如何从JUCE演示音频插件主机访问音频数据？

Question

我正在做一个项目，要求我从JUCE演示音频插件主机中加载的MIDI Synth插件将音频数据记录为.wav文件（每个1秒）。 基本上，我需要从MIDI Synth自动创建一个数据集（对应于不同的参数配置）。

我是否需要发送MIDI Note On / Off信息来生成音频数据？ 还是有更好的方式获取音频数据？

AudioBuffer<FloatType> getBusBuffer (AudioBuffer<FloatType>& processBlockBuffer) const

这是可以满足我需求的功能吗？ 如果是，我将如何存储数据？ 如果没有，请有人指导我正确的功能/解决方案。 谢谢。

Answer 1

我不确定您要问的是什么，所以我要猜测：

您需要以编程方式触发合成器中的一些MIDI音符，然后将所有音频写入.wav文件，对吗？

假设您已经了解JUCE，那么制作一个用于打开插件，发送MIDI和录制音频的应用程序将是微不足道的，但是调整AudioPluginHost项目可能更容易。

让我们将其分为几个简单步骤（首先打开AudioPluginHost项目）：

1. 以编程方式发送MIDI

查看GraphEditorPanel.h ，特别是GraphDocumentComponent类。 它具有一个私有成员变量： MidiKeyboardState keyState; 。 这将收集传入的MIDI消息，然后将它们插入到发送到插件的传入的音频和MIDI缓冲区中。

您可以简单地调用keyState.noteOn (midiChannel, midiNoteNumber, velocity)和keyState.noteOff (midiChannel, midiNoteNumber, velocity)来触发音符。

2. 记录音频输出

在JUCE中这是一件非常简单的事情-您应该先查看JUCE演示。 下面的示例在后台记录输出音频，但是还有许多其他方法可以执行此操作：

class AudioRecorder  : public AudioIODeviceCallback
{
public:
    AudioRecorder (AudioThumbnail& thumbnailToUpdate)
        : thumbnail (thumbnailToUpdate)
    {
        backgroundThread.startThread();
    }

    ~AudioRecorder()
    {
        stop();
    }

    //==============================================================================
    void startRecording (const File& file)
    {
        stop();

        if (sampleRate > 0)
        {
            // Create an OutputStream to write to our destination file...
            file.deleteFile();
            ScopedPointer<FileOutputStream> fileStream (file.createOutputStream());

            if (fileStream.get() != nullptr)
            {
                // Now create a WAV writer object that writes to our output stream...
                WavAudioFormat wavFormat;
                auto* writer = wavFormat.createWriterFor (fileStream.get(), sampleRate, 1, 16, {}, 0);

                if (writer != nullptr)
                {
                    fileStream.release(); // (passes responsibility for deleting the stream to the writer object that is now using it)

                    // Now we'll create one of these helper objects which will act as a FIFO buffer, and will
                    // write the data to disk on our background thread.
                    threadedWriter.reset (new AudioFormatWriter::ThreadedWriter (writer, backgroundThread, 32768));

                    // Reset our recording thumbnail
                    thumbnail.reset (writer->getNumChannels(), writer->getSampleRate());
                    nextSampleNum = 0;

                    // And now, swap over our active writer pointer so that the audio callback will start using it..
                    const ScopedLock sl (writerLock);
                    activeWriter = threadedWriter.get();
                }
            }
        }
    }

    void stop()
    {
        // First, clear this pointer to stop the audio callback from using our writer object..
        {
            const ScopedLock sl (writerLock);
            activeWriter = nullptr;
        }

        // Now we can delete the writer object. It's done in this order because the deletion could
        // take a little time while remaining data gets flushed to disk, so it's best to avoid blocking
        // the audio callback while this happens.
        threadedWriter.reset();
    }

    bool isRecording() const
    {
        return activeWriter != nullptr;
    }

    //==============================================================================
    void audioDeviceAboutToStart (AudioIODevice* device) override
    {
        sampleRate = device->getCurrentSampleRate();
    }

    void audioDeviceStopped() override
    {
        sampleRate = 0;
    }

    void audioDeviceIOCallback (const float** inputChannelData, int numInputChannels,
                                float** outputChannelData, int numOutputChannels,
                                int numSamples) override
    {
        const ScopedLock sl (writerLock);

        if (activeWriter != nullptr && numInputChannels >= thumbnail.getNumChannels())
        {
            activeWriter->write (inputChannelData, numSamples);

            // Create an AudioBuffer to wrap our incoming data, note that this does no allocations or copies, it simply references our input data
            AudioBuffer<float> buffer (const_cast<float**> (inputChannelData), thumbnail.getNumChannels(), numSamples);
            thumbnail.addBlock (nextSampleNum, buffer, 0, numSamples);
            nextSampleNum += numSamples;
        }

        // We need to clear the output buffers, in case they're full of junk..
        for (int i = 0; i < numOutputChannels; ++i)
            if (outputChannelData[i] != nullptr)
                FloatVectorOperations::clear (outputChannelData[i], numSamples);
    }

private:
    AudioThumbnail& thumbnail;
    TimeSliceThread backgroundThread  { "Audio Recorder Thread" }; // the thread that will write our audio data to disk
    ScopedPointer<AudioFormatWriter::ThreadedWriter> threadedWriter; // the FIFO used to buffer the incoming data
    double sampleRate   = 0.0;
    int64 nextSampleNum = 0;

    CriticalSection writerLock;
    AudioFormatWriter::ThreadedWriter* volatile activeWriter = nullptr;
};

请注意，包含来自插件的音频数据的实际音频回调发生在FilterGraph的AudioProcessorGraph内部。 每秒有多次音频回调发生，原始音频数据被传入。在AudioPluginHost内更改此设置可能很麻烦，除非您知道自己在做什么–使用上面的示例可能会更简单或创建自己的具有自己音频流的应用。

您询问的功能：

AudioBuffer<FloatType> getBusBuffer (AudioBuffer<FloatType>& processBlockBuffer) const

是无关紧要的。 一旦您已经进入音频回调，这将使您将音频发送到插件的总线（又名，如果您的合成器具有侧链）。 相反，您要做的是从回调中获取音频，并将其传递给AudioFormatWriter ，或者最好传递给AudioFormatWriter::ThreadedWriter以便实际写入发生在不同的线程上。

如果您完全不熟悉C ++或JUCE，则Max / MSP或Pure Data可能会更容易使您快速掌握一些东西。