通过XAudio2播放窦 [英] Playing sinus through XAudio2

问题描述

我使用XAudio2作出音频播放器。我们在640字节的数据包流的数据，在8000Hz的采样率和16个字节的样本深度。我们正在使用SlimDX访问XAudio2。

I'm making an audio player using XAudio2. We are streaming data in packets of 640 bytes, at a sample rate of 8000Hz and sample depth of 16 bytes. We are using SlimDX to access XAudio2.

但播放声音时，我们注意到，音质差。此，例如，是一个3kHz的正弦曲线，以Audacity的捕获。

But when playing sound, we are noticing that the sound quality is bad. This, for example, is a 3KHz sine curve, captured with Audacity.

我都凝结着音频播放器的裸基础知识，但音质还是不错。这是XAudio2，SlimDX，还是我的code错误，或者这只是当一个为8kHz到44.1时出现的神器？最后一个似乎是不合理，因为我们也产生由Windows媒体播放器完美发挥PCM WAV文件。

I have condensed the audio player to the bare basics, but the audio quality is still bad. Is this a bug in XAudio2, SlimDX, or my code, or is this simply an artifact that occurs when one go from 8KHz to 44.1KHz? The last one seems unreasonable, as we also generate PCM wav files which are played perfectly by Windows Media Player.

以下是基本实现，其产生破碎的正弦

The following is the basic implementation, which generates the broken Sine.

public partial class MainWindow : Window
{
    private XAudio2 device = new XAudio2();
    private WaveFormatExtensible format = new WaveFormatExtensible();
    private SourceVoice sourceVoice = null;
    private MasteringVoice masteringVoice = null;
    private Guid KSDATAFORMAT_SUBTYPE_PCM = new Guid("00000001-0000-0010-8000-00aa00389b71");
    private AutoResetEvent BufferReady = new AutoResetEvent(false);

    private PlayBufferPool PlayBuffers = new PlayBufferPool();

    public MainWindow()
    {
        InitializeComponent();

        Closing += OnClosing;

        format.Channels = 1;
        format.BitsPerSample = 16;
        format.FormatTag = WaveFormatTag.Extensible;
        format.BlockAlignment = (short)(format.Channels * (format.BitsPerSample / 8));
        format.SamplesPerSecond = 8000;
        format.AverageBytesPerSecond = format.SamplesPerSecond * format.BlockAlignment;
        format.SubFormat = KSDATAFORMAT_SUBTYPE_PCM;
    }

    private void OnClosing(object sender, CancelEventArgs cancelEventArgs)
    {
        sourceVoice.Stop();
        sourceVoice.Dispose();
        masteringVoice.Dispose();

        PlayBuffers.Dispose();
    }

    private void button_Click(object sender, RoutedEventArgs e)
    {
        masteringVoice = new MasteringVoice(device);

        PlayBuffer buffer = PlayBuffers.NextBuffer();

        GenerateSine(buffer.Buffer);
        buffer.AudioBuffer.AudioBytes = 640;

        sourceVoice = new SourceVoice(device, format, VoiceFlags.None, 8);
        sourceVoice.BufferStart += new EventHandler<ContextEventArgs>(sourceVoice_BufferStart);
        sourceVoice.BufferEnd += new EventHandler<ContextEventArgs>(sourceVoice_BufferEnd);

        sourceVoice.SubmitSourceBuffer(buffer.AudioBuffer);

        sourceVoice.Start();
    }

    private void sourceVoice_BufferEnd(object sender, ContextEventArgs e)
    {
        BufferReady.Set();
    }

    private void sourceVoice_BufferStart(object sender, ContextEventArgs e)
    {
        BufferReady.WaitOne(1000);

        PlayBuffer nextBuffer = PlayBuffers.NextBuffer();
        nextBuffer.DataStream.Position = 0;
        nextBuffer.AudioBuffer.AudioBytes = 640;
        GenerateSine(nextBuffer.Buffer);

        Result r = sourceVoice.SubmitSourceBuffer(nextBuffer.AudioBuffer);
    }

    private void GenerateSine(byte[] buffer)
    {
        double sampleRate = 8000.0;
        double amplitude = 0.25 * short.MaxValue;
        double frequency = 3000.0;
        for (int n = 0; n < buffer.Length / 2; n++)
        {
            short[] s = { (short)(amplitude * Math.Sin((2 * Math.PI * n * frequency) / sampleRate)) };
            Buffer.BlockCopy(s, 0, buffer, n * 2, 2);
        }
    }
}

public class PlayBuffer : IDisposable
{
    #region Private variables
    private IntPtr BufferPtr;
    private GCHandle BufferHandle;
    #endregion

    #region Constructors
    public PlayBuffer()
    {
        Index = 0;
        Buffer = new byte[640 * 4]; // 640 = 30ms
        BufferHandle = GCHandle.Alloc(this.Buffer, GCHandleType.Pinned);
        BufferPtr = new IntPtr(BufferHandle.AddrOfPinnedObject().ToInt32());

        DataStream = new DataStream(BufferPtr, 640 * 4, true, false);
        AudioBuffer = new AudioBuffer();
        AudioBuffer.AudioData = DataStream;
    }

    public PlayBuffer(int index)
        : this()
    {
        Index = index;
    }
    #endregion

    #region Destructor
    ~PlayBuffer()
    {
        Dispose();
    }
    #endregion

    #region Properties
    protected int Index { get; private set; }
    public byte[] Buffer { get; private set; }
    public DataStream DataStream { get; private set; }
    public AudioBuffer AudioBuffer { get; private set; }
    #endregion

    #region Public functions
    public void Dispose()
    {
        if (AudioBuffer != null)
        {
            AudioBuffer.Dispose();
            AudioBuffer = null;
        }

        if (DataStream != null)
        {
            DataStream.Dispose();
            DataStream = null;
        }
    }
    #endregion
}

public class PlayBufferPool : IDisposable
{
    #region Private variables
    private int _currentIndex = -1;
    private PlayBuffer[] _buffers = new PlayBuffer[2];
    #endregion

    #region Constructors
    public PlayBufferPool()
    {
        for (int i = 0; i < 2; i++)
            Buffers[i] = new PlayBuffer(i);
    }
    #endregion

    #region Desctructor
    ~PlayBufferPool()
    {
        Dispose();
    }
    #endregion

    #region Properties
    protected int CurrentIndex
    {
        get { return _currentIndex; }
        set { _currentIndex = value; }
    }

    protected PlayBuffer[] Buffers
    {
        get { return _buffers; }
        set { _buffers = value; }
    }
    #endregion

    #region Public functions
    public void Dispose()
    {
        for (int i = 0; i < Buffers.Length; i++)
        {
            if (Buffers[i] == null)
                continue;

            Buffers[i].Dispose();
            Buffers[i] = null;
        }
    }

    public PlayBuffer NextBuffer()
    {
        CurrentIndex = (CurrentIndex + 1) % Buffers.Length;
        return Buffers[CurrentIndex];
    }
    #endregion
}

一些额外的细节：

Some extra details:

这是用来回放录制的声音与不同的COM pression如ALAW，μLAW或TRUESPEECH。该数据在小数据包发送，德$ C $光盘，发送到这个播放器。这就是为什么我们使用如此低采样率，因此小缓冲区的原因。
有与我们的数据没有问题，但是，由于产生与在由WMP或VLC完美重放数据结果WAV文件

This is used to replay recorded voice with various compression such as ALAW, µLAW or TrueSpeech. The data is sent in small packets, decoded and sent to this player. This is the reason for why we're using so low sampling rate, and so small buffers. There are no problems with our data, however, as generating a WAV file with the data results in perfect replay by WMP or VLC.

编辑：在n音讯重写球员，我们现在已经解决这一点。
我仍然有兴趣在任何输入，以这里发生了什么。它是我们在PlayBuffers的做法，或者是它只是在DirectX中的错误/限制，还是包装？我尝试使用，而不是SlimDX SharpDX，但这并没有改变结果什么。

edit: We have now "solved" this by rewriting the player in NAudio. I'd still be interested in any input as to what is happening here. Is it our approach in the PlayBuffers, or is it simply a bug/limitation in DirectX, or the wrappers? I tried using SharpDX instead of SlimDX, but that did not change the result anything.

推荐答案

这看起来好像是采样没有正确的抗锯齿（重建）滤波器完成。截止频率是太高（原高于奈奎斯特频率），因此很多别名正在preserved，导致类似的输出在8000赫兹采取的样本之间分段线性插值。

It looks as if the upsampling is done without a proper anti-aliasing (reconstruction) filter. The cutoff frequency is far too high (above the original Nyquist frequency) and therefore a lot of the aliases are being preserved, resulting in output resembling piecewise-linear interpolation between the samples taken at 8000 Hz.

尽管所有的不同的选择正在做8kHz至44.1，其中，他们这样做是很重要的方式，即一个库是否良好的一个事实是变频没有证据表明上转换是不是错误的源其他。

Although all your different options are doing an upconversion from 8kHz to 44.1kHz, the way in which they do that is important, and the fact that one library does it well is no proof that the upconversion is not the source of error in the other.

这篇关于通过XAudio2播放窦的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！