Question

我正在开发一个项目，要求我将音频数据录制为.jav文件（每个1秒）从JUCE演示音频插件主机中加载的MIDI Synth插件。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）。

我是否必须发送MIDI Note On / Off消息才能生成音频数据？或者有更好的方法来获取音频数据吗？

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

这是解决我需求的功能吗？如果是，我将如何存储数据？如果没有，有人可以指导我找到合适的功能/解决方案。谢谢。

Answer 1

我不确定你在问什么，所以我猜：

您需要以编程方式触发合成器中的某些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，那么创建一个打开插件，发送MIDI和录制音频的应用程序是相当简单的，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，特别是班级GraphDocumentComponent。它有一个私有成员变量：MidiKeyboardState keyState;。这会收集传入的MIDI信息，然后将它们插入到传入的音频和信号中。发送到插件的MIDI缓冲区。

您只需致电keyState.noteOn (midiChannel, midiNoteNumber, velocity)和keyState.noteOff (midiChannel, midiNoteNumber, velocity)即可触发记事。

录制音频输出

在JUCE中这是一个相当简单的事情 - 你应该从看看JUCE演示开始。以下示例在后台记录输出音频，但还有很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，包含插件音频数据的实际音频回调发生在AudioProcessorGraph内的FilterGraph内。原始音频数据传入时会发生多次音频回调。除非你知道你在做什么，否则在AudioPluginHost内更改它可能会非常麻烦 - 使用它可能会更简单像上面的例子或创建自己的应用程序，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。一旦你已经进入音频回调，这将使你的音频被发送到你的插件的总线（如果你的合成器有一个侧链）。你要做的是取出来自回调的音频并将其传递给AudioFormatWriter，或者最好是AudioFormatWriter::ThreadedWriter，以便实际写作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提升。

如何从JUCE演示音频插件主机访问音频数据？

1 个答案: