A Sound Output class

Friday Feb 5th 1999 by Yannick Sustrac
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A Sound Output class

Description:

In the previous article http://www.codeguru.com/multimedia/scope_input_sound_class.shtml we talked about the SoundIn class which was provided to interface a sound card for input signal. The idea is now to create a class for an Output sound .

The Sound Output class which is provided now, to be used as a generator, is very similar to the Input class one. In fact, it has been realised in a very short time by replacing all the "In" string in the CSoundIn class by the "Out" and by replacing the correct names in the base functions of the Win32 Sound Api .

The CSoundOut::OpenOutput() is now the main start procedure. It initialise all the parametres of the sound card, create an EVENT object and start the sound thread. The thread procedure is now used to signal to the sound class, (instead that a buffer is filled for the Input) ,that it has been transmited to the Sound card and the Win Sound system is now requiring some new datas for transmiting.

How to use it

  • In the same way that the way we use for the Input Sound you just have to include the 2 Sound Output class files in ur project
  • The sample demo program use ....the same "quick & dirty" global declaration CSoundOut SoundOut; in CSndApp.cpp.
  • Call the function OpenOutput(); in the InitInstance App procedure. (the CloseOutput() at ExitIntance is optional)

This is all you need to start the Sound process for audio Output.

The Scope View:

Is unchanged. it will display the Input which is a mix of the Input (Equvalent to the Mic) and the Output (Equivalent to the Wave).

Run the scope/generator demo program:

In the new Demo sample the SoundIn class is still active, a menu has been added to start/Stop the both Sound process. Because some Sound system does'nt provide full duplex Input/Output you may be required to start & stop selectively the 2 process. If you modify the sampling rate, you must also take into account that the Sound card use the same frequency rate for both Input/Ouput and that the classes parametres must be set at the same one.

Before running it, let's have a look at the "reame.txt" file included in the project demo.

Update

Thanks to peoples who have contributed to this update

As Tom Wheeler mentioned ,the CSoundOut use now 2 buffers which are feed to the sound system, I saw source code sound applications (like playing wave file)that use more than 2 buffers which are feed to the sound system. When the fisrt buffer has been played the thread is notified to send an other one to the sound system. In this way the sound system has alway a buffer to play and this avoid time leak beetwin buffers.

An other problem is that the generator samples must be continus for the 2 buffers, if the sampling frequency change and the sound signal frequency also change, it is not really simple to have the boths buffers exactly synchronized to a precise number of periodes. The CSinGenerator class derived from CSoundOut has been added which resolve this kind of problem by using a special Sinusoid Oscillator algorithm. This is not a place to develop this signal processing application ,but readers can D/L the "goertzel.zip" file from my web to get.more informations.

Download the new demo code - 40 Kb

Ps: If you are a little bit lazy to enhance the program by yourself..., you can get my full application for signal processing here: http://www.multimania.com/yannstrc go to Visual Sound Processing Studio page and enjoy it!

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