淡入/淡出声音 [英] Fading sound in/out

问题描述

我的背景音乐不断循环播放.我希望它在用户确实按下按钮时淡出.

I have a background sound playing in an endless loop. I want it to fade out when the user does press a button.

我尝试了以下操作:

• 使用WaveStream启动DirectSoundOut
• 计时器更改WaveChannel32的音量.

问题:

• 在播放声音时更改音量会产生噪音.

有人知道更好的解决方案吗?

Does anyone knows a better solution?

推荐答案

要执行平滑的淡入或淡出，您需要在样本级别执行此操作.然后，将每个样本乘以逐渐增加或减少的数字.您正在使用WaveChannel32，所以您的音频已经转换为32位浮点型.然后，我将创建另一个IWaveProvider实现程序，该实现程序负责执行淡入和淡出操作.通常，它会不变地通过样本，但是在Read方法中，如果您处于淡入或淡出状态，它将乘以每个样本(如果是立体声，则成对).

To perform a smooth fade-in or fade-out, you need to do so at the sample level. You then multiply each sample by a gradually increasing or decreasing number. You are using WaveChannel32, so your audio has already been converted to 32 bit float. I would then create another IWaveProvider implementer that was responsible for doing the fade in and fade out. Normally it would pass through samples unchanged, but in the Read method, if you are in a fade in or fade out, it would multiply each sample (or pair if it is stereo).

NAudio 1.5中的ISampleProvider接口旨在简化此类操作，因为它允许您以32位浮点数形式处理样本，而不是实现IWaveProvider，后者需要您将byte []转换为float [ ].这是我刚刚制作的用于淡入和淡出的SampleProvider，它将包含在下一个NAudio中，并希望很快能在此博客中找到.只需以适当的淡入时间调用BeginFadeIn或BeginFadeOut.

The ISampleProvider interface in NAudio 1.5 was designed to make this type of thing much easier, as it allows you to deal samples already as 32 bit floats, rather than implementing IWaveProvider which requires you to convert from a byte[] to float[]. Here's a SampleProvider for fade-in and fade-out I just made which I will include in the next NAudio, and hopefully blog about it soon. Just call BeginFadeIn or BeginFadeOut with the appropriate fade duration.

public class FadeInOutSampleProvider : ISampleProvider
{
    enum FadeState
    {
        Silence,
        FadingIn,
        FullVolume,
        FadingOut,
    }

    private readonly object lockObject = new object();
    private readonly ISampleProvider source;
    private int fadeSamplePosition;
    private int fadeSampleCount;
    private FadeState fadeState;

    public FadeInOutSampleProvider(ISampleProvider source)
    {
        this.source = source;
        this.fadeState = FadeState.FullVolume;
    }

    public void BeginFadeIn(double fadeDurationInMilliseconds)
    {
        lock (lockObject)
        { 
            fadeSamplePosition = 0;
            fadeSampleCount = (int)((fadeDurationInMilliseconds * source.WaveFormat.SampleRate) / 1000);
            fadeState = FadeState.FadingIn;
        }
    }

    public void BeginFadeOut(double fadeDurationInMilliseconds)
    {
        lock (lockObject)
        {
            fadeSamplePosition = 0;
            fadeSampleCount = (int)((fadeDurationInMilliseconds * source.WaveFormat.SampleRate) / 1000);
            fadeState = FadeState.FadingOut;
        }
    }

    public int Read(float[] buffer, int offset, int count)
    {
        int sourceSamplesRead = source.Read(buffer, offset, count);
        lock (lockObject)
        {
            if (fadeState == FadeState.FadingIn)
            {
                FadeIn(buffer, offset, sourceSamplesRead);
            }
            else if (fadeState == FadeState.FadingOut)
            {
                FadeOut(buffer, offset, sourceSamplesRead);
            }
            else if (fadeState == FadeState.Silence)
            {
                ClearBuffer(buffer, offset, count);
            }
        }
        return sourceSamplesRead;
    }

    private static void ClearBuffer(float[] buffer, int offset, int count)
    {
        for (int n = 0; n < count; n++)
        {
            buffer[n + offset] = 0;
        }
    }

    private void FadeOut(float[] buffer, int offset, int sourceSamplesRead)
    {
        int sample = 0;
        while (sample < sourceSamplesRead)
        {
            float multiplier = 1.0f - (fadeSamplePosition / (float)fadeSampleCount);
            for (int ch = 0; ch < source.WaveFormat.Channels; ch++)
            {
                buffer[offset + sample++] *= multiplier;
            }
            fadeSamplePosition++;
            if (fadeSamplePosition > fadeSampleCount)
            {
                fadeState = FadeState.Silence;
                // clear out the end
                ClearBuffer(buffer, sample + offset, sourceSamplesRead - sample);
                break;
            }
        }
    }

    private void FadeIn(float[] buffer, int offset, int sourceSamplesRead)
    {
        int sample = 0;
        while (sample < sourceSamplesRead)
        {
            float multiplier = (fadeSamplePosition / (float)fadeSampleCount);
            for (int ch = 0; ch < source.WaveFormat.Channels; ch++)
            {
                buffer[offset + sample++] *= multiplier;
            }
            fadeSamplePosition++;
            if (fadeSamplePosition > fadeSampleCount)
            {
                fadeState = FadeState.FullVolume;
                // no need to multiply any more
                break;
            }
        }
    }

    public WaveFormat WaveFormat
    {
        get { return source.WaveFormat; }
    }
}

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