Equalizing audio with discrete cosine transforms (DCTs)

At a glance

Project structure

Source bundle/
├── AudioEqualization/
│   ├── AudioEqualizationApp.swift
│   ├── DrumLoopProvider.swift
│   ├── ContentView.swift
│   ├── AudioUtilities.swift
│   └── AudioEqualization.entitlements
├── Audio-Equalization.xcodeproj/
│   ├── .xcodesamplecode.plist
│   └── project.pbxproj
└── Configuration/
    └── SampleCode.xcconfig

Structure observations

• Architecturally prominent files are ranked from entry points and role-named declarations; resource-only paths are omitted.
• Primary languages: Swift.
• The verified tree contains 4 project/configuration file(s) and 7 source declaration(s).

Overall architecture

flowchart LR
    N1["AudioEqualizationApp"]
    N2["ContentView"]
    N3["DrumLoopProvider"]
    N4["Accelerate APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4

Reference code

AudioEqualization/AudioEqualizationApp.swift:10 — architecture anchor

@main
struct AudioEqualizationApp: App {

    @Environment(\.scenePhase) private var scenePhase

    // The `drumLoopProvider` object provides the drum loop and exposes an API
    // to apply audio equalization.
    let drumLoopProvider = DrumLoopProvider()

    var body: some Scene {
        WindowGroup {
            ContentView()
                .environmentObject(drumLoopProvider)
        }
        .onChange(of: scenePhase) { phase in
            if phase == .active {
                Task(priority: .userInitiated) {
                    try? await drumLoopProvider.loadAudioSamples()
                    try? SignalGenerator(signalProvider: drumLoopProvider).start()
                }
            }
        }
    }
}

Interpretation

The arrows summarize the source-visible entry, role-named types or folders, and framework direction; when nodes come from structural folders, the sequence is a high-level interpretation rather than proof that every adjacent node calls the next. Ownership is claimed only where the next section cites a stored property or assignment. The diagram is intentionally limited to the dominant path into Accelerate.

Ownership and state

classDiagram
    AudioEqualizationApp *-- DrumLoopProvider : drumLoopProvider
    DrumLoopProvider *-- Array : envelope
    DrumLoopProvider *-- Array : equalizedFrequencyDomainSignal
    DrumLoopProvider *-- Array : equalizedTimeDomainSignal

Ownership evidence

AudioEqualization/AudioEqualizationApp.swift:17 — stored dependency or nearest verified ownership anchor

@main
struct AudioEqualizationApp: App {
    // ...
    let drumLoopProvider = DrumLoopProvider()
    // ...
}

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

AudioEqualization/AudioEqualizationApp.swift:26 — representative execution boundary

                Task(priority: .userInitiated) {
                    try? await drumLoopProvider.loadAudioSamples()
                    try? SignalGenerator(signalProvider: drumLoopProvider).start()
                }

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

AudioEqualization/AudioUtilities.swift:160 — representative type boundary

protocol SignalProvider {
    func getSignal() -> [Float]
    var sampleRate: CMTimeScale { get }
}

The source explicitly defines local protocol relationships: DrumLoopProvider → SignalProvider.

Access control

Reference code

AudioEqualization/AudioEqualizationApp.swift:13 — representative boundary

@main
struct AudioEqualizationApp: App {
    // ...
    @Environment(\.scenePhase) private var scenePhase
    // ...
}

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: App: AudioEqualizationApp; Generator: SignalGenerator; Provider: DrumLoopProvider, SignalProvider; View: ContentView.
• Protocols: SignalProvider.
• Methods: updateEnvelope, loadAudioSamples, apply, getSignal, updatePath, getAudioSamples, start, getSignalElement.
• Files: AudioEqualization/AudioEqualizationApp.swift, AudioEqualization/DrumLoopProvider.swift, AudioEqualization/ContentView.swift, AudioEqualization/AudioUtilities.swift.

Architecture takeaways

• AudioEqualizationApp is the main source-visible entry or composition anchor for this sample.
• Framework work reaches Accelerate, SwiftUI, AVFoundation 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