NAudioで信号処理 (その９)

NAudioで信号処理 (目次) - Hope is a Dream. Dream is a Hope.

NAudioで信号処理 (その９)

エフェクト処理 Part3 (Echo!!!!)

C# Audio Tutorial 9 - EffectStream Part 3 (Echo!)

やっとエフェクトの処理を実装します！

Echo.cs

先ほど作ったIEffect.csインターフェイスを実装したEcho.csを作ります。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Tutorial
{
    public class Echo : IEffect
    {

        public int EchoLength { get; private set; }
        public float EchoFactor { get; set; }

        private Queue<float> samples;

        public Echo(int length = 20000, float factor = 0.5f)
        {
            this.EchoLength = length;
            this.EchoFactor = factor;
            this.samples = new Queue<float>();

            for (int i = 0; i < length; i++) samples.Enqueue(0f);
        }

        float IEffect.ApplyEffect(float sample)
        {
            samples.Enqueue(sample); // add que
            return sample + EchoFactor * samples.Dequeue();

        }
    }
}

EffectStream.cs

using System;
using System.Collections.Generic;
using NAudio.Wave;

namespace Tutorial
{
    public class EffectStream : WaveStream
    {
        public WaveStream SourceStream { get; set; }

        public List<IEffect> Effects { get; set; }

        public EffectStream(WaveStream stream)
        {
            this.SourceStream = stream;
            this.Effects = new List<IEffect>();
        }


        //... 省略


        private int channel = 0;

        public override int Read(byte[] buffer, int offset, int count)
        {
            //*****************************************************************//
            // ここで信号処理をする
            //*****************************************************************//
            Console.WriteLine("DirectSoundOut request {0} bytes", count);

            int read =  this.SourceStream.Read(buffer, offset, count);

            // 以下信号処理
            for (int i = 0; i < read/4; i++)
            {

                // float = single = 32bit
                float sample = BitConverter.ToSingle(buffer, i * 4); // Single=4Byte


                // エフェクト処理
                if (Effects.Count == WaveFormat.Channels)
                {
                    sample = Effects[channel].ApplyEffect(sample); // ?
                    channel = (channel + 1) % WaveFormat.Channels; // [1ch, 2ch, ...]
                }

                // float -> byte列に変換
                byte[] bytes = BitConverter.GetBytes(sample); // 4Byteなので,bytes[4]

                // コピー
                //bytes.CopyTo(buffer, i * 4); // 遅い
                buffer[i * 4 + 0] = bytes[0];
                buffer[i * 4 + 1] = bytes[1];
                buffer[i * 4 + 2] = bytes[2];
                buffer[i * 4 + 3] = bytes[3];
            }

            return read;
        }
    }
}

form1.cs

あとは再生系にエフェクトを指定すると使えます。

            // WAV File Open
            OpenFileDialog open = new OpenFileDialog();
            open.Filter = "WAV File (*.wav)|*.wav;";
            if (open.ShowDialog() != DialogResult.OK) return;

            // Audio Chain
            WaveChannel32 wave = new WaveChannel32(new WaveFileReader(open.FileName));
            EffectStream effect = new EffectStream(wave); // エフェクトをかけるためのパイプライン
            stream = new BlockAlignReductionStream(effect);

            // Effects
            for (int i = 0; i < wave.WaveFormat.Channels; i++)
            {
                effect.Effects.Add(new Echo(20000, 0.5f));
            }


            // Out
            output = new DirectSoundOut(200);
            output.Init(stream);
            output.Play();