This is full-featured AUv3 effect that acts like the phaser stomp boxes of old. It is for both iOS and macOS platforms. When configured, it will build an app for each platform and embed in the app an app extension containing the AUv3 component. The apps are designed to load the component and use it to demonstrate how it works by playing a sample audio file and routing it through the effect.
Additional features and info:
- uses an Objective-C++ kernel for audio sample manipulation in the render thread
- provides a very tiny Objective-C interface to the kernel for access with Swift
- uses Swift for all UI and all audio unit work not associated with rendering
The code was developed in Xcode 12.4 on macOS 11.2.1. I have tested on both macOS and iOS devices primarily in GarageBand, but also using test hosts on both devices as well as the excellent AUM app on iOS.
Finally, it passes all auval tests:
% auval -v aufx phzr BRay
This effect is based on a design described in the excellent book "Designing Audio Effects Plugins in C++" by Will Pirkle. His design uses six all-pass filters to do the phase shifting in 6 overlapping bands ranging from 16Hz to 20kHz. In the book, he mentions that his design was "derived from the analog ciruit in the National Semiconductor (NSC) Audio/Radio Handbook, a 1970s source of old App Notes from National Semiconductor... The NSC design used six 1st order all-pass stages that were modulated from a common LFO."
You can find Pirkle's implementation in the fxobjects.h file. Note that the effect uses my own C++ implementation that I think is a bit more straightforward. There are unit tests that compare the two for implementation correctness.
Note that most of the the C++ code that does the filtering is found in the AUv3Support Swift package that this project depends on. The PhaseShifter.hpp class contains the pipeline that does the filtering on the samples. It relies on a collection of 6 biquad filters configured in all-pass mode.
The macOS and iOS apps are simple hosts that demonstrate the functionality of the AUv3 component. In the AUv3 world, an app serves as a delivery mechanism for an app extension like AUv3. When the app is installed, the operating system will also install and register any app extensions found in the app.
The SimplyPhaser apps attempt to instantiate the AUv3 component and wire it up to an audio file player and the
output speaker. When it runs, you can play the sample file and manipulate the filter settings -- cutoff
frequency in the horizontal direction and resonance in the vertical. You can control these settings either by
touching on the graph and moving the point or by using the sliders to change their associated values. The
sliders are somewhat superfluous but they act on the AUv3 component via the AUPropertyTree much like an external
MIDI controller might do.
Each OS (macOS and iOS) app has the same basic layout:
App-- code and configury for the application that hosts the AUv3 app extensionExtension-- code and configury for the extension itself
However, most of the code you will find elsewhere, either in the Swift Packages Sources folder that holds some code and resources common to both platforms, or more likely in the AUv3Support Swift package mentioned above.
⚠️ You are free to use the code according to LICENSE.md, but you must not replicate someone's UI, icons, samples, or any other assets if you are going to distribute your effect on the App Store.
Feel free to fork and do as you please. If you have improvements, I would definitely welcome your feedback. If you are interested in working out your own AUv3 plugins have a look at my AUv3Template project which tries to offer a good place to start with something that you can call your own.