JUCE学习笔记06-音频输出基础（正弦波）

JUCE学习笔记06——音频输出基础（正弦波）

知识点：

1、正弦波算法
2、波表数组

目标：

理解正弦波的算法，创建波表、Slider控制正弦波的频率与振幅

内容：

一、正弦波的基础知识

百度：正弦波是频率成分最为单一的一种信号，因这种信号的波形是数学上的正弦曲线而得名。任何复杂信号——例如音乐信号，都可以看成由许许多多频率不同、大小不等的正弦波复合而成。
更多内容：深入浅出的讲解傅里叶变换

二、正弦波的一种实现方式

通过循环读取波表数组的值填充到音频缓存区形成音频信号
1、创建所需的变量，索引为采样点，值为振幅（-1~1）。

private:Array<float> sinWT;        //存放波表的数组float wtSize;          //数组长度float phase;          //波表中采样点位置float increment;      //相邻采样点之间的位置增量float freq;           //正弦波频率float amp;           //振幅缩放（0~1）

2、prepareToPlay函数中做必要的初始化

void MainComponent::prepareToPlay (int samplesPerBlockExpected, double sampleRate)
{wtSize = 1024;        //设置波表数组的长度freq = 441;     //初始化频率；phase = 0;      //初始化采样位置amp = 0.1;        //初始化振幅缩放increment = (freq / sampleRate)*wtSize;//计算相邻采样点在波表中的位置增量//插入一个完整正弦波的振幅值（绘制波表）for (int i = 0; i < wtSize; ++i)    {sinWT.insert(i, sin(2 * float_Pi*i / wtSize));  }
}

3、在getNextAudioBlock函数中实现音频输出

void MainComponent::getNextAudioBlock (const AudioSourceChannelInfo& bufferToFill)
{bufferToFill.clearActiveBufferRegion();auto* const leftChannel = bufferToFill.buffer->getWritePointer(0, bufferToFill.startSample);//左通道缓存起始指针auto* const rightChannel = bufferToFill.buffer->getWritePointer(1, bufferToFill.startSample);//右通道缓存起始指针for (int sample = 0; sample < bufferToFill.numSamples; ++sample){leftChannel[sample] = sinWT[(int)phase]*amp; //读取波表数据写入播放缓存rightChannel[sample] = sinWT[(int)phase]*amp;    phase = fmod((phase + increment),wtSize);     //对波表采样点取模，否则采样点超出波表无法读取样本}
}

三、频率和振幅的控制

1、主组件继承Listener，创建Slider与Lable对象，设置基本属性，添加至父组件，设置显示位置

//主组件继承Listener
class MainComponent   : public AudioAppComponent,public Slider::Listener

//创建Slider与Lable对象
private://...其他代码Slider freqSlider;     //频率滑块Slider ampSlider;     //振幅滑块Label freqLabel;      //频率滑块标签Label ampLabel;         //振幅滑块标签

//设置基本属性，添加至父组件
MainComponent::MainComponent()
{//...其他代码addAndMakeVisible(freqSlider);freqSlider.setRange(50, 15000, 1);freqSlider.setValue(441);freqSlider.setTextBoxStyle(Slider::TextBoxLeft, false, 80, 20);freqSlider.setTextValueSuffix(" Hz");freqLabel.setText("Frequency", NotificationType::dontSendNotification);freqLabel.attachToComponent(&freqSlider,true);freqSlider.addListener(this); //添加监听addAndMakeVisible(ampSlider);ampSlider.setRange(0, 100, 1);ampSlider.setValue(10);ampSlider.setTextBoxStyle(Slider::TextBoxLeft, false, 80, 20);ampLabel.setText("Amplitude", NotificationType::dontSendNotification);ampLabel.attachToComponent(&ampSlider,true);ampSlider.addListener(this);//添加监听
}

void MainComponent::resized()
{freqSlider.setBounds(100, getHeight() / 3, getWidth()/3*2, getHeight() / 3);ampSlider.setBounds(100, getHeight() - getHeight() / 3, getWidth() / 3 * 2, getHeight() / 3);
}

运行效果：

2、自定义更新函数
由于prepareToPlay方法只会在setAudioChannels后调用一次，因此需要自定义一个方法（update）用于改变滑块的值时同步更新波表及振幅等，然后在getNextAudioBlock方法中调用：
创建double变量currentSampleRate用与储存采样率

double currentSampleRate;

//获取采样率存入currentSampleRate中
void MainComponent::prepareToPlay (int samplesPerBlockExpected, double sampleRate)
{//...其他代码currentSampleRate = sampleRate ;
}

//自定义更新函数

void MainComponent::update()
{freq = freqSlider.getValue();     //从滑块获取频率值；amp = ampSlider.getValue()/100;          //从滑块获取振幅缩放值increment = (freq / currentSampleRate)*wtSize;//计算相邻采样点在波表中的位置增量phase = fmod((phase + increment), wtSize);       //对波表采样点取模，否则采样点超出波表无法读取样本
}

//getNextAudioBlock（）函数中调用更新
void MainComponent::getNextAudioBlock (const AudioSourceChannelInfo& bufferToFill)
{bufferToFill.clearActiveBufferRegion();auto* const leftChannel = bufferToFill.buffer->getWritePointer(0, bufferToFill.startSample);//左通道缓存起始指针auto* const rightChannel = bufferToFill.buffer->getWritePointer(1, bufferToFill.startSample);//右通道缓存起始指针for (int sample = 0; sample < bufferToFill.numSamples; ++sample){leftChannel[sample] = sinWT[(int)phase]*amp; //读取波表数据写入播放缓存rightChannel[sample] = sinWT[(int)phase]*amp;    update();   //更新频率、振幅及相位增量等}
}

遗留问题：

1、改变滑块值时频率或振幅的变化不自然（如变化频率对应音高的变化是非线性的）
2、改变振幅时值的突然变化会产生爆音

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();//==============================================================================void prepareToPlay (int samplesPerBlockExpected, double sampleRate) override;void getNextAudioBlock (const AudioSourceChannelInfo& bufferToFill) override;void releaseResources() override;//==============================================================================void paint (Graphics& g) override;void resized() override;//==============================================================================void sliderValueChanged(Slider* slider) override;void update();private:Array<float> sinWT;       //存放波表的数组float wtSize;          //数组长度float phase;          //波表中采样点位置float increment;      //相邻采样点之间的位置增量float freq;               //正弦波频率float amp;               //振幅缩放（0~1）Slider freqSlider;     //频率滑块Slider ampSlider;     //振幅滑块Label freqLabel;      //频率滑块标签Label ampLabel;         //振幅滑块标签double currentSampleRate;JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (MainComponent)
};

//MainComponent.cpp
#include "MainComponent.h"//==============================================================================
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);}addAndMakeVisible(freqSlider);freqSlider.setRange(50, 15000, 1);freqSlider.setValue(220);freqSlider.setTextBoxStyle(Slider::TextBoxLeft, false, 80, 20);freqSlider.setTextValueSuffix(" Hz");freqLabel.setText("Frequency", NotificationType::dontSendNotification);freqLabel.attachToComponent(&freqSlider,true);freqSlider.addListener(this);addAndMakeVisible(ampSlider);ampSlider.setRange(0, 100, 1);ampSlider.setValue(10);ampSlider.setTextBoxStyle(Slider::TextBoxLeft, false, 80, 20);ampLabel.setText("Amplitude", NotificationType::dontSendNotification);ampLabel.attachToComponent(&ampSlider,true);ampSlider.addListener(this);
}MainComponent::~MainComponent()
{shutdownAudio();
}void MainComponent::update()
{freq = freqSlider.getValue();     //从滑块获取频率值；amp = ampSlider.getValue()/100;          //从滑块获取振幅缩放值increment = (freq / currentSampleRate)*wtSize;//计算相邻采样点在波表中的位置增量phase = fmod((phase + increment), wtSize);       //对波表采样点取模，否则采样点超出波表无法读取样本
}
//==============================================================================
void MainComponent::prepareToPlay (int samplesPerBlockExpected, double sampleRate)
{wtSize = 1024;        //设置波表数组的长度phase = 0;          //初始化采样位置currentSampleRate = sampleRate ;//插入一个完整正弦波的振幅值（绘制波表）for (int i = 0; i < wtSize; ++i) {sinWT.insert(i, sin(2 * float_Pi*i / wtSize));  }
}void MainComponent::getNextAudioBlock (const AudioSourceChannelInfo& bufferToFill)
{bufferToFill.clearActiveBufferRegion();auto* const leftChannel = bufferToFill.buffer->getWritePointer(0, bufferToFill.startSample);//左通道缓存起始指针auto* const rightChannel = bufferToFill.buffer->getWritePointer(1, bufferToFill.startSample);//右通道缓存起始指针for (int sample = 0; sample < bufferToFill.numSamples; ++sample){leftChannel[sample] = sinWT[(int)phase]*amp; //读取波表数据写入播放缓存rightChannel[sample] = sinWT[(int)phase]*amp;    update();   //更新频率、振幅及相位增量等}
}void MainComponent::releaseResources()
{
}//==============================================================================
void MainComponent::paint (Graphics& g)
{Rectangle<int> textArea(getWidth(), getHeight()/3);g.setColour(Colours::grey);g.drawRect(textArea, 1);g.setColour(Colours::white);g.setFont(50);g.drawText("Sinusoidal Synthesizer", textArea, Justification::centred, false);Rectangle<int> freqSliderArea(0, getHeight() / 3, getWidth(), getHeight() / 3);g.setColour(Colours::grey);g.drawRect(freqSliderArea, 1);Rectangle<int> ampSliderArea(0, getHeight() - getHeight() / 3, getWidth(), getHeight() / 3);g.setColour(Colours::grey);g.drawRect(ampSliderArea, 1);
}void MainComponent::resized()
{freqSlider.setBounds(100, getHeight() / 3, getWidth()/3*2, getHeight() / 3);ampSlider.setBounds(100, getHeight() - getHeight() / 3, getWidth() / 3 * 2, getHeight() / 3);
}void MainComponent::sliderValueChanged(Slider * slider)
{if (slider == &freqSlider)freq = freqSlider.getValue();if (slider == &ampSlider)amp = ampSlider.getValue();
}