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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


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
    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)

// unlock image

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


  • 01/16/2008: Created


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

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Comments and Discussions

Questionis there a way to select the iinput device (directx name ?) Pin
patrick zuili17-Mar-13 19:34
memberpatrick zuili17-Mar-13 19:34 
Generalamazing one Pin
Member 810718412-Jan-13 6:07
memberMember 810718412-Jan-13 6:07 
GeneralMy vote of 5 Pin
javcastaalm23-Nov-12 10:08
memberjavcastaalm23-Nov-12 10:08 
GeneralThanks Pin
LeviButler3-Nov-12 14:27
memberLeviButler3-Nov-12 14:27 
GeneralMy vote of 5 Pin
Member 806726522-May-12 1:47
memberMember 806726522-May-12 1:47 
Questiondraw spectrogram with a wav file. Pin
jacky_zz4-Feb-12 19:27
memberjacky_zz4-Feb-12 19:27 
QuestionLocking up when closing if there is activity Pin
programmerdon17-Jan-12 6:46
memberprogrammerdon17-Jan-12 6:46 
QuestionObject reference not set to an instance of an object Pin
deepak thomas5-Dec-11 5:01
memberdeepak thomas5-Dec-11 5:01 
AnswerRe: Object reference not set to an instance of an object Pin
deepak thomas5-Dec-11 7:57
memberdeepak thomas5-Dec-11 7:57 
GeneralRe: Object reference not set to an instance of an object Pin
Member 1029319526-Sep-13 19:08
memberMember 1029319526-Sep-13 19:08 
QuestionSound Catcher freezes on Exit in Win 7 32-bit Pin
Member 836994911-Nov-11 12:13
memberMember 836994911-Nov-11 12:13 
AnswerRe: Sound Catcher freezes on Exit in Win 7 32-bit Pin
Timothy Ayodele14-Jan-12 2:54
memberTimothy Ayodele14-Jan-12 2:54 
QuestionPlease how can i make the recording every 1 hour Pin
Timothy Ayodele2-Nov-11 8:26
memberTimothy Ayodele2-Nov-11 8:26 
QuestionVote 5 Pin
serega4675-Aug-11 1:41
memberserega4675-Aug-11 1:41 
GeneralIn VB.NET Pin
emicroxxx23-May-11 3:55
memberemicroxxx23-May-11 3:55 
GeneralMy vote of 5 Pin
abdillahi26-Apr-11 23:23
groupabdillahi26-Apr-11 23:23 
QuestionHow can i save output to .txt ? Pin
stefan_brato27-Nov-10 17:48
memberstefan_brato27-Nov-10 17:48 
QuestionSpectrogram Disappears Pin
GeoNav12-Jul-10 19:26
memberGeoNav12-Jul-10 19:26 
QuestionGPLv2 Pin
Member 42771197-Jul-10 11:00
memberMember 42771197-Jul-10 11:00 
QuestionHow to generate wave-form if we have the byte-array with us. Pin
Mark0212-Mar-10 0:06
memberMark0212-Mar-10 0:06 
GeneralIntegration Time Pin
GeoNav17-Feb-10 5:17
memberGeoNav17-Feb-10 5:17 
GeneralSound Equalizer Pin
BazKhan25-Jan-10 20:34
memberBazKhan25-Jan-10 20:34 
GeneralAmplitude -sound loudness Pin
ginwithlime9-Jan-10 5:10
memberginwithlime9-Jan-10 5:10 
GeneralRe: Amplitude -sound loudness Pin
Jeff Morton9-Jan-10 6:36
memberJeff Morton9-Jan-10 6:36 
QuestionHow to stop the thread if a invoke methode gets called in the DataArrived Event Pin
Michael Muehllehner7-Dec-09 4:57
memberMichael Muehllehner7-Dec-09 4:57 
i want to use this great application to show me the loudest frequency in the fft. It works very well, the RenderFrequencyDomain allready calculates the loudest frequency.
I have to use a invoke to display this number on a textbox. The application works, i got the frequency displayed on a textbox, but i can not stop the thread.

Code in the DataArrived Methode: (i returned the maxHz in the RenderFrequencyDomainLeft)

double leftHz = _audioFrame.RenderFrequencyDomainLeft(...)
Invoke(new MethodInvoker(delegate{
   textBox1.Text = leftHz.ToString() + " Hz";

When i want to close the application the call stack hangs in the following step:
- FormOnClosing
-> Stop();
-> _recorder.Dispose();
-> WaitForAllBuffers();
-> Buf.WaitFor();
-> m_Recording = m_RecordEvent.WaitOne(); // The WaitOne Methode hangs

If i give a timeout to the WaitOne Methode, the closing call stack hangs in the following step:
- FormOnClosing
-> Stop();
-> _recorder.Dispose();
-> m_Thread.Join(); // The Join Methode hangs

If i give a timeout to the Join Methode, i got a objectdisposedexeption in the Invoke Methode i wrote for updating the textbox.

I want to know if there is any good solution to access user controls with an invoke in the dataarrived event. And with that i can stop the threads without timeout programming.

thx a lot

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