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Simple Audio Out Oscilloscope and Spectrum Analyzer

, 27 Jul 2006 CPOL
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An example of how to access the Audio Mix, sample audio output, and a simple DSP processing.

Sample Image


This is a simple application I built to understand the basics of the Windows Audio WAVE API, and to get a basic grasp on Fast Fourier Transforms (FFTs). Features of the application are: double buffering graphics, sampling an audio source, selecting an audio recording source using the mixer, calculating the FFT spectrum array, and plotting sampled data.


I won't discus the details of FFT here as the math is a little beyond me. Basically, it involves complex numbers (those number like sqrt(-1)) and calculating discrete Sin/Cos transformations on sampled date. Google for many and better explanations on FFT.

Using the code

If you look through the example, you will find it quite a simple affair that has not been touched by MFC. This means that the code is easy to follow and easy to transplant into your projects. The basic flow of the program is:

  • Load a dialog window and initialize it.
  • Select the recording device (which is harder than it should be!).
  • Initialize the WAVE structures.
  • Activate the sampling.
  • Determine the status of the sampling.
  • Process the sampled data using FFT.
  • Clean up.

In the FFT process, I load the sampled data into an iterator class for processing within the FFT class. This allow for selective processing of the sampled data. In this case, I sampled the recording source in stereo, and I can selectively process the left or the right channels within the FFT class, or both channels at once. Both classes are simple to follow and to implement.

Points of interest

The audio device API within Windows is far more complex than it should be. This is pretty common when dealing with Microsoft, they never seem to make things easy! A classic example is dealing with the Audio Mixer. It took some time to find some code that can do the most basic of tasks (select a recording device), and even that is not 100% perfect. Device drivers may incorrectly label a recording device as a WAVEOUT device and the program will return an error when trying to record from it, so look out for such errors (use the VC6 debugger to determine the fault in such occurrences).

In fact, I would not recommend using the WAVE API for anything too complex as it tends to be a bit tricky to use, instead look at the Simple Directmedia Layer library, and specifically the mixer lib, which is a good example of making things simple and useful to the programmer.

The FFT implementation probably isn't the fastest around. I originally converted the source from a Java class, and then optimized the Cos/Sin processing to implement a look up table to speed things up significantly, and added a few helper methods; otherwise it has remained unchanged.


  • Updated the spectrum graphics to be more equalised.
  • Fixed a number of small bugs.


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

Steven De Toni
New Zealand New Zealand
No Biography provided

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Comments and Discussions

QuestionRe: SetInputDevice: hMixer Undefined Value. Please help. [modified] Pin
jeffhcliu14-Jun-07 19:29
memberjeffhcliu14-Jun-07 19:29 
QuestionCould not download source file Pin
david_taipei7-Jun-07 22:56
memberdavid_taipei7-Jun-07 22:56 
QuestionHelp in Converting "Callback Scope". Thanks. Pin
jeffhcliu7-Jun-07 9:40
memberjeffhcliu7-Jun-07 9:40 
AnswerRe: Help in Converting "Callback Scope". Thanks. Pin
Steven De Toni7-Jun-07 14:37
memberSteven De Toni7-Jun-07 14:37 
GeneralRe: Help in Converting "Callback Scope". Thanks. Pin
jeffhcliu7-Jun-07 15:25
memberjeffhcliu7-Jun-07 15:25 
Generalsound card with 3 mixers Pin
kenadams11129-Mar-07 4:15
memberkenadams11129-Mar-07 4:15 
GeneralMore Advanced Version of Audio Scope Pin
Steven De Toni26-Mar-07 19:21
memberSteven De Toni26-Mar-07 19:21 
QuestionAny flowchart or psuedo code available for this project Pin
Vidyadhar_India26-Mar-07 17:58
memberVidyadhar_India26-Mar-07 17:58 
AnswerRe: Any flowchart or psuedo code available for this project Pin
Steven De Toni26-Mar-07 19:18
memberSteven De Toni26-Mar-07 19:18 
Questionhow to get amplitude and frequency Pin
lowkt2-Mar-07 4:34
memberlowkt2-Mar-07 4:34 
QuestionStrange behaviour and Equalizer Pin
GianniGP29-Jan-07 1:09
memberGianniGP29-Jan-07 1:09 
AnswerRe: Strange behaviour and Equalizer Pin
GianniGP31-Jan-07 4:45
memberGianniGP31-Jan-07 4:45 
QuestionRe: Strange behaviour and Equalizer Pin
jeffhcliu9-Jun-07 11:17
memberjeffhcliu9-Jun-07 11:17 
GeneralWant to convert this in C# Pin
Indian Ocean7-Jan-07 4:13
memberIndian Ocean7-Jan-07 4:13 
GeneralRe: Want to convert this in C# Pin
Steven De Toni10-Jan-07 17:01
memberSteven De Toni10-Jan-07 17:01 
GeneralRe: Want to convert this in C# Pin
Tauhid Shaikh23-Sep-07 20:58
memberTauhid Shaikh23-Sep-07 20:58 
GeneralRe: Want to convert this in C# Pin
osirisgothra7-Nov-07 3:37
memberosirisgothra7-Nov-07 3:37 
GeneralSmall bug for spectrum calculation Pin
mcanti2-Dec-06 2:19
membermcanti2-Dec-06 2:19 
QuestionCompile ERROR in VC 2003? [modified] Pin
descartes6-Nov-06 0:33
memberdescartes6-Nov-06 0:33 
AnswerRe: Compile ERROR in VC 2003? Pin
Estrayk11-Feb-07 8:13
memberEstrayk11-Feb-07 8:13 
GeneralRe: Compile ERROR in VC 2003? Pin
CarEnMDC11-Apr-07 19:03
memberCarEnMDC11-Apr-07 19:03 
QuestionJust a bit of help needed Pin
morfyh10-Oct-06 7:05
membermorfyh10-Oct-06 7:05 
AnswerRe: Just a bit of help needed Pin
Steven De Toni10-Oct-06 11:04
memberSteven De Toni10-Oct-06 11:04 
GeneralRe: Just a bit of help needed Pin
morfyh10-Oct-06 22:23
membermorfyh10-Oct-06 22:23 
QuestionModifications/improvement Pin
Irlande7818-Sep-06 4:17
memberIrlande7818-Sep-06 4:17 
NewsRe: Modifications/improvement Pin
Manni Singh13-Oct-06 18:16
memberManni Singh13-Oct-06 18:16 
QuestionRe: Modifications/improvement Pin
Irlande7814-Oct-06 0:27
memberIrlande7814-Oct-06 0:27 
AnswerRe: Modifications/improvement Pin
Steven De Toni14-Oct-06 0:57
memberSteven De Toni14-Oct-06 0:57 
GeneralRe: Modifications/improvement Pin
Steven De Toni14-Oct-06 0:41
memberSteven De Toni14-Oct-06 0:41 
QuestionRe: Modifications/improvement Pin
Irlande7814-Oct-06 1:09
memberIrlande7814-Oct-06 1:09 
QuestionHow to select another mixer ? Pin
Manni Singh1-Sep-06 9:43
memberManni Singh1-Sep-06 9:43 
AnswerRe: How to select another mixer ? Pin
Steven De Toni3-Sep-06 0:19
memberSteven De Toni3-Sep-06 0:19 
QuestionHow to get Average Value not the Peak ? Pin
Manni Singh11-Aug-06 0:25
memberManni Singh11-Aug-06 0:25 
AnswerRe: How to get Average Value not the Peak ? Pin
Steven De Toni10-Oct-06 13:02
memberSteven De Toni10-Oct-06 13:02 
QuestionHow can I get sound from speaker and mic? Pin
Guto Garcia28-Jul-06 3:52
memberGuto Garcia28-Jul-06 3:52 
AnswerRe: How can I get sound from speaker and mic? Pin
Steven De Toni29-Jul-06 0:09
memberSteven De Toni29-Jul-06 0:09 
GeneralGreat! Pin
Jörg Anslik27-Jul-06 12:38
memberJörg Anslik27-Jul-06 12:38 
GeneralBug Fix For SampleIter Class [modified] Pin
Steven De Toni26-Jul-06 11:28
memberSteven De Toni26-Jul-06 11:28 
GeneralThanks for the contrib... Pin
doug435026-Jul-06 10:26
memberdoug435026-Jul-06 10:26 
QuestionNeed Help ?? Pin
Manni Singh25-Jul-06 10:03
memberManni Singh25-Jul-06 10:03 
AnswerRe: Need Help ?? [modified] Pin
Steven De Toni26-Jul-06 14:12
memberSteven De Toni26-Jul-06 14:12 
GeneralRe: Need Help ?? Pin
Manni Singh27-Jul-06 8:28
memberManni Singh27-Jul-06 8:28 
GeneralVery nice, very useful :) Pin
Kochise22-Jul-06 12:15
memberKochise22-Jul-06 12:15 
GeneralSin/Cos Speedup [modified] Pin
Steven De Toni20-Jul-06 11:52
memberSteven De Toni20-Jul-06 11:52 
Generalim soo thnnfullllllllllllllll.... Pin
Manni Singh20-Jul-06 6:27
memberManni Singh20-Jul-06 6:27 
GeneralRe: im soo thnnfullllllllllllllll.... Pin
Colin Angus Mackay20-Jul-06 6:46
memberColin Angus Mackay20-Jul-06 6:46 

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