VolumeMeter (Managed DirectX)

• Download source files - 147 Kb
• Download demo project - 139 Kb

Introduction

This project is a live volume meter control for monitoring audio levels from a sound card. It is written entirely in C#, and uses Microsoft's Managed DirectX (June release). You can drag-and-drop the control into any Windows Forms application. You may select the input, and tweak the appearance of the animation through various parameters.

The idea behind this project is to maintain a very short buffer of audio and constantly record into it. The control is on a timer, and periodically queries the buffer to see what volume level the most recent sample has, and then sets a progress bar's value accordingly.

There are commercial controls that achieve the same purpose, but I wanted to dive in and get my hands dirty with DirectX (albeit the managed version :) ). I hope others will benefit from this work.

Using the code

This project consists of four DLLs: volumemeter.dll, progressbargradient.dll, Microsoft.DirectX.dll, and Microsoft.DirectX.DirectSound.dll. To use this control in a project, right-click in the toolbox, select "Choose Controls", and browse for volumemeter.dll. You don't need to manually reference any of the other DLLs, but they do need to be present. The control should now be present in your toolbox, so drag it onto a form to add it to your project. The control is active even while in the Visual Studio designer, so you can see it in action without having to run the project.

The following methods are available to you:

• Start() - starts the animation, provided an audio device has been set through SelectedDeviceIndex or SelectedDeviceName.
• Stop() - halts the animation.

The following properties are available to you:

• AutoStart - if true, whenever you change the audio source (through SelectedDeviceIndex or SelectedDeviceName) and the meter animation is currently turned off, the control will start the animation.
• BorderStyle - sets the appearance of the border around each progress bar.
• DeviceNames - a list of the audio devices present in the system.
• Orientation - sets the volume bars to run horizontally or vertically.
• SelectedDeviceIndex - gets or sets the index of the current audio device according to the list in DeviceNames. If you enter an index out of bounds of the DeviceNames list, the meter stops running.
• SelectedDeviceName - gets or sets the name of the current audio device according to the list in DeviceNames If you enter a name which is not contained in the DeviceNames list, the meter stops running. Note that while you can select a device through the control, you must adjust the recording properties of that device through Windows Volume Control or some other program.
• VisualizerOn - set to true to start the animation, false to stop. You can achieve the same results with the Start() and Stop(), but this property is useful for toggling without having to check the current state first.

  Altering the following properties is not necessary for operating the control, but this information is here just for reference. The defaults are fine for most projects.

• SampleDelay - how often the control queries the capture buffer to get the volume, measured in milliseconds. Values between 80 and 140 generally give good results, default is 100.
• FrameDelay - the time in milliseconds between animation frames, measured in milliseconds. Values between 10 and 40 generally give good results, default is 10. This value must be less than or equal to SampleDelay.

  The last two values work together to provide a smooth animation. SampleDelay dictates how often a real value is read from the sound card, but in-between those capture points, the control interpolates frames to keep the animation running smoothly. This gives much better results than just polling the audio card and updating the progress bar's value (which, by the way, you can simulate by setting FrameDelay = SampleDelay).

The following events are available to you:

• VolumeChanged fires whenever a new sample is read that differs from the previous one. The event uses a VolumeChangedEventArgs class to send information about the old and new volume levels.

Points of Interest

This control uses GDI+ to run all the animation, so if you size the control to full-screen, you will most likely see a very high CPU usage. You can lower that usage by increasing the SampleDelay and/or FrameDelay values. Notice, however, that the animation runs in a separate thread that is set to have a very low priority, so this control will not cause your project to hang.

The progress bars in this project are custom controls I built. They let you use a gradient fill rather than a plain old solid color. If you want to use them independent of this project, just add the "ProgressBarGradient.dll" to your toolbox. I might post the ProgressBarGradient project online if/when I get around to it.

If you're interested in how to use managed DirectX, here's the code for starting the audio capture buffer:

// initialize the capture buffer and start the animation thread

Capture cap = new Capture(audioDevices[deviceIndex].DriverGuid);
CaptureBufferDescription desc = new CaptureBufferDescription();

WaveFormat wf = new WaveFormat();
wf.BitsPerSample = 16;
wf.SamplesPerSecond = 44100;
wf.Channels = 2;
wf.BlockAlign = (short)(wf.Channels * wf.BitsPerSample / 8);
wf.AverageBytesPerSecond = wf.BlockAlign * wf.SamplesPerSecond;
wf.FormatTag = WaveFormatTag.Pcm;


desc.Format = wf;
desc.BufferBytes = SAMPLES * wf.BlockAlign;
    
buffer = new Microsoft.DirectX.DirectSound.CaptureBuffer(desc, cap);
buffer.Start(true);

liveVolumeThread = new Thread(new ThreadStart(updateProgress));    
liveVolumeThread.Priority = ThreadPriority.Lowest;
liveVolumeThread.Start();

And here's how you read values from the buffer:

private const int SAMPLES = 8;
private static int[] SAMPLE_FORMAT_ARRAY = {SAMPLES, 2, 1};
...

Array samples = buffer.Read(0, typeof(Int16), LockFlag.FromWriteCursor, 
                            SAMPLE_FORMAT_ARRAY);

Etc.

I have tested and used this control on only a few different machines, so no guarantees about how well it will run for you. The usual disclaimers apply - run this code at your own risk, I am not responsible if you lose your firstborn because of some bug in the code :). That said, I have not encountered any problems using this control in my own projects. Feel free to contact me with any bugs or suggestions. Enjoy!

History

• v1.0 - Released 7/27/2006.