Unreal 4 - Playing Sounds from C++ with Sound Cue using Sound Parameters (Sound Component)

Hopefully you're here if you want it clearly stated how to manipulate a sound-cue from C++ without relying on any blueprint.  I'm going to assume just about zero knowledge, so for the more experienced you may want to skip down to the code sections.

I'm powering my computer with a bicycle..., just show me the code!: (copyable code-blocks below)

Using: USoundCue UAudioComponent from C++, C (no blueprints needed)

The final result of our pitch modulated Sound Cue

Sound cue refresher (skip me if you're familiar with a sound cue)

A sound cue represents an encapsulated group of logic around a sound or sounds. A sound cue can switch between playing multiple sounds, apply effects to the sound based on input, etc.  To the engine, a sound cue is a singular object/sound, but may contain quite a lot of complexity, and mix together many different sounds.  Sound cue's contain parameters just like materials contain parameters, and these parameters can be set during runtime to manipulate how the sound-cue behaves.  In our case we are going to modify a modulation parameter to control the pitch of a looping sound cue. 

Setup our sound cue in the editor (skip me if you have a sound cue w/parameters)

Step 1.) Create a new sound cue (content browser - Add New - sounds - sound cue)

Step 2.) Save the sound-cue with a name (in my case 'airplane-engine') and open it.









Step 3.) Add a Wave Player to the Sound Cue.

Step 4.) Add a Continuous Modulator to the Sound Cue

Step 5.) Connect Wave Player to Modulator to Output.








Step 6.) Click on the Wave Player to configure it, and set what sound it plays (.wav file)

In our case, I want the sound to loop continiously, so I check 'Looping'.

Step 7.) Configure the modulator

It's important the parameter value is set, in my case I only care about manipulating pitch at runtime, and not volume, however you can set parameters for both if you need to manipulate both during runtime.  We will use this parameter name 'pitch' later in our code.

 Step 8.) My real configuration for my propeller

Step 9.) Save the cue and close it...

Code Configuration

First, I'm going to place all my logic in a Pawn class that inherits from AActor... you can theoretically place your sound logic anywhere, but this example will include a pawn.

Step 1.) We need to setup some fields in our header to hold references to our objects.  Ensure you use the UPROPERTY() macros, as this prevents unreal from garbage collecting the object before it should.

Create a pawn class and in your header file ensure these properties and methods are defined.

	UCLASS()
	class FLIGHTMODEL_API AAircraftPawn : public APawn
	{
	GENERATED_BODY()
	public:
	// Sets default values for this pawn's properties
	AAircraftPawn();
	// Called when the game starts or when spawned
	virtual void BeginPlay() override;
	virtual void PostInitializeComponents() override;
	// Called every frame
	virtual void Tick(float DeltaSeconds) override;
	private:
	UPROPERTY(BlueprintReadOnly, Category = "Audio")
	USoundCue* propellerAudioCue;
	UPROPERTY(BlueprintReadOnly, Category = "Audio")
	USoundCue* propellerStartupCue;
	UPROPERTY(BlueprintReadOnly, Category = "Audio")
	UAudioComponent* propellerAudioComponent;
	};

view raw AircraftPawn.h hosted with ❤ by GitHub

Step 2.) We need to configure our constructor to get references to and configure our sound objects.

	// Sets default values
	AAircraftPawn::AAircraftPawn()
	{
	// Set this pawn to call Tick() every frame. You can turn this off to improve performance if you don't need it.
	PrimaryActorTick.bCanEverTick = true;
	// Load our Sound Cue for the propeller sound we created in the editor... note your path may be different depending
	// on where you store the asset on disk.
	static ConstructorHelpers::FObjectFinder<USoundCue> propellerCue(TEXT("'/Game/airplane-engine.airplane-engine'"));
	// Store a reference to the Cue asset - we'll need it later.
	propellerAudioCue = propellerCue.Object;
	// Create an audio component, the audio component wraps the Cue, and allows us to ineract with
	// it, and its parameters from code.
	propellerAudioComponent = CreateDefaultSubobject<UAudioComponent>(TEXT("PropellerAudioComp"));
	// I don't want the sound playing the moment it's created.
	propellerAudioComponent->bAutoActivate = false; // don't play the sound immediately.
	// I want the sound to follow the pawn around, so I attach it to the Pawns root.
	propellerAudioComponent->AttachParent = RootComponent;
	// I want the sound to come from slighty in front of the pawn.
	propellerAudioComponent->SetRelativeLocation(FVector(100.0f, 0.0f, 0.0f));
	}

view raw AircraftPawn-Constructor.cpp hosted with ❤ by GitHub

Step 3.) We need to add our Sound Cue to our Audio Component, which you should avoid doing in the constructor, so we'll perform the same action in PostInitializeComponents()

	void AAircraftPawn::PostInitializeComponents()
	{
	Super::PostInitializeComponents();
	if (propellerAudioCue->IsValidLowLevelFast()) {
	propellerAudioComponent->SetSound(propellerAudioCue);
	}
	}

view raw AircraftPawn-PostInitializeComponents.cpp hosted with ❤ by GitHub

Step 4.) When our pawn is spawned (-1 for rhyming) we need to have it start playing the Cue audio. You may want to do this based on some other event, but for my needs I want the sound to start playing on BeginPlay

	// Called when the game starts or when spawned
	void AAircraftPawn::BeginPlay()
	{
	Super::BeginPlay();
	// Note because the Cue Asset is set to loop the sound,
	// once we start playing the sound, it will play
	// continiously...
	// You can fade the sound in...
	float startTime = 9.f;
	float volume = 1.0f;
	float fadeTime = 1.0f;
	propellerAudioComponent->FadeIn(fadeTime, volume, startTime);
	// Or you can start playing the sound immediately.
	propellerAudioComponent->Play();
	}

view raw AircraftPawn-BeginPlay.cpp hosted with ❤ by GitHub

Step 5.) Each frame we need to update the sound parameter pitch based on our engines speed.

	// Called every frame
	void AAircraftPawn::Tick(float DeltaTime)
	{
	// Modulate the pitch of the sound cue by passing in the RPM of the aircraft propeller
	// Notice we reference the parameter we set in the Cue Object here: 'pitch'.
	float propRpm = propeller->lastEngineRpm * propeller->reductionRatio;
	propellerAudioComponent->SetFloatParameter(FName("pitch"), propRpm);
	}

view raw AircraftPawn-Tick.cpp hosted with ❤ by GitHub