Extending The Effects Engine Report W13

Hello,

During this week I worked on adding two new features to LV2 support branch. One of them was displaying why an LV2 plugin is not available, more specifically, why the button for a specific plugin is disabled inside LV2 Preferences. In order to do this, I did some refactoring inside LV2Backend class. Previously, only the valid LV2 plugins were added to LV2Backend::m_registeredEffects and getEffectIds() returned m_registeredEffects.keys().toSet(). Information about all the discovered plugins was stored in a separate list which was built inside enumeratePlugins(). The major flaw with this desing was that information about plugins which were not valid could be stored only when the list was built. I solved this issue by adding all the discovered plugins to LV2Backend::m_registeredEffects, even if they were not valid. This way, we have access to a plugin's EffectManifest and LV2Manifest from the backend regardless if the plugin is valid or not. getEffectIds() method was modified to return only the valid LV2 Effects, because effect instantiation is based on it. Another method which returns all the discovered plugins' IDs was used inside LV2 Preferences. LV2Manifest was modified too, it now features a new private Status field which is set upon manifest's construction. Status is an enum with the following options:

• AVAILABLE --> the plugin is valid
• IO_NOT_STEREO --> the plugin is not valid because input and output samples are not in stereo format
• HAS_REQUIRED_FEATURES --> the plugin is not valid becuase it requires some features we are not currently supported

Inside dlgpreflv2.cpp I cycled through the discovered LV2 plugins, extracted the LV2Manfiest and set a tooltip for plugins which were not valid based on their Status.

A nice small addition was using the LV2 logo as an icon for LV2 Preferences.

The second feature I added was remembering the selected parameters and button paramters for each LV2 plugin across Mixxx's lifetime. Before this feature, every time we wanted to modify the displayed parameters for an effect we had to do it from scratch, because all check boxes were empty. This was an issue because the menu was misleading the user into thinking that no parameters were displayed for that effect. In fact, the first 8 parameters and button parameters were active. Now everything works as expected:

• if an effect's settings were not modified, the first 8 parameters and button parameters are checked;
• if the user modifies an effect's settings: the next time he will attempt to modify the same effect's settings, the previously selected paramters are checked.

I also worked together with Daniel on improving the Graphic EQ Effect. We had some problems because the equalizer was not flat and bit perfect when the filters were in neutral position. Thanks to Daniel who found the "magic" center frequencies for the filters, the effect seems to be working as it should. If we decide the equalizer based on these filters (low shelving, high shelving, peaking biquad) is good, we can easily create a 3 band or a 20 band version of it.

I polished the EQ Rack branch by removing debug comments across the code and making it ready for merging (fixed conflicts with master). These are the ideas behind the EQ Rack:

• another EffectRack is added which dynamically gets populated with EffectChains, each time the control responsible for the number of decks is changed
• each EffectChain contains only one EffectSlot, is set to fully wet and is active on a specific [Channel];
• inside Equalizer Preferences we can choose which EQ Effect should be active on each Deck
• skins don't need to be modified because aliases are created dynamically when the number of decks is changed
• example: "[ChannelX],filterLow" is an alias for "[EffectRackY_EffectUnitX_Effect1],parameter1", where Y is the index of the last Effect Rack (the EQ Rack)
• the "Bypass" check box is equivalent to loading an empty effect on the EQ Effect spot for each Deck
• a nice feature is offering the advanced user the possibility to load any available effect on the EQ Effect spot; this is done via a "Show all effects" check box
• EngineFilterBlock is no longer used because all sound processing is done by the EngineEffectsManager

LV2 support summary:

• can run LV2 effects which are using stereo input / output audio samples and don't require any features (examples: kn0ck0ut, Calf Phaser, Calf Flanger, SWH karaoke, etc.)
• pop up menu display of available options for enumeration parameters
• LV2 preferences menu
• displays the discovered LV2 plugins
• displays the reason why a plugin is disabled
• lets the user select up to 8 parameters and button parameters to be displayed inside the skin

Google Summer of Code has come to an end. It was a great experience for me and if I were to choose I'd do it all over again. I've learned a lot of new useful things, including both the technical and the soft skills required for working on an open source project. I am highly indebted to my mentor Daniel for constantly watching my back and giving precious advice to me. I also want to thank the entire Mixxx community for supporting me. I will continue contributing to Mixxx because a lot of fun new stuff lies ahead. Thank you!

Yours sincerely,
Nicu Badescu

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