Extending The Effects Engine Report W5

Hello again,

This week I started with fixing a crash in LightweightEQ, which is an Equalizer Effect for low-performance hardware. The problem was the id's of the effect parameters, they were not correctly set. So I have fixed that by assigning the following ids for the knobs: "eq_low", "eq_mid" and "eq_high". On top of that, I removed dry mixing both from LightweightEQ and EQDefault. However, I talked with Daniel and we plan to reintroduce that to the effect which uses Bessel filters.

I am happy to inform you that I'm making progress towards my goal of replacing the Default EQ from enginefilterblock.cpp with an Equalizer Effect. I have finally managed to add switch type parameters to the Effects framework. The last bug was a typo Daniel pointed me out in effectbuttonparameterslot.cpp. I was calling getParameter() method instead of getButtonParameter() inside loadEffect(). Prior to fixing this, the buttons were not updating correctly, they were dependent to their corresponding knob. All they need now is a bit of code refactoring, because some code is duplicated, especially in effectbuttonparameterslot.cpp which contains the class for handling Button parameters.

For the EQ Effect Rack I broken down my work in the following parts:

• Add a new EffectRack (done)
• Modify Deere skin to display that additional Rack (done)
• Add EQ Effects to the newly created Rack
• For this part I chose to instantiate one Effect per each deck. In order to achieve this, I could instantiate 4 Effects as this is the current maximum number of decks. But Mixxx can have an arbitrary number of decks, so it seemed natural for me to create a new EffectUnit and instantiate a new EQ Effect whenever a deck is added. I did this by inserting a method (addEqualizer) at the end of PlayerManager::addDeckInner(). This method is also responsible for setting the effect to be fully wet.
• Allow aliases for controls (in progress)
• We need to make the transition as smooth as possible and this means we still want to handle the newly added EQ Effects with [ChannelX]filter[Low/Mid/High]. The most interesting way of achieving this is to add support for control aliases, a feature which is requested on the bug tracker too[1].

You can see my work on the EQ EffectRack and switch type parameters here[2].

Yours truly,
Nicu Badescu

[1] - https://bugs.launchpad.net/mixxx/+bug/1273953
[2] - https://github.com/badescunicu/mixxx/compare/kill_buttons
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