Applying biquadratic filters to a music loop

At a glance

Project structure

Source bundle/
├── vDSP-Biquad-Coefficients-Calculator/
│   ├── BiquadCoefficientsCalculatorApp.swift
│   ├── FilterableMusicProvider.swift
│   ├── ContentView.swift
│   ├── AudioUtilities.swift
│   ├── BiquadCoefficientCalculator.swift
│   └── MagnitudeResponseCalculator.swift
├── Configuration/
│   └── SampleCode.xcconfig
└── vDSP-Biquad-Coefficients-Calculator.xcodeproj/
    ├── .xcodesamplecode.plist
    └── project.pbxproj

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 3 project/configuration file(s) and 11 source declaration(s).

Overall architecture

flowchart LR
    N1["BiquadCoefficientsCalculatorApp"]
    N2["ContentView"]
    N3["FilterableMusicProvider"]
    N4["Accelerate APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4

Reference code

vDSP-Biquad-Coefficients-Calculator/BiquadCoefficientsCalculatorApp.swift:11 — architecture anchor

@main
struct BiquadCoefficientsCalculatorApp: App {

    @Environment(\.scenePhase) private var scenePhase

    // The `musicProvider` object provides the music loop and exposes an API
    // to filter the music loop using a biquadratic filter.
    let musicProvider = FilterableMusicProvider()

    var body: some Scene {
        WindowGroup {
            ContentView()
                .environmentObject(musicProvider)
                .onChange(of: scenePhase) { phase in
                    if phase == .active {
                        Task(priority: .userInitiated) {
                            try? await musicProvider.loadAudioSamples()
                            try? SignalGenerator(signalProvider: musicProvider).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
    BiquadCoefficientsCalculatorApp *-- FilterableMusicProvider : musicProvider
    Parameters o-- Filtertype : filterType
    Parameters o-- Frequency : frequency
    Parameters o-- Q : Q

Ownership evidence

vDSP-Biquad-Coefficients-Calculator/BiquadCoefficientsCalculatorApp.swift:18 — stored dependency or nearest verified ownership anchor

@main
struct BiquadCoefficientsCalculatorApp: App {
    // ...
    let musicProvider = FilterableMusicProvider()
    // ...
}

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

vDSP-Biquad-Coefficients-Calculator/AudioUtilities.swift:18 — representative execution boundary

    static func getAudioSamples(forResource: String,
                                withExtension: String) async throws -> (naturalTimeScale: CMTimeScale,
                                                                        data: [Float])? {
        // ...
            return nil
        // ...
    }

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

vDSP-Biquad-Coefficients-Calculator/AudioUtilities.swift:160 — representative type boundary

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

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

Access control

Reference code

vDSP-Biquad-Coefficients-Calculator/AudioUtilities.swift:84 — representative boundary

class SignalGenerator {
    private let engine = AVAudioEngine()
    // ...
}

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: BiquadCoefficientsCalculatorApp; Generator: SignalGenerator; Provider: FilterableMusicProvider, SignalProvider; View: ContentView.
• Protocols: SignalProvider.
• Methods: loadAudioSamples, setSelectedSectionCoefficients, getSignal, makeFrequencyDomainWaveform, updatePath, getAudioSamples, start, getSignalElement.
• Files: vDSP-Biquad-Coefficients-Calculator/BiquadCoefficientsCalculatorApp.swift, vDSP-Biquad-Coefficients-Calculator/FilterableMusicProvider.swift, vDSP-Biquad-Coefficients-Calculator/ContentView.swift, vDSP-Biquad-Coefficients-Calculator/AudioUtilities.swift, vDSP-Biquad-Coefficients-Calculator/BiquadCoefficientCalculator.swift, vDSP-Biquad-Coefficients-Calculator/MagnitudeResponseCalculator.swift.

Architecture takeaways

• BiquadCoefficientsCalculatorApp 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