This is an AUv3 audio effect that creates the iconic "flanging" effect on an audio input. Flanging is a mixture of the same audio signals with one just slightly ahead or behind the other in time. The original effect was created by playing the same audio source from two tape plays and then slowing one or the other down by lightly touching the tape reel flange to very slightly slow down playback. Instead of manually operating two tape decks, here we just use a digital delay to essentially achieve the same result.
It runs on both macOS and iOS. Each OS has its own app which is used to install app extension that is the AUv3 audio effect.
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.
- Depth -- controls how much variation there is in the delay from the original signal.
- Rate -- controls the low-frequency oscillator (LFO) that changes the "depth" value. The higher the number, the faster the oscillation.
- Delay -- the amount of delay from the original signal to induce. The actual delay is based on this but then varies depending on the LFO and the depth setting.
- Feedback -- to really mix things up, you can inject the modified signal back into the delay system. This controls how much of the manipulated signal to inject.
- Dry -- the amount of original signal that is used in the output signal.
- Wet -- the amount of the modified signal that is used in the output signal.
There are two esoteric toggles which can dramatically affect the resulting sound:
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Odd 90° -- the low-frequency oscillator (LFO) of every other input audio channel is 90° out-ot-phase with the rest. For stereo (left and right) inputs and indices starting at zero, the left channel is considered "even" and the right is "odd". Having out-of-phase LFO signals usually results in a fuller sound.
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Negative Feedback -- this affects how a feedback is summed with the input signal before it reaches the delay unit. When negative, the feedback signal is essentially subtracted from the input signal which will dramatically affect the frequencies of the signal sent to the delay unit. Again, this can result in a more interesting and sonically complex effect than the usual summing that is often done.
The row of buttons at the top of the host demonstration app let you play a prerecorded sample throught the effect and try out different pre-installed or "factory" presets. Note that these controls are not present in the audio unit itself, but the factory presets are available from within other AUv3 hosts such as GarageBand -- as are user presets if the host supports them.
This audio unit passes all auval tests, so it should work in your AUv3-compatible host application:
% auval -v aufx flng BRay
To successfully compile you will need to edit Common.xcconfig and change
DEVELOPMENT_TEAM to hold your own Apple developer account ID so you can sign the binaries. You should
also adjust other settings as well to properly identify you and/or your company if you desire.
⚠️ 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.
There are additional values in this file that you really should change, especially to remove any risk of collision with other AUv3 effects you may have on your system.
The script newRelease.sh automates generating new archive versions of both the macOS and iOS
apps and uploads them to the App Store if everything checks out. It uses the DEVELOPMENT_TEAM setting in the
Common.xcconfig to handle the authentication and signing.
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 SimplyFlange 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) have pretty much the same code layout:
App-- code for the application that hosts the AUv3 app extension. Note that most of the code is actually found in the external AUv3Support package.Extension-- UI for the extension. Most of the code is found in the Packages/Sources folder which holds the code for internally-defined Swift packages.
As mentioned above, the Packages folder holds all of the common code that is used by the above products. In it you will find
- FilterAudioUnit -- the actual AUv3 AudioUnit written in Swift.
- Kernel -- the Obj-C++ kernel adapter and C++ classes that perform the rendering of audio samples.
- Parameters -- definitions for the AudioUnit runtime parameters as well as a preset definition using the parameters.
Additional supporting files can be found in the AUv3Support project.