Sample CodeiOS, iPadOS, Mac Catalyst, macOSReviewed 2026-07-21View on Apple Developer

Building a signal generator

At a glance

Item	Summary
Purpose	Generates selectable waveforms in a custom real-time audio source node.
App architecture	SwiftUI state flows through a Swift manager and Objective-C++ adapter to a C++ DSP kernel.
Main patterns	Observable manager, language-bridge adapter, render callback, waveform strategy table, parameter ramping.
Project style	Single app target organized by language boundary rather than feature folders.

Project structure

SignalGenerator/
├── SignalGeneratorApp.swift
├── ContentView.swift
├── AudioManager.swift
├── SignalGenerator.h
├── SignalGenerator.mm
├── SignalGeneratorKernel.h
├── ParameterRamp.h
└── WaveFunction.h

Structure observations

Swift owns presentation and engine composition; Objective-C++ is the narrow interoperability seam.
Header-only C++ types isolate sample generation, ramping, and waveform selection from UI concerns.

Overall architecture

flowchart LR
    UI["SwiftUI controls"] --> Manager["AudioManager"]
    Manager --> Bridge["SignalGenerator ObjC++"]
    Bridge --> Kernel["SignalGeneratorKernel C++"]
    Kernel --> Ramp["ParameterRamp"]
    Kernel --> Wave["WaveFunction table"]
    Bridge --> Source["AVAudioSourceNode render block"]
    Source --> Engine["AVAudioEngine → output"]

Reference code

SignalGenerator/AudioManager.swift:32 — the manager connects the render callback to the engine graph.

let srcNode = AVAudioSourceNode(renderBlock: signalGenerator.renderBlock)
let mainMixer = engine.mainMixerNode
let output = engine.outputNode
signalGenerator.setSampleRate(outputFormat.sampleRate)
engine.attach(srcNode)
engine.connect(srcNode, to: mainMixer, format: inputFormat)
engine.connect(mainMixer, to: output, format: outputFormat)

Interpretation

AudioManager is the application façade. Parameter changes cross the Objective-C interface, while audio-frame production remains in C++ and is invoked by AVAudioEngine’s real-time callback.

Ownership and state

classDiagram
    SignalGeneratorApp *-- AudioManager : State owns
    AudioManager *-- AVAudioEngine : owns
    AudioManager *-- SignalGenerator : owns
    SignalGenerator *-- SignalGeneratorKernel : C++ ivar
    SignalGenerator *-- SignalGeneratorParameters : C++ ivar
    AVAudioEngine --> SignalGenerator : invokes render block

Ownership evidence

SignalGenerator/AudioManager.swift:10 — the manager retains the bridge and engine as private implementation objects.

@Observable class AudioManager {
    // ...
}

Owner	Object or state	Relationship	Mutation authority
`SignalGeneratorApp`	`AudioManager`	Creates with `@State` and binds into the view	`AudioManager` and bound UI properties
`AudioManager`	Engine, bridge, UI-facing parameters	Creates and retains	`AudioManager`
`SignalGenerator`	Kernel and pending parameter struct	Embedded Objective-C++ ivars	Bridge setters/render block
`SignalGeneratorKernel`	Phase, ramps, waveform function	Value-owned DSP state	Kernel methods on render path

Class and protocol design

Type	Responsibility	Depends on
`AudioManager`	Map observable controls to DSP setters and compose the audio graph	AVAudioEngine, `SignalGenerator`
`SignalGenerator`	Present a Swift/Objective-C-compatible API and render block	C++ kernel
`SignalGeneratorKernel`	Produce the next sample from smoothed parameters	`ParameterRamp`, `WaveFunction`
`ParameterRamp`	Move parameter values without abrupt discontinuities	C++ numeric state
`WaveFunction`	Select waveform calculation by enum	Function-pointer table

Access control

Symbol	Access	Verified effect	Likely rationale
`AudioManager.signalGenerator` / `engine`	`private`	UI code cannot rewire the graph or access DSP internals.	Keep graph invariants centralized.
`SignalGenerator` header methods	Objective-C interface	Swift sees only render/setup/parameter operations.	Make the bridge deliberately narrow.
Kernel implementation state	C++ `private`	Callers use setup/update/sample methods rather than phase fields.	Protect DSP invariants.
`Waveform` description witnesses	`public`	Satisfy public protocol requirements used by the UI.	Language conformance requirement, not a public framework architecture.
Swift app types	implicit `internal`	Remain within the app module.	The target is an app, not a library.

Reference code

SignalGenerator/SignalGenerator.mm:19 — C++ ownership is hidden inside the adapter implementation.

@implementation SignalGenerator {
    // ...
}
// ...
@end

Logic ownership and placement

Logic	Owning type or file	Placement rationale
Control state and engine lifecycle	`AudioManager`	Swift-observable application layer.
Inter-language conversion and callback	`SignalGenerator.mm`	Only file that needs Objective-C and C++ together.
Per-frame DSP	`SignalGeneratorKernel.h`	Real-time logic stays independent of UI/runtime bridging.
Smoothing	`ParameterRamp.h`	Reusable numerical responsibility.
Waveform algorithms	`WaveFunction.h`	Compact strategy selection.

Design patterns

Pattern	Source evidence	Purpose or tradeoff
Observable façade	`SignalGenerator/AudioManager.swift:10`	Gives UI one coherent audio API.
Adapter/bridge	`SignalGenerator/SignalGenerator.mm:45`	Exposes a C++ kernel as an AVAudio source-node block.
Strategy table	`SignalGenerator/WaveFunction.h:13`	Selects waveform behavior without a class hierarchy.
Parameter ramp	`SignalGenerator/ParameterRamp.h:12`	Reduces artifacts from control changes.
Real-time callback	`SignalGenerator/SignalGenerator.mm:51`	Lets AVAudioEngine request exactly the frames it needs.

Naming conventions

Manager and kernel suffixes communicate layer and role: AudioManager, SignalGeneratorKernel.
Setters mirror domain controls: setFrequency, setAmplitude, setWaveform, setSampleRate.
File extensions expose the language boundary: .swift, .mm, and header-only C++ .h.
Waveform names domain choices; WaveFunction names executable strategies.

Architecture takeaways

Put Objective-C++ in a narrow adapter so most app code remains idiomatic Swift or C++.
Keep engine graph ownership in one manager and per-frame work in a small kernel.
Copy UI parameters into render-owned state once per callback, not through repeated object lookup per sample.
Use access control to prevent presentation code from mutating the audio graph directly.

Source map

Source file	Relevant symbols
`SignalGenerator/SignalGeneratorApp.swift`	App-owned `AudioManager`
`SignalGenerator/AudioManager.swift`	Observable state and engine graph
`SignalGenerator/SignalGenerator.h`	Bridge contract
`SignalGenerator/SignalGenerator.mm`	Bridge implementation and render block
`SignalGenerator/SignalGeneratorKernel.h`	DSP kernel
`SignalGenerator/ParameterRamp.h`	Parameter smoothing
`SignalGenerator/WaveFunction.h`	Waveform functions

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