如何从 JUCE Demo Audio Plugin Host 访问音频数据？

Question

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

我是否必须发送 MIDI 音符 On/Off 消息才能生成音频数据？或者有没有更好的获取音频数据的方法？

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

这个功能能解决我的需求吗？如果是，我将如何存储数据？如果没有，请有人引导我向右function/solution。谢谢。

Answer 1

我不太确定你在问什么，所以我猜：

您需要在合成器中以编程方式触发一些 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，制作一个打开您的插件、发送 MIDI 和录制音频的应用程序将是相当简单的，但调整 AudioPluginHost 项目可能更容易。

让我们把它分成几个简单的步骤（首先打开 AudioPluginHost 项目）：

以编程方式发送 MIDI

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

您只需调用 keyState.noteOn (midiChannel, midiNoteNumber, velocity) 和 keyState.noteOff (midiChannel, midiNoteNumber, velocity) 即可触发注释。

录制音频输出

在 JUCE 中这是一件相当简单的事情 — 您应该从查看 JUCE 演示开始。以下示例在后台录制输出音频，但还有很多其他方法可以做到这一点：

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，包含插件音频数据的实际音频回调发生在 FilterGraph 内的 AudioProcessorGraph 内。传入原始音频数据时，每秒会发生多次音频回调。除非您知道自己在做什么，否则在 AudioPluginHost 内更改它可能会非常混乱——使用某些东西可能会更简单就像上面的例子一样，或者创建你自己的应用程序，它有自己的音频流。

您询问的功能：

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

无关紧要。一旦你已经在音频回调中，这将使你的音频被发送到你的插件的总线（如果你的合成器有侧链）。您要做的是从回调中获取音频并将其传递给 AudioFormatWriter，或者最好是 AudioFormatWriter::ThreadedWriter，以便实际写入发生在不同的线程上。

如果您对 C++ 或 JUCE 一点都不熟悉，Max/MSP 或 Pure Data 可能更容易让您快速做出一些东西。

如何从 JUCE Demo Audio Plugin Host 访问音频数据？

How to access Audio data from JUCE Demo Audio Plugin Host?

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