Extending The Effects Engine Report W1

#1 Weekly Report

Hello,

A week has passed since Google Summer of Code '14 has started and I'm enjoying every moment of it. With constant help from my mentor, Daniel Schürmann, I have managed to do most of the work towards moving the current EQ into the effect space. The newly created EQ effect behaves exactly like the current equalizer. It uses three EngineFilterButterworths instantiated with a sample rate which is fetched from the engine and two corner frequencies which are obtained from the preferences "Equalizers" menu.

Here are the steps I took in order to achieve an EQ Effect, which is intended to be a copy of the default equalizer:

• Create a new EqEffectGroupState class which stores three EngineFilterButterworth for processing the signal
• Create a new EqEffect class which handles the processGroup method and contains three EngineEffectParameters and two ControlObjectSlaves
• Create an EffectManifest for the current effect and add three parameters to it; these parameters are the knobs which are responsible for controlling the equalizer's low, mid and high filters

       * The parameter insertion is done via EffectManifest::addParameter() which returns a reference to the newly added parameter which can be modified however we desire through its "set*" methods
* Connect the two ControlObjectSlaves to "LoEQFrequency" and "HiEQFrequency" to be able to fetch the user's frequency preferences
* Add a new ControlObjectSlave field to GroupEffectProcessor class (m_pSampleRate); this field provides the current sample rate to the effects framework
       * Initially, I and Daniel thought of creating it as a static field inside GroupEffectProcessor, but being a static field it meant its lifetime will end at the end of the program, which isn't something desirable
* Register the newly created effect with NativeBackend, using NativeBackend::registerEffect<T> method
       * registerEffect<T> method goes all the way down to EffectProcessorInstantiator::instantiate method which calls T's constructor

Work still to be done:

• fix this bug https://bugs.launchpad.net/mixxx/+bug/1209294
• find a way of implementing switch type parameters (needed for "kill" buttons)

       * an idea would be introducing a new type of Parameter set
       * another idea would be changing the EffectParameterSlot::m_pControlValue to a more generic class which will handle both the Potmeters and the PushButtons

The branch I'm working on can be seen here: eq_effect_branch

Stay tuned for updates!
Nicu Badescu

Back to the main page!