Awesome
Spectrum
<img src="https://github.com/boourns/Spectrum/raw/master/marketing/screenshots/spectrum-main.jpg" width=400/>AudioUnit ports of popular open source eurorack modules
Available on App Store for iOS: https://apps.apple.com/us/app/spectrum-synthesizer-bundle/id1467384251
Building
Spectrum depends on two other git repositories to build: BurnsAudioCore and BurnsAudioUnit. The Spectrum xcode workspace expects these three git repositories to all be siblings in a directory. So for example,
mkdir auv3
cd auv3
git clone git@github.com:boourns/Spectrum.git
git clone git@github.com:boourns/BurnsAudioCore.git
git clone git@github.com:boourns/BurnsAudioUnit.git
open Spectrum/Spectrum.xcworkspace
Exploring the code
Each AudioUnit is broken down into the following components. You can find the code under the Instrument subdirectory. Audio Units with both an Effect and an Instrument version have a Shared folder holding the shared code. For example, here is the code for the Spectrum instrument.
AudioUnit.mm / AudioUnit.h (Objective-C)
Root AudioUnit class. Responsible for parameter registration, initializing and managing buffers, instantiating the C++ "kernel" where the DSP code is written. The internalRenderBlock callback is in this class, which the host calls for every render block.
ViewController (swift)
Provides the UI for the Audio Unit. The parent class, BaseAudioUnitViewController, is provided in BurnsAudioCore and handles connecting the UI to the Audio Unit instance.
Kernel (C++)
The exciting DSP code. Reads/writes parameter values into the C++ engine, contains the DSP render block. In our case it mostly manages the Mutable Instruments code and calls those DSP engines.
There are many independent, reusable components available in the other repositories, for example helper classes for initializing AudioUnit buffers, a tempo-synced LFO, or a MPE-capable MIDI processor / voice manager in BurnsAudioUnit.
License
MIT