Roles of the PresetBank

Preset is an aggregate (preset name + N x normalized parameters)

PresetBank is an aggregate (M x Presets + "current" index)

PresetBank and Preset fulfills many different roles that we need to analyze.

What different modules need from Presets and the PresetBank:

(this is the current state of Dplug as of Jan 2021)

dplug.client.client.Client

• holds factory presets
• gives access to the PresetBank as a part of itself
• can create a default Preset

LV2 Client:

• doesn't need the presetbank to save/restore, the host deals with that with parameters
• ergo, upgrading chunks would not allow state without using the LV2 extension for this
• generating the LV2 presets iterate the PresetBank and hence keep the normalization to make the .ttl

VST3 Client:

• save/restore with state chunks from the presetbank (but state chunks have nothing to do with the presetbank actually)
• can get preset names (but not set them)
• expose a fake program change parameter, which is used by the host to change the preset (again: normalized)
• setting this parameter calls _presetBank.loadPresetFromHost, which does the following:
  • calls putCurrentStateInCurrentPreset which store current state into current preset (!!?)
  • calls loadFromHost which put the nth preset values into the parameters

AAX Client:

• save/restore with state chunks from the presetbank
• generating the AAX presets iterate the PresetBank and hence keep the normalization to make the .tfx, where the state chunk is wrapped.

AU Client:

• save/restore with state chunks from the presetbank, wrapped inside
• can get the current Preset values and name
• can set presets, calling loadPresetFromHost
• can appends a new default preset and load immediately, using addNewDefaultPresetFromHost (!!?)
• current index doesn't seem to be used?
• describing factory presets (kAudioUnitProperty_FactoryPresets) needs a lot of CoreFoundation scaffolding

VST2 Client:

• save/restore with host-provided mechanism, we'd like to go into chunks instead
• can set and get the current preset index. Setting is done with: loadPresetFromHost
• can get and set preset name
• effGetChunk returns "preset" and "bank" chunks: one contain just the preset and the other contains the whole bank. They are only used in VST2.4 when chunks are activated.