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Q187673: SAMPLE: AUDIOLVL.EXE-Monitor Input and Output Audio Levels

Article: Q187673
Product(s): Microsoft Visual Basic for Windows
Version(s): WINDOWS:5.0,6.0
Operating System(s): 
Keyword(s): kbfile kbsample kbsound kbAPI kbSDKWin32 kbVBp kbVBp500 kbVBp600 kbWaveAudio kbGrpDSVB
Last Modified: 11-JAN-2001

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The information in this article applies to:

- Microsoft Visual Basic Learning Edition for Windows, versions 5.0, 6.0 
- Microsoft Visual Basic Professional Edition for Windows, versions 5.0, 6.0 
- Microsoft Visual Basic Enterprise Edition for Windows, versions 5.0, 6.0 
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SUMMARY
=======

Audiolbl.exe is a self-extracting compressed file with a Visual Basic project
that displays the input and output volume levels from a sound card. The project
uses several Windows API functions.

MORE INFORMATION
================

The following files are available for download from the Microsoft Download
Center:

  Audiolvl.exe
  (http://download.microsoft.com/download/vb60pro/sample1/1/WIN98/EN-US/Audiolvl.exe)

For additional information about how to download Microsoft Support files, click
the article number below to view the article in the Microsoft Knowledge Base:

  Q119591 How to Obtain Microsoft Support Files from Online Services

Microsoft used the most current virus detection software available on the date of
posting to scan this file for viruses. Once posted, the file is housed on secure
servers that prevent any unauthorized changes to the file.

When you run the self-extracting compressed file, the following files are
expanded into the Audio Level Sample Project directory of your system:

- Form1.frm (6K)- the main form of the project.

- Module1.bas (53K)- the module file with the function declarations.

- Project1.vbp (1K)- the project file.

- Project1.vbw (1K)- the project workspace file.

- Readme.txt - contains the same information as this article.

To run the project, you will need a system with a sound card and a microphone.
Open the project in Visual Basic and click Start from the Run menu. Click the
Get Input button and speak into the microphone. The audio level from the
microphone is displayed in a input level progress bar. Play a .WAV file and the
audio level is displayed in the output level progress bar.

How the Sample Works
--------------------

The sample demonstrates how to display the audio level of an input or output
device. The level is stored in a member of a user-defined type variable. The
sample uses API functions to manipulate several user-defined type variables in
order to extract the audio level.

When you first run the project, the mixerOpen function is used to get a handle to
the mixer device. The handle is used with the mixerGetLineInfo function to get
the capabilities of the mixer device. The capabilities are stored in the
MIXERLINE and the MIXERLINECONTROLS user-defined variables. Some of the members
of these variables are pointers that you need to manipulate in order to control
the mixer. To manipulate these pointers, you need to copy the variables into a
buffer using the GlobalAlloc function. After manipulating the variable members,
you copy the contents of the buffer back to the variable using the RtlMemory
function.

The Timer control is used to query these user-defined variables to get the audio
level. This level is displayed in the appropriate progress bar.

When you click the Get Input button, a user-defined function opens the wave input
device using the waveInOpen function. The waveInOpen function requires the
WAVEFORMAT user-defined type to configure the recording settings such as the
number of channels, the number of sampling bits, and the sampling rate. The wave
input device requires a buffer to process the input data. You create this buffer
with the waveInPrepareHeader function. The buffer is then sent to the wave input
device with the waveInAddBuffer function.

With the buffer created, you can start input on the wave device using the
waveInStart function.

The output level is displayed in a similar fashion.

REFERENCES
==========

For more information about the functions used in this sample project, please see
the following topics in the Platform SDK product documentation:

- Memory Management functions
  GlobalAlloc
  GlobalLock
  GlobalFree
  RtlMoveMemory

- Mixer device functions
  mixerClose
  mixerGetControlDetails
  mixerGetDevCaps
  mixerGetID
  mixerGetLineControls
  mixerGetLineInfo
  mixerGetNumDevs
  mixerMessage
  mixerOpen
  mixerSetControlDetails

- Wave Input device functions
  waveInOpen
  waveInPrepareHeader
  waveInReset
  waveInStart
  waveInStop
  waveInUnprepareHeader
  waveInClose
  waveInGetDevCaps
  waveInGetNumDevs
  waveInGetErrorText
  waveInAddBuffer

For more information about the user-defined types used in this sample, please see
the following topics in the Platform SDL product documentation:

- Mixer device user-defined types
  MIXERCAPS
  MIXERCONTROL
  MIXERCONTROLDETAILS
  MIXERCONTROLDETAILS_SIGNED
  MIXERLINE
  MIXERLINECONTROLS

- Wave device user-defined types
  WAVEHDR
  WAVEINCAPS
  WAVEFORMAT

Additional query words: Audiolvl>

======================================================================
Keywords          : kbfile kbsample kbsound kbAPI kbSDKWin32 kbVBp kbVBp500 kbVBp600 kbWaveAudio kbGrpDSVB kbDSupport 
Technology        : kbVBSearch kbAudDeveloper kbZNotKeyword6 kbZNotKeyword2 kbVB500Search kbVB600Search kbVBA500 kbVBA600 kbVB500 kbVB600
Version           : WINDOWS:5.0,6.0
Issue type        : kbhowto

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