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Sound Activated Recorder with Spectrogram in C#

By , 27 Jan 2008
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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)

About the Author

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

Comments and Discussions

 
QuestionHow to generate wave-form if we have the byte-array with us. PinmemberMark0211-Mar-10 23:06 
GeneralIntegration Time PinmemberGeoNav17-Feb-10 4:17 
GeneralSound Equalizer PinmemberBazKhan25-Jan-10 19:34 
GeneralAmplitude -sound loudness Pinmemberginwithlime9-Jan-10 4:10 
GeneralRe: Amplitude -sound loudness PinmemberJeff Morton9-Jan-10 5:36 
QuestionHow to stop the thread if a invoke methode gets called in the DataArrived Event PinmemberMichael Muehllehner7-Dec-09 3:57 
QuestionHow to make the IFFT? Pinmemberafmf3-Nov-09 5:33 
I made an high pass filter after the FFT and I wanted to record the result.
For that, I need to do a IFFT.
Can you tell me how do I do it with your code? tks
 
aF -.-

AnswerRe: How to make the IFFT? PinmemberRahdu23-Sep-10 9:35 
QuestionHow to reduce the noise? PinmemberGeoNav31-Oct-09 1:55 
Generallineout audio PinmemberGeoNav28-Oct-09 23:10 
QuestionChange Source to wav file PinmemberGeoNav21-Oct-09 21:36 
AnswerRe: Change Source to wav file PinmemberJeff Morton22-Oct-09 11:23 
GeneralRe: Change Source to wav file PinmemberGeoNav26-Oct-09 18:35 
GeneralRe: Change Source to wav file Pinmemberafmf3-Nov-09 5:38 
AnswerRe: Change Source to wav file Pinmemberravitzur18-Dec-10 23:07 
GeneralError in Program PinmemberPiligrim200720-Oct-09 11:04 
GeneralRe: Error in Program PinmemberJeff Morton22-Oct-09 11:23 
GeneralRe: Error in Program PinmemberPiligrim200724-Oct-09 0:52 
QuestionCan't run the program in Vista 64bit PinmemberYasir Salih Osman7-Aug-09 22:36 
AnswerRe: Can't run the program in Vista 64bit PinmemberFullmetal9901211-Sep-09 7:20 
AnswerRe: Can't run the program in Vista 64bit PinmemberRahdu18-Oct-10 22:09 
AnswerRe: Can't run the program in Vista 64bit PinmemberMember 320938312-Apr-11 12:10 
AnswerRe: Can't run the program in Vista 64bit PinmemberRebmem1529-Sep-11 18:33 
Questionhow can i do it reverse? [modified] Pinmembermojimoj2-Aug-09 21:05 
GeneralExcellent piece of work Jeff Pinmembermaxima1204-Jul-09 12:17 

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