c# - How to record and playback with NAudio using AsioOut

Question

I'm trying to get the sound input and send output directly with less latency possible with C#.

I'm using the library NAudio that supports ASIO for better latency.

In particular, I use the AsioOut object for recording and another for playback initialized with a BufferedWaveProvider, which is filled in a Callback function: OnAudioAvailable, which allows me to use the ASIO buffers.

The problem is that I hear the sound with various glitches and with a bit of delay. I think the problem is in the function OnAudioAvailable where the buffer is filled with data taken as input from the sound card.

Declarations:

NAudio.Wave.AsioOut playAsio;
NAudio.Wave.AsioOut recAsio;
NAudio.Wave.BufferedWaveProvider buffer;

Play procedure:

if (sourceList.SelectedItems.Count == 0) return;

int deviceNumber = sourceList.SelectedItems[0].Index;

recAsio = new NAudio.Wave.AsioOut(deviceNumber);
recAsio.InitRecordAndPlayback(null, 2, 44100); //rec channel = 1

NAudio.Wave.WaveFormat formato = new NAudio.Wave.WaveFormat();
buffer = new NAudio.Wave.BufferedWaveProvider(formato);

recAsio.AudioAvailable += new EventHandler<NAudio.Wave.AsioAudioAvailableEventArgs>(OnAudioAvailable);

//Collego l'output col buffer
playAsio = new NAudio.Wave.AsioOut(deviceNumber);
playAsio.Init(buffer);

//Registro
recAsio.Play();
//Playback
playAsio.Play();

OnAudioAvailable():

//Callback
private unsafe void OnAudioAvailable(object sender, NAudio.Wave.AsioAudioAvailableEventArgs e)
{
    //Copio tutti gli elementi di InputBuffers in buf e li aggiungo in coda al buffer
    byte[] buf = new byte[e.SamplesPerBuffer];
    for (int i = 0; i < e.InputBuffers.Length; i++)
    {
        Marshal.Copy(e.InputBuffers[i], buf, 0, e.SamplesPerBuffer);
        //Aggiungo in coda al buffer
        buffer.AddSamples(buf, 0, buf.Length);
    }
}

AsioAudioAvailableEventArgs definition:

public AsioAudioAvailableEventArgs(IntPtr[] inputBuffers, int samplesPerBuffer, AsioSampleType asioSampleType);
public float[] GetAsInterleavedSamples();

Does anyone know how to fix it? Thank you all.

Answer 1

You should not be using two instances of AsioOut for the same device. I'm surprised this works at all. Just use the one, with InitRecordAndPlayback.

For absolute minimal latency for pass-through monitoring, in AudioAvailableEvent, copy directly to the OutputBuffers, and set WrittenToOutputBuffers = true. This means you don't need a BufferedWaveProvider.

Also remember that any glitches are simply due to you not managing to process the AudioAvailable event quickly enough. When you're working with ASIO, you can be at very low latencies (e.g. sub 10ms), and can be dealing with lots of data (e.g. 96kHz sample rates, 8 channels of input and output). So you need to do a lot of moving of data in a short time window. With .NET, you have to factor in the unfortunate fact that the garbage collector could kick in at any time and cause you to miss a buffer from time to time.