JUCE学习笔记05-音频输出基础（白噪）

JUCE学习笔记05——音频输出基础（白噪）

知识点：

1、AudioAppComponent类基础
2、音频应用程序的生命周期

目标：

了解AudioAppComponent类的三个方法与生命周期、生成白噪音、使用Slider控制音量

内容：

一、理解音频应用程序的生命周期

1、启动应用程序时AudioAppComponent的构造函数中设置输入输出通道数，触发音频处理的启动，并会调用prepareToPlay（）方法，这里通过获取系统默认采样率和缓存区块大小信息实现该方法，并用组件的paint()方法显示在窗口上。

 MainComponent::MainComponent()
{setSize (800, 600);if (RuntimePermissions::isRequired (RuntimePermissions::recordAudio)&& ! RuntimePermissions::isGranted (RuntimePermissions::recordAudio)){RuntimePermissions::request (RuntimePermissions::recordAudio,[&] (bool granted) { if (granted)  setAudioChannels (2, 2); });}else{setAudioChannels (0, 2);//注册输入输出通道}
}

private:String msg;  //调用信息String blockSize;  //缓存区块大小String sysSampleRate;  //默认系统采样率

void MainComponent::prepareToPlay (int samplesPerBlockExpected, double sampleRate)
{msg = "Call: prepareToPlay()";blockSize << samplesPerBlockExpected;sysSampleRate << sampleRate;
}

void MainComponent::paint (Graphics& g)
{g.setFont(30);  //字体大小g.setColour(Colours::red);  //字体颜色g.drawText(msg, 10,10,300,30,Justification::left,false);  //绘制文本g.drawText("Buffer: "+ blockSize, 10, 40, 300, 30, Justification::left, false);g.drawText("SampleRate: "+ sysSampleRate, 10, 70, 300, 30, Justification::left, false);
}

运行效果：

2、关闭应用程序时构造函数中的shutdownAudio()会调用releaseResources()方法释放音频源的缓存、关闭音频处理。

MainComponent::~MainComponent()
{//释放缓存、关闭音频设备shutdownAudio();
}

3、音频应用程序运行中依据音频系统的请求回调getNextAudioBlock ()方法获取播放所需的音频数据

void MainComponent::getNextAudioBlock (const AudioSourceChannelInfo& bufferToFill)
{
//生成播放音频数据的代码
}

二、实现getNextAudioBlock方法生成白噪音

1、白噪音（百度）：白噪声是指在较宽的频率范围内，各等带宽的频带所含的噪声能量
相等的噪声。是一种功率谱密度为常数的随机信号。
简单理解：白噪音是通过在音频流中填充随机数所产生的音频信号

2、生成白噪音的方法

void MainComponent::getNextAudioBlock (const AudioSourceChannelInfo& bufferToFill)
{bufferToFill.clearActiveBufferRegion();  //JUCE自动生成的清理缓存方法，用于避免启动音频处理时爆音Random random; //随机数对象for (int channel = 0; channel < bufferToFill.buffer->getNumChannels(); ++channel)//遍历需填充音频采样数据的通道{float* buffer = bufferToFill.buffer->getWritePointer(channel, bufferToFill.startSample);//缓存块的起始点for (int sampleIndex = 0; sampleIndex < bufferToFill.numSamples; ++sampleIndex) //遍历采样点{buffer[sampleIndex] = (random.nextFloat()*2.0 - 1.0)*0.1;  //写入随机采样值}}
}

三、使用Slider控制音量

1、主组件继承Slider::Listener

 class MainComponent   : public AudioAppComponent,public Slider::Listener

2、创建Slider、设置基本属性、添加至主组件、设置位置

MainComponent::MainComponent()
{addAndMakeVisible(volumeSlider); volumeSlider.setRange(0, 1, 0.01);//......其他代码
}

void MainComponent::resized()
{volumeSlider.setBounds(100, 100, 200, 200);
}

3、创建标签添加至Slider

MainComponent::MainComponent()
{volumeLabel.setText("Volume", NotificationType::dontSendNotification);volumeLabel.attachToComponent(&volumeSlider,true);//......其他代码
}

运行效果：

4、创建音量变量作为随机数的乘数

float volume;

5、实现Listener的sliderValueChanged(Slider * slider)方法，Slider的值与音量绑定

void MainComponent::sliderValueChanged(Slider * slider)
{if (slider == &volumeSlider)volume=volumeSlider.getValue();
}

6、添加Listener至Slider，初始化音量

MainComponent::MainComponent()
{volumeSlider.addListener(this); //Slider上添加监听volume = 0;  //音量默认值
}

7、将音量乘数应用到音频数据流中

void MainComponent::getNextAudioBlock (const AudioSourceChannelInfo& bufferToFill)
{bufferToFill.clearActiveBufferRegion();  //JUCE自动生成的清理缓存方法，用于避免启动音频处理时爆音Random random;for (int channel = 0; channel < bufferToFill.buffer->getNumChannels(); ++channel)//遍历需填充音频采样数据的通道{auto* buffer = bufferToFill.buffer->getWritePointer(channel, bufferToFill.startSample);//缓存块的起始点for (int sampleIndex = 0; sampleIndex < bufferToFill.numSamples; ++sampleIndex) //遍历采样点{buffer[sampleIndex] = (random.nextFloat()*2.0 - 1.0)*volume;// 写入随机采样值}}
}

完整代码：

//MainComponent.h
#pragma once#include "../JuceLibraryCode/JuceHeader.h"//==============================================================================
/*This component lives inside our window, and this is where you should put allyour controls and content.
*/
class MainComponent   : public AudioAppComponent,public Slider::Listener
{
public://==============================================================================MainComponent();~MainComponent();//=============AudioSource类方法================================================void prepareToPlay (int samplesPerBlockExpected, double sampleRate) override;void getNextAudioBlock (const AudioSourceChannelInfo& bufferToFill) override;void releaseResources() override;//=============Component类方法==================================================void paint (Graphics& g) override;void resized() override;//=============Slider::Listener类方法===========================================void sliderValueChanged(Slider* slider) override;private:String msg;  //调用信息String blockSize;  //缓存区块大小String sysSampleRate;  //默认系统采样率Slider volumeSlider; //音量Slider对象Label volumeLabel;float volume;JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (MainComponent)
};

//MainComponent.cpp
#include "MainComponent.h"//==============================================================================
MainComponent::MainComponent()
{setSize (800, 600);addAndMakeVisible(volumeSlider);volumeSlider.setRange(0, 1, 0.01f);volumeLabel.setText("Volume", NotificationType::dontSendNotification);volumeLabel.attachToComponent(&volumeSlider,true);volumeSlider.addListener(this);volume = 0;// Some platforms require permissions to open input channels so request that hereif (RuntimePermissions::isRequired (RuntimePermissions::recordAudio)&& ! RuntimePermissions::isGranted (RuntimePermissions::recordAudio)){RuntimePermissions::request (RuntimePermissions::recordAudio,[&] (bool granted) { if (granted)  setAudioChannels (2, 2); });}else{// 注册所需的输入和输出数，然后触发音频处理并调用prepareToPlay（）方法setAudioChannels (0, 2);}
}MainComponent::~MainComponent()
{//释放缓存、关闭音频设备shutdownAudio();
}//==============================================================================
void MainComponent::prepareToPlay (int samplesPerBlockExpected, double sampleRate)
{msg = "Call: prepareToPlay()";blockSize << samplesPerBlockExpected;sysSampleRate << sampleRate;
}void MainComponent::getNextAudioBlock (const AudioSourceChannelInfo& bufferToFill)
{bufferToFill.clearActiveBufferRegion();  //JUCE自动生成的清理缓存方法，用于避免启动音频处理时爆音Random random;for (int channel = 0; channel < bufferToFill.buffer->getNumChannels(); ++channel)//遍历需填充音频采样数据的通道{auto* buffer = bufferToFill.buffer->getWritePointer(channel, bufferToFill.startSample);//缓存块的起始点for (int sampleIndex = 0; sampleIndex < bufferToFill.numSamples; ++sampleIndex) //遍历采样点{buffer[sampleIndex] = (random.nextFloat()*2.0 - 1.0)*volume;// 写入随机采样值}}
}void MainComponent::releaseResources()
{}//==============================================================================
void MainComponent::paint (Graphics& g)
{g.setFont(30);g.setColour(Colours::red);g.drawText(msg, 10,10,300,30,Justification::left,false);g.drawText("BlockSize: "+ blockSize, 10, 40, 300, 30, Justification::left, false);g.drawText("SampleRate: "+ sysSampleRate, 10, 70, 300, 30, Justification::left, false);volumeSlider.setTextBoxStyle(Slider::TextBoxLeft,true,50,20);
}void MainComponent::resized()
{volumeSlider.setBounds(100, 100, 200, 200);
}void MainComponent::sliderValueChanged(Slider * slider)
{if (slider == &volumeSlider)volume=volumeSlider.getValue();}