Creating custom audio effects

At a glance

Project structure

Source bundle/
├── Shared/
│   ├── Support/
│   │   ├── User Interface/
│   │   │   └── FilterView.swift
│   │   └── Audio/
│   │       └── SimplePlayEngine.swift
│   ├── AudioUnitManager.swift
│   ├── AUv3FilterDemoViewController.swift
│   └── AudioUnit/
│       ├── Support/
│       │   ├── FilterDSPKernelAdapter.h
│       │   ├── FilterDSPKernelAdapter.mm
│       │   └── AUv3Base.mm
│       └── AUv3FilterDemoParameters.swift
├── iOS/
│   └── AUv3Filter/
│       ├── AppDelegate.swift
│       └── MainViewController.swift
└── macOS/
    └── AUv3Filter/
        ├── AppDelegate.swift
        └── MainViewController.swift

Structure observations

• Architecturally prominent files are ranked from entry points and role-named declarations; resource-only paths are omitted.
• Primary languages: C/Objective-C header, Objective-C++, Swift.
• The verified tree contains 17 project/configuration file(s) and 18 source declaration(s).

Overall architecture

flowchart LR
    Bundle["Sample bundle"]
    V1["iOS"]
    V2["macOS"]
    Boundary["AUv3FilterFramework / CoreAudioKit APIs"]
    Bundle --> V1
    V1 --> Boundary
    Bundle --> V2
    V2 --> Boundary

Reference code

iOS/AUv3Filter/AppDelegate.swift:10 — architecture anchor

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?

}

Interpretation

The branches represent separate entry-bearing project variants in the downloaded bundle, not runtime calls between those variants. Each branch is intentionally collapsed at the documented framework boundary; the detailed target-local flow remains in the cited files. Ownership is claimed only where the next section cites a stored property or assignment.

Ownership and state

classDiagram
    FilterView *-- Float : defaultMinHertz
    FilterView *-- Float : defaultMaxHertz
    FilterView *-- CGFloat : leftMargin
    FilterView *-- CGFloat : rightMargin

Ownership evidence

Shared/Support/User Interface/FilterView.swift:8 — stored dependency or nearest verified ownership anchor

public let defaultMinHertz: Float = 12.0

Composition arrows indicate a source-visible construction expression or locally owned value state; aggregation means the owner stores or receives a dependency without proving exclusive lifetime ownership.

Concurrency, scheduling, and thread safety

Evidence limit: actor isolation, async/await, or Task creation does not by itself prove background-thread execution; Sendable conformance alone does not prove thread-safe mutation.

@MainActor/MainActor.run, DispatchQueue.main, and RunLoop.main are reported as distinct isolation, queue, and event-loop mechanisms. A plain Task is kept separate from Task.detached; neither is labeled as a background thread.

Reference code

Shared/AUv3FilterDemoViewController.swift:124 — representative execution boundary

            DispatchQueue.main.async {
                self.updateUI()
            }

State propagation, frameworks, and dependencies

Evidence limit: an import proves a source-level compilation dependency at the cited line; it does not prove runtime use, architectural adoption, or whether a Swift package is a direct application dependency.

receive(on:) describes downstream delivery scheduling, while subscribe(on:) describes upstream subscription/request/cancel scheduling. An import Combine alone establishes neither behavior nor a Store, reducer, Redux, or other application architecture.

Class and protocol design

Shared/Support/User Interface/FilterView.swift:12 — representative type boundary

protocol FilterViewDelegate: AnyObject {
    func filterViewTouchBegan(_ filterView: FilterView)
    // ...
}

The source explicitly defines local protocol relationships: AUv3FilterDemoViewController → FilterViewDelegate, MainViewController → AUManagerDelegate, MainViewController → AUManagerDelegate.

Access control

Reference code

Shared/AUv3FilterDemoViewController.swift:15 — representative boundary

public class AUv3FilterDemoViewController: AUViewController {
    // ...
    private var viewConfig: AUAudioUnitViewConfiguration!
    // ...
}

Swift declarations without a modifier are internal; explicit private, fileprivate, private(set), public, or open entries above are interpreted by language semantics. Objective-C/C samples instead rely on header and implementation boundaries, which are not equivalent to Swift lexical privacy.

Logic ownership and placement

Design patterns

Naming conventions

• Types: Adapter: FilterDSPKernelAdapter; Controller: AUv3FilterDemoViewController, MainViewController; Delegate: AUManagerDelegate, AppDelegate, FilterViewDelegate; Engine: SimplePlayEngine; Manager: AudioUnitManager; Player: InstrumentPlayer; View: FilterView.
• Protocols: FilterViewDelegate, AUManagerDelegate.
• Methods: filterViewTouchBegan, filterView, filterViewTouchEnded, filterViewDataDidChange, clamp, noAnimation, valueAtGridIndex, logValueForNumber.
• Files: Shared/Support/User Interface/FilterView.swift, iOS/AUv3Filter/AppDelegate.swift, macOS/AUv3Filter/AppDelegate.swift, Shared/AudioUnitManager.swift, Shared/Support/Audio/SimplePlayEngine.swift, Shared/AUv3FilterDemoViewController.swift.

Architecture takeaways

• AppDelegate is the main source-visible entry or composition anchor for this sample.
• Framework work reaches AUv3FilterFramework, CoreAudioKit, AVFoundation, AudioToolbox through a deliberately small high-level chain; the detailed API graph remains inside the cited implementation files.
• Stored-property evidence identifies lifecycle collaboration; it does not by itself prove exclusive object ownership.
• Access-control conclusions separate verified language visibility from the likely design rationale.
• Local protocol relationships provide an explicit substitution boundary.

Source map

• Official Apple documentation