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Sound Activated Recorder with Spectrogram in C#

, 27 Jan 2008 GPL3
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Audio event processing with visual display
SoundCatcher

Introduction

This project demonstrates an implementation of the waterfall spectrogram and use of statistical data to trigger events in near real-time. This code is an elaboration of my previous submission (SoundViewer). This demonstration utilizes the Wave classes developed by Ianier Munoz.

Using the Code

Audio is supplied by the default input device which is typically the microphone. Events are triggered when audio amplitude exceeds the desired threshold value, which can be set under Options on the menu bar. To make this more useful, I've added functionality to save the stream to disk which results in a nice sound activated recorder.

Points of Interest

In order to draw the spectrogram fast enough to allow for near real-time operation, I needed to write directly to memory using unsafe code.

// lock image
PixelFormat format = canvas.PixelFormat;
BitmapData data = 
    canvas.LockBits(new Rectangle(0, 0, width, height), ImageLockMode.ReadOnly, format);
int stride = data.Stride;
int offset = stride - width * 4;

// draw image
try
{
  unsafe
  {
    byte* pixel = (byte*)data.Scan0.ToPointer();
    // for each column
    for (int y = 0; y <= height; y++)
    {
      if (y < _fftLeftSpect.Count)
      {
        // for each row
        for (int x = 0; x < width; x++, pixel += 4)
        {
          double amplitude = ((double[])_fftLeftSpect[_fftLeftSpect.Count - y - 1])
                [(int)(((double)(_fftLeft.Length) / (double)(width)) * x)];
          double color = GetColor(min, max, range, amplitude);
          pixel[0] = (byte)0;
          pixel[1] = (byte)color;
          pixel[2] = (byte)0;
          pixel[3] = (byte)255;
        }
        pixel += offset;
      }
    }
  }
}
catch (Exception ex)
{
  Console.WriteLine(ex.ToString());
}

// unlock image
canvas.UnlockBits(data);

I noticed that the results vary wildly depending on the hardware and associated drivers being used.

Some things I'd like to experiment with further when I get the time:

  1. Use of frequency domain to produce "motion" detector equivalent
  2. Use of spectrogram in sound identification
  3. Improving performance/robustness

History

  • 01/16/2008: Created

License

This article, along with any associated source code and files, is licensed under The GNU General Public License (GPLv3)

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About the Author

Jeff Morton
Systems / Hardware Administrator
United States United States
No Biography provided

Comments and Discussions

 
GeneralRe: Bug in event detection - left channel only is used PinmemberJeff Morton9-Oct-08 13:16 
GeneralAnother hi! Pinmemberstano24-Sep-08 19:16 
GeneralAnger detection software Pinmember100,000 Cold Calls12-Aug-08 12:44 
GeneralRe: Anger detection software Pinmemberflowerchild128-Feb-09 13:48 
Generalthe file is not saving ...!! PinmemberAshok Nalam9-Jul-08 2:05 
QuestionDisplay Of Frequencies PinmemberRonD25-May-08 5:17 
AnswerRe: Display Of Frequencies PinmemberMember 47088011-Aug-08 16:24 
GeneralRe: Display Of Frequencies PinmemberMember 47088011-Aug-08 16:25 
actually it should read N/2-1 but it makes little difference
QuestionHow can i make it faster? Pinmemberpauloricca16-May-08 7:20 
AnswerRe: How can i make it faster? PinmemberJeff Morton16-May-08 8:05 
GeneralRe: How can i make it faster? Pinmemberpauloricca19-May-08 0:42 
GeneralTwo Questions Pinmemberrodriguesd23-Mar-08 1:45 
GeneralThis is great stuff Pinmemberpeter.roca6-Mar-08 10:34 
GeneralHi Pinmembercircass4-Mar-08 7:32 
GeneralJust a thought... PinmemberEd.Poore29-Jan-08 14:53 
QuestionProblem with Solution file? PinmemberEitsopGmail29-Jan-08 0:41 
AnswerRe: Problem with Solution file? PinmemberJeff Morton29-Jan-08 1:16 
GeneralRe: Problem with Solution file? Pinmembercircass4-Mar-08 7:34 

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