unity - 正弦波振荡器产生金属噪音答案

【问题标题】：Unity - sine wave oscillator generates metallic noiseunity - 正弦波振荡器产生金属噪音
【发布时间】：2020-05-03 23:02:01
【问题描述】：

我正在尝试创建一个正弦波振荡器来播放音频源。

起初我创建了一个这样的简单的：

public class FirstOscillator : MonoBehaviour
{
    public double frequency = 400.0;

    private double increment;
    private double phase;
    private double sampleRate = 48000.0;

    public float gain;

    void OnAudioFilterRead(float[] data, int channels)
    {
        increment = frequency * 2.0 * Mathf.PI / sampleRate;
        for (int i = 0; i < data.Length; i += channels)
        {
            phase += increment;
            data[i] = (float) (gain * Mathf.Sin((float) phase));

            if (channels == 2)
            {
                data[i + 1] = data[i];
            }
        }
    }
}

这工作得很好，并产生了一个很好的正弦波。

但我认为在设计方面，我的振荡器最好是 amplitude(frequency, time) 的某种函数，所以我试图修改它以实际使用时间并将振荡提取到一个方法中：

public class SecondOscillator : MonoBehaviour, IAudioFilter
{
    public double frequency = 400.0;

    private double sampleRate = 48000.0;

    public float gain;

    public void OnAudioFilterRead(float[] data, int channels)
    {
        var time = AudioSettings.dspTime;

        for (int i = 0; i < data.Length; i += channels)
        {
            data[i] = gain * Amplitude((float)frequency, (float)(time + i / sampleRate / channels));

            if (channels == 2)
            {
                data[i + 1] = data[i];
            }

        }
    }

    private float Amplitude(float freq, float time)
    {
        return Mathf.Sin(freq * time * 2 * Mathf.PI);
    }
}

由于某种原因，这会产生听起来很奇怪的金属噪音，但它会对频率变化做出反应。我想知道可能是什么问题。

更新

在 cmets 部分，人们建议 AudioSettings.dspTime 是样本数，而不是以秒为单位的时间。我认为情况并非如此，所以我编写了一个快速脚本来测试它：

class SampleRateTest : MonoBehaviour
{
    public int sampleRate;

    public void Awake()
    {
        sampleRate = AudioSettings.outputSampleRate;
    }

    private StringBuilder sb = new StringBuilder();

    private int samplesTakenStart = 5;
    private int samplesTakenEnd = 5;

    private int loggedFrames = 5;
    private int loggedFrameIndex = 0;

    public void OnAudioFilterRead(float[] data, int channels)
    {
        var time = AudioSettings.dspTime;
        for (var index = 0; index < data.Length; index++)
        {
            if (index < samplesTakenStart || index > data.Length - samplesTakenEnd)
                sb.AppendLine($"Sample {index} time is {time}");
            else if (index == samplesTakenStart)
                sb.AppendLine("...");

            time += 1.0 / sampleRate / channels;
        }

        sb.AppendLine("End of frame " + loggedFrameIndex);

        if (loggedFrameIndex++ == loggedFrames)
            Debug.Log(sb.ToString());
    }

}

这会产生以下输出：

Sample 0 time is 1196.144
Sample 1 time is 1196.14401041667
Sample 2 time is 1196.14402083333
Sample 3 time is 1196.14403125
Sample 4 time is 1196.14404166667
...
Sample 508 time is 1196.14929166661
Sample 509 time is 1196.14930208328
Sample 510 time is 1196.14931249994
Sample 511 time is 1196.14932291661
End of frame 0
Sample 0 time is 1196.14933333333
Sample 1 time is 1196.14934375
Sample 2 time is 1196.14935416667
Sample 3 time is 1196.14936458333
Sample 4 time is 1196.149375
...
Sample 508 time is 1196.15462499994
Sample 509 time is 1196.15463541661
Sample 510 time is 1196.15464583328
Sample 511 time is 1196.15465624994
End of frame 1
Sample 0 time is 1196.15466666667
Sample 1 time is 1196.15467708333
Sample 2 time is 1196.1546875
Sample 3 time is 1196.15469791667
Sample 4 time is 1196.15470833333
...
Sample 508 time is 1196.15995833328
Sample 509 time is 1196.15996874994
Sample 510 time is 1196.15997916661
Sample 511 time is 1196.15998958328
End of frame 2
Sample 0 time is 1196.16
Sample 1 time is 1196.16001041667
Sample 2 time is 1196.16002083333
Sample 3 time is 1196.16003125
Sample 4 time is 1196.16004166667
...
Sample 508 time is 1196.16529166661
Sample 509 time is 1196.16530208328
Sample 510 time is 1196.16531249994
Sample 511 time is 1196.16532291661
End of frame 3
Sample 0 time is 1196.16533333333
Sample 1 time is 1196.16534375
Sample 2 time is 1196.16535416667
Sample 3 time is 1196.16536458333
Sample 4 time is 1196.165375
...
Sample 508 time is 1196.17062499994
Sample 509 time is 1196.17063541661
Sample 510 time is 1196.17064583328
Sample 511 time is 1196.17065624994
End of frame 4
Sample 0 time is 1196.17066666667
Sample 1 time is 1196.17067708333
Sample 2 time is 1196.1706875
Sample 3 time is 1196.17069791667
Sample 4 time is 1196.17070833333
...
Sample 508 time is 1196.17595833328
Sample 509 time is 1196.17596874994
Sample 510 time is 1196.17597916661
Sample 511 time is 1196.17598958328
End of frame 5

所以在我看来AudioSettings.dspTime 确实是时间，所以它不应该除以sampleRate。如果重要的话，我系统上的channels 计数是 2。

更新 2： 我还尝试删除特定于通道的代码并将项目音频设置设置为单声道（而不是立体声），但这没有帮助，所以我认为通道不是这里的问题。

另外，I created a wav demo of the sound I get。对我来说，这听起来更像是正方形而不是正弦。

【问题讨论】：

我的猜测是我以某种错误的方式使用AudioSettings.dspTime，因为我真的不知道它在OnAudioFilterRead 调用之间是如何变化的，但如果是这样的话——正确的方法是什么使用它？
DSP 时间应该只是一些样本。因此，据我所知，time + i / sampleRate 作为Amplitude 的参数将无法正常运行
(float)( (time + i) / sampleRate) 应该是您正在寻找的。我很想看看AudioSettings.dspTime 是否在每次调用OnAudioFilterRead 时进步data.Length。这可能值得验证。

标签： c# unity3d audio signal-processing procedural-music

【解决方案1】：

哦。我的。上帝。问题是我使用的是float 值而不是double，看起来浮点计算对于这类数据来说不够精确。将我所有的花车都改为双打，现在可以使用了。

【讨论】：