How to render audio waveform?

Question

1. Is there any audio/programming-related stack-exchange site?
2. I'm trying to make a wave form in WinForms
3. What algorithm should I use?

For example, if I have 200 samples per pixel (vertical line), should I draw the lowest and the highest sample from that portion of 200 samples? Or should I draw average of low and high samples? Maybe both in different colors?

Answer 1

This will help you to generate waveform from audio file using nAudio in C#...

using NAudio.Wave;
using System;
using System.Collections.Generic;
using System.Drawing;
using System.IO;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class test : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
    string strPath = Server.MapPath("audio/060.mp3");
    string SongID = "2";
    byte[] bytes = File.ReadAllBytes(strPath);
    WriteToFile(SongID,strPath, bytes);
    Response.Redirect("Main.aspx");
    }

private void WriteToFile(string SongID, string strPath, byte[] Buffer)
{
    try
    {
        int samplesPerPixel = 128;
        long startPosition = 0;
        //FileStream newFile = new FileStream(GeneralUtils.Get_SongFilePath() + "/" + strPath, FileMode.Create);
        float[] data = FloatArrayFromByteArray(Buffer);

        Bitmap bmp = new Bitmap(1170, 200);

        int BORDER_WIDTH = 5;
        int width = bmp.Width - (2 * BORDER_WIDTH);
        int height = bmp.Height - (2 * BORDER_WIDTH);

        NAudio.Wave.Mp3FileReader reader = new NAudio.Wave.Mp3FileReader(strPath, wf => new NAudio.FileFormats.Mp3.DmoMp3FrameDecompressor(wf));
        NAudio.Wave.WaveChannel32 channelStream = new NAudio.Wave.WaveChannel32(reader);

        int bytesPerSample = (reader.WaveFormat.BitsPerSample / 8) * channelStream.WaveFormat.Channels;

        using (Graphics g = Graphics.FromImage(bmp))
        {

            g.Clear(Color.White);
            Pen pen1 = new Pen(Color.Gray);
            int size = data.Length;

            string hexValue1 = "#009adf";
            Color colour1 = System.Drawing.ColorTranslator.FromHtml(hexValue1);
            pen1.Color = colour1;

            Stream wavestream = new NAudio.Wave.Mp3FileReader(strPath, wf => new NAudio.FileFormats.Mp3.DmoMp3FrameDecompressor(wf));

            wavestream.Position = 0;
            int bytesRead1;
            byte[] waveData1 = new byte[samplesPerPixel * bytesPerSample];
            wavestream.Position = startPosition + (width * bytesPerSample * samplesPerPixel);

            for (float x = 0; x < width; x++)
            {
                short low = 0;
                short high = 0;
                bytesRead1 = wavestream.Read(waveData1, 0, samplesPerPixel * bytesPerSample);
                if (bytesRead1 == 0)
                    break;
                for (int n = 0; n < bytesRead1; n += 2)
                {
                    short sample = BitConverter.ToInt16(waveData1, n);
                    if (sample < low) low = sample;
                    if (sample > high) high = sample;
                }
                float lowPercent = ((((float)low) - short.MinValue) / ushort.MaxValue);
                float highPercent = ((((float)high) - short.MinValue) / ushort.MaxValue);
                float lowValue = height * lowPercent;
                float highValue = height * highPercent;
                g.DrawLine(pen1, x, lowValue, x, highValue);

            }
        }

        string filename = Server.MapPath("image/060.png");
        bmp.Save(filename);
        bmp.Dispose();

    }
catch (Exception e)
    {

    }
}
public float[] FloatArrayFromStream(System.IO.MemoryStream stream)
{
    return FloatArrayFromByteArray(stream.GetBuffer());
}

public float[] FloatArrayFromByteArray(byte[] input)
{
    float[] output = new float[input.Length / 4];
    for (int i = 0; i < output.Length; i++)
    {
        output[i] = BitConverter.ToSingle(input, i * 4);
    }
    return output;
}

}

Answer 2

1. Try dsp.stackexchange.com

2. At 200 samples per pixel, there are several approaches you can try. Whatever you do, it often works best to draw each vertical line both above and below 0, ie. treat positive and negative sample values seperately. Probably the easiest is to just calculate an RMS. At such a low resolution peak values will probably give you a misleading representation of the waveform.