new ID for this parameter.

You could add in the VST3 Plug-in a structure to your parameters by using Unit.