使用 NAudio 一次播放多个 wav 文件时的音质问题

Question

My objective is this: to allow users of my .NET program to choose their own.wav files for sound effects. These effects may be played simultaneously. NAudio seemed like my best bet.

I decided to use WaveMixerStream32. One early challenge was that my users had.wav files of different formats, so to be able to mix them together with WaveMixerStream32, I needed to "normalize" them to a common format. I wasn't able to find a good example of this to follow so I suspect my problem is a result of my doing this part wrong.

My problem is that when some sounds are played, there are very noticeable "clicking" sounds at their end. I can reproduce this myself.

Also, my users have complained that sometimes, sounds aren't played at all, or are "scratchy" all the way through. I haven't been able to reproduce this in development but I have heard this for myself in our production environment.

I've played the user's wav files myself using Windows Media and VLC, so I know the files aren't corrupt. It must be a problem with how I'm using them with NAudio.

My NAudio version is v1.4.0.0.

Here's the code I used. To set up the mixer:

_mixer = new WaveMixerStream32 { AutoStop = false, };
_waveOutDevice = new WaveOut(WaveCallbackInfo.NewWindow())
{
    DeviceNumber = -1,
    DesiredLatency = 300,
    NumberOfBuffers = 3,
};
_waveOutDevice.Init(_mixer);
_waveOutDevice.Play();

Surprisingly, if I set "NumberOfBuffers" to 2 here I found that sound quality was awful, with audible "ticks" occurring several times a second.

To initialize a sound file, I did this:

var sample = new AudioSample(fileName);
sample.Position = sample.Length; // To prevent the sample from playing right away
_mixer.AddInputStream(sample);

AudioSample is my class. Its constructor is responsible for the "normalization" of the wav file format. It looks like this:

private class AudioSample : WaveStream
{
private readonly WaveChannel32 _channelStream;
public AudioSample(string fileName)
{
    MemoryStream memStream;
    using (var fileStream = File.OpenRead(fileName))
    {
        memStream = new MemoryStream();
        memStream.SetLength(fileStream.Length);
        fileStream.Read(memStream.GetBuffer(), 0, (int)fileStream.Length);
    }
    WaveStream originalStream = new WaveFileReader(memStream);
    var pcmStream = WaveFormatConversionStream.CreatePcmStream(originalStream);
    var blockAlignReductionStream = new BlockAlignReductionStream(pcmStream);
    var waveFormatConversionStream = new WaveFormatConversionStream(
        new WaveFormat(44100, blockAlignReductionStream.WaveFormat.BitsPerSample, 2), blockAlignReductionStream);
    var waveOffsetStream = new WaveOffsetStream(waveFormatConversionStream);
    _channelStream = new WaveChannel32(waveOffsetStream);
}

Basically, the AudioSample delegates to its _channelStream object. To play an AudioSample, my code sets its "Position" to 0. This code that does this is marshalled onto the UI thread.

This almost works great. I can play multiple sounds simultaneously. Unfortunately the sound quality is bad as described above. Can anyone help me figure out why?

Answer 1

Some points in response to your question:

• Yes, you have to have all inputs at the same sample rate before you feed them into a mixer. This is simply how digital audio works. The ACM sample rate conversion provided by WaveFormatConversion stream isn't brilliant (has no aliasing protection). What sample rates are your input files typically at?
• You are passing every input through two WaveFormatConversionStreams. Only do this if it is absolutely necessary.
• I'm surprised that you are getting bad sound with NumberOfBuffers=2, which is now the default in NAudio. Have you been pausing and resuming, because there was a bug where a buffer could get dropped (fixed in the latest and will be fixed for NAudio 1.4 final)
• A click at the end of a file can just mean it doesn't end on a zero sample. You would have to add a fade out to eliminate this (a lot of media players do this automatically)
• Whenever you are troubleshooting a bad sound issue, I always recommend using WaveFileWriter to convert your WaveStream into a WAV file (taking care not to produce a never ending file,). so you can listen to it in another media player, This allows you to quickly determine whether it is your audio processing that is causing the problem. or the playback itself.