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Sound Activated Recorder with Spectrogram in C#

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27 Jan 2008GPL3 399.6K   32.1K   207   105
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.

C#
// 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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Comments and Discussions

 
QuestionHow do I get it to work? Pin
Maiden Computer Company22-Apr-09 10:48
Maiden Computer Company22-Apr-09 10:48 
AnswerRe: How do I get it to work? Pin
Jeff Morton22-Apr-09 10:51
Jeff Morton22-Apr-09 10:51 
QuestionError in Frequency domain? Pin
Elysium8-Mar-09 11:17
Elysium8-Mar-09 11:17 
AnswerRe: Error in Frequency domain? Pin
Jeff Morton8-Mar-09 11:41
Jeff Morton8-Mar-09 11:41 
GeneralRe: Error in Frequency domain? Pin
Elysium8-Mar-09 22:02
Elysium8-Mar-09 22:02 
I did have another thought I'll need to check...to get the single spike in the freq domain you'll need an integral number of sine wave cycles in your sample window otherwise you will see some other spurious frequency content (not sure if that is what we are seeing).
QuestionQuestion on how to get the frequencies Pin
kyanmark_johnwill2-Mar-09 13:52
kyanmark_johnwill2-Mar-09 13:52 
AnswerRe: Question on how to get the frequencies Pin
hazeljane13-Mar-09 3:49
hazeljane13-Mar-09 3:49 
GeneralRe: Question on how to get the frequencies Pin
Jeff Morton13-Mar-09 10:34
Jeff Morton13-Mar-09 10:34 
GeneralRe: Question on how to get the frequencies Pin
afmf23-Oct-09 1:54
afmf23-Oct-09 1:54 
GeneralRe: Question on how to get the frequencies Pin
afmf2-Nov-09 23:38
afmf2-Nov-09 23:38 
GeneralRe: Question on how to get the frequencies Pin
Muammar©1-Jan-10 0:56
Muammar©1-Jan-10 0:56 
Questionspectrogram of a wav file Pin
plouvou12-Jan-09 9:59
plouvou12-Jan-09 9:59 
AnswerRe: spectrogram of a wav file Pin
Tae-Sung18-Jan-09 9:07
Tae-Sung18-Jan-09 9:07 
GeneralRe: spectrogram of a wav file Pin
tortexy2-Feb-09 12:50
tortexy2-Feb-09 12:50 
GeneralRe: spectrogram of a wav file Pin
GeoNav31-Oct-09 1:52
GeoNav31-Oct-09 1:52 
GeneralDraw waveform for already existing wave file Pin
jugal_piet@indiatimes.com5-Jan-09 20:26
jugal_piet@indiatimes.com5-Jan-09 20:26 
GeneralVery great app Pin
Mr. Yi26-Nov-08 4:31
Mr. Yi26-Nov-08 4:31 
GeneralBug in event detection - left channel only is used Pin
Atis Straujums9-Oct-08 10:43
Atis Straujums9-Oct-08 10:43 
GeneralRe: Bug in event detection - left channel only is used Pin
Jeff Morton9-Oct-08 12:16
Jeff Morton9-Oct-08 12:16 
GeneralAnother hi! Pin
stano24-Sep-08 18:16
stano24-Sep-08 18:16 
GeneralRe: Anger detection software Pin
flowerchild128-Feb-09 12:48
flowerchild128-Feb-09 12:48 
Generalthe file is not saving ...!! Pin
Ashok Nalam9-Jul-08 1:05
Ashok Nalam9-Jul-08 1:05 
QuestionDisplay Of Frequencies Pin
RonD25-May-08 4:17
RonD25-May-08 4:17 
AnswerRe: Display Of Frequencies Pin
Member 47088011-Aug-08 15:24
Member 47088011-Aug-08 15:24 
GeneralRe: Display Of Frequencies Pin
Member 47088011-Aug-08 15:25
Member 47088011-Aug-08 15:25 

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