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47 lines
3.5 KiB
47 lines
3.5 KiB
7 months ago
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# Development
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The effects included are designed to be as portable as possible, as well as making it easy to add additional effects.
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## Building
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To build the app, simply open the project in android studio and build. The app integrates Oboe via a git submodule. Make sure
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when cloning the repository to clone the submodule as well using `git clone --recursive`, or `git submodule update --init --recursive`.
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To update the version of Oboe being used, descend into the Oboe repository [(oboe location)](../app/src/main/cpp)
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and update from its remote. Then, call `git submodule update` in this repository. Alternatively `git submodule update --recursive --remote` will pull the latest version of Oboe from remote.
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Although the CMake file requires android headers (to use Oboe), the effects themselves can be compiled with any C++17 compliant compiler.
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## Architecture
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The UI code (Kotlin) calls native code through the JNI bridge to query information about the various effects implemented,
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and how to render the effect information in the UI. This means that adding an effect only needs to be done on the
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native side. The JNI bridge passes information regarding implemented effects descriptions to the UI as well as functions
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called when the user modifies effects in the UI.
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The `DuplexEngine` is responsible for managing and syncing the input and output Oboe streams for rendering audio
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with as low latency as possible. The `FunctionList` class contains the a vector of effects that correspond to the list of
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effects (and their parameters) that the user wants to use to process their audio. Effects (and the `FunctionList`) overload
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their function operator to take in two numeric iterator types. E.g `<template iter_type> void operator()
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(iter_type begin, iter_type end)`, where the `iter_types` correspond to C++ iterators carrying audio data. To erase the type
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of different objects, the `FunctionList` holds objects of types `std::function<void(iter_type, iter_type)>` i.e. functions
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which operate on the range between two numeric iterators in place. The `DuplexEngine`simply calls the `FunctionList` on every
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buffer of samples it receives.
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The effects folder contains the classes of various implemented effects. It also contains `Effects.h` where a global tuple of
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all the Effect descriptions implemented lives. The description folder contains the description for all of the effects.
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Each description takes the form of a class with static methods providing information regarding the effect (including name,
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category, parameters, and a factory method).
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## Adding Effects
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To add an effect, simply add a Description class similar to the existing classes, and add the class to the tuple in `Effects.h`. The description must provide a way to build the effect by either constructing another class corresponding
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to an effect, or pointing to a standalone function. Adding new effects is welcome!
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## Existing Effects
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A instructional implemented effect to examine is the `TremoloEffect.h` (a modulating gain).
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Many of the effects in the delay category
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inherit from `DelayLineEffect` which provides a framework to easily implement many delay based effects, as well as
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the comb filter effects (FIR, IIR, allpass). The slides have a block diagram displaying the mathematical basis of the effect.
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The nonlinear effects (distortion and overdrive) are implemented using a standalone function (from `SingleEffectFunctions.h`.
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The gain effect is implemented by a simple lambda in its description class.
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