Copyright © 2001-2019 MultiMedia Soft How to access settings of audio devices in Windows Vista and later versions

[This tutorial applies to Windows Vista and later versions only]

 

Starting from Windows Vista, Microsoft has rewritten the multimedia sub-system of the Windows operating system from the ground-up; at the same time Microsoft introduced a new API, also known as Core audio API, which allows interacting with the multimedia sub-system and with audio endpoint devices (sound cards).

 

The Core Audio APIs implemented in Windows Vista and higher versions are the following:

• Multimedia Device (MMDevice) API. Clients use this API to enumerate the audio endpoint devices in the system.

• DeviceTopology API. Clients use this API to directly access the topological features (for example, volume controls and multiplexers) that lie along the data paths inside hardware devices in audio adapters.

• EndpointVolume API. Clients use this API to directly access the volume controls on audio endpoint devices. This API is primarily used by applications that manage exclusive-mode audio streams.

• Windows Audio Session API (WASAPI). Clients use this API to create and manage audio streams to and from audio endpoint devices.

 

Audio DJ Studio for .NET encapsulates a small portion of these APIs inside a set of methods and events which allow communicating with audio endpoint devices and to request information about their status, to obtain/set the volume level, to mute/unmute specific channels, to report values of embedded VU-meters and so on.

 

All of the mentioned stuffs, with the exception of WASAPI, are accessible through the CoreAudioDevices COM object accessible through the CoreAudioDevices property. This tutorial doesn't describe management of audio flow for playback and recording through WASAPI: this specific topic is described inside the tutorial How to manage audio flow through WASAPI.

 

If you open the "Sound" applet available inside the Control Panel of Windows Vista and higher versions, you will see on the "Playback" tab a list of audio rendering devices:

 

 

If you click the "Recording" tab you will see a list of audio capture devices:

 

 

For both "Playback" and "Recording" devices, respect to versions of Windows older than Vista (XP and earlier versions) devices are not seen as a single sound card having different set of input or output channels but each device is seen as a separate entity which is now called "audio endpoint device".

 

The new Core audio API distinguishes "Playback" devices from "Recording" devices by discriminating the direction of audio data flow:

 

 

Each audio endpoint device is displayed by the Control Panel with a set of information as seen in the following image:

 

 

After selecting a specific audio endpoint device and pressing the "Properties" button, a new set of tabs related to settings of the selected device will be displayed:

 

 

If supported by the sound card driver, you could find information about Jacks available on the sound card connector (channels mapping, location, size and color).

By clicking the "Levels" tab you would have the possibility to set the volume of the end point and also its "mute" state and channels balance:

 

 

The sound applet of the Windows control panel can be programmatically displayed through the CoreAudioDevices.DisplaySoundApplet method.

The coverage of Core audio API implemented by our component can be summarized in the following points:

 

Enumeration and status retrieval of audio endpoint devices

Volume, balance and muting management

VU-Meters of audio endpoint devices

Jacks description

Parts management

 

 

Enumeration and status retrieval of audio endpoint devices

 

Audio end point devices are enumerated through the CoreAudioDevices.Enum method: this method allows discriminating which devices need to be enumerated depending upon their current status: for example you could decide to omit from enumeration devices which are installed but disabled or devices which are installed and enabled but not plugged to a physical input/output device like the speakers or the microphone: as you may know, starting from Windows Vista sound card drivers can implement the so called "jack sensing" which allows the system to be informed if no physical input/output device is plugged-in.

 

During the enumeration, the component will internally create two separate lists, one for "Render" devices and one for "Capture" devices; each single element inside each separate list will be accessible through its zero-based index. The number of devices added to each list can be obtained through the CoreAudioDevices.CountGet method. Once you have the total number of devices for each list you can obtain further information through the following methods:

 

 

You can determine the current system default audio endpoint device through the CoreAudioDevices.DefaultGet method; as an alternative, the container application can be notified about changes to the system default device by catching the CoreAudioDeviceDefaultChange event. The possibility to programmatically set the system default device is given by the CoreAudioDevices.DefaultSet method.

 

In case a USB audio device should be added to the system, for example when an USB sound card is installed for the first time, the container application can be informed in real time by catching the CoreAudioDeviceAdded event.

When a device has been added to the system, it may still be reported as "Disabled" due to the jack-sensing feature that keeps a device disabled until a Microphone or the Line-In jacks are not physically plugged into the system; when the audio device should be set as "Enabled" or should be set as "Disabled" one or more CoreAudioDeviceStateChange events would be generated.

If the USB audio device should be uninstalled from the system, by physically removing the audio device and by uninstalling its driver from the system, the CoreAudioDeviceRemoved event would be generated.

After catching these events, as well as the CoreAudioDeviceStateChange event, it would be worth for the container application to perform a new enumeration through a new call to the CoreAudioDevices.Enum method in order to keep updated the lists of render and capture devices.

 

When the access to audio endpoint devices is no more needed, related resources can be released by calling the CoreAudioDevices.Free method.

 

 

Volume, balance and muting management

 

For each audio endpoint device, the application can retrieve/set the following type of volumes:

 

 

For all of the elements above, the container application can be informed in real time about changes made by the Windows Control Panel or by other applications by catching the CoreAudioDeviceVolumeChange event.

 

Volume applied to the various audio endpoint devices can be expressed in percentage linear values or in dB: a value in dB is based upon a logarithmic scale following the rules below:

 

 

from the "Sound" applet of the control panel you can decide which unit of measure adopt by clicking the edit box of the volume with the right mouse button: after the click the context menu with available units of measure will appear as seen on the screenshot below:

 

 

Using volume-related methods mentioned above you can decide the unit of measure of the volume obtained/set into the audio endpoint volume.

 

 

 

 

 

VU-Meters of audio endpoint devices

 

As we have seen in one of the images above, most audio endpoint devices have a related VU-Meter which allows detecting activities on the audio data flow. It's important to note that these VU-meters will not only report audio activities related to the container application but will report any activity performed by any running application on that specific audio endpoint device. When dealing with capture devices, it must be remarked that the VU-Meter will not act as a sort of monitor but will only report activities of recording/capture sessions performed by the container application or by other applications running inside the system: as an example, you can see VU-meters moving inside the "Recording" tab of the "Sound" applet of the Control Panel because the applet itself starts a capture session.

 

The container application can obtain peak levels for an audio endpoint device by enabling monitoring of VU-meter activities through the CoreAudioDevices.VuMeterEnableNotifications method. After enabling the monitoring, the container application will receive the CoreAudioDeviceVuMeterChange event each time a new peak value is detected; at this point peak levels can be obtained for the master channel trough the CoreAudioDevices.VuMeterMasterPeakValueGet method and for each single separate channel of the audio endpoint device trough the CoreAudioDevices.VuMeterChannelPeakValueGet method: as mentioned before, the number of available channels can be determined through the CoreAudioDevices.ChannelCountGet method.

 

 

Jacks description

 

The connector of a sound card has a set of jacks which can be used to connect input devices (for example a microphone) and output devices (for example one or more set of speakers). Modern sound card drivers allow enumerating all of the available jacks and, for each jack, can report a set of information like the location (for example rear or front panel of the PC), size (for example 1/8-inch or 1/4-inch), color (usually speakers are connected to the green jack and the microphone to the cyan jack) and channels mapping (for example, render devices configured for working with a 5.1 channel configuration can report if the jack is used for front speakers or rear speakers or center/subwoofer speakers).

 

The number of available jacks can be determined through the CoreAudioDevices.JackCountGet method; once the total number of jacks is available, you can obtain information for each single jack through the CoreAudioDevices.JackDescriptorGet method.

 

 

Parts management

 

A certain number of sound card drivers add the possibility to access subunits, also known as "parts", which allow defining further parameters related to volume settings or to muting settings; usually these subunits are accessible from the "Levels" tab of a specific audio device and can be available for both render and capture devices.

 

A typical example, for capture devices, is the microphone boost setting which allows applying an amplification of the audio data incoming from the microphone. When available, this setting can be accessed through the Control Panel in the following way:

 

 

 

By acting on the slider of the "Microphone Boost" setting, by default set to 0 dB, it will be possible to increase the amplification applied to the incoming audio data: note that there is a maximum range available and that increasing/decreasing of the value in dB is not linear but made up of predefined steps: the image above is for a Microphone whose maximum boost can be set to +30 dB and each increase/decrease step is of 10 dB: in this case the boost value could be only set to the following values: +0 dB, +10 dB, +20 dB and +30 dB.

 

Our component can act on the "Microphone Boost" setting using the following methods:

 

 

 

Another example, this time for render devices, is the possibility to set if and how the CD Audio, the Microphone and the Line In channel will work as playback devices. When available, these settings can be accessed through the Control Panel in the following way:

 

 

 

In the screenshot above we have remarked the "Microphone" part just because what will be said hereafter is related to this specific setting but it could be applied to all of the other available parts. By acting on the "Microphone" slider you can modify the volume of the sound incoming from the microphone and by clicking the small blue speaker's icon you can mute or unmute the channel; the "balance" button allows defining different volume levels for the left and right channel of the microphone.

 

Our component allows accessing all of the mentioned settings through the following methods:

 

 

 

 

Samples of usage of access to audio devices in Visual C++ 6 and Visual Basic 6 can be found inside the following samples installed with the product's setup package:

- CoreAudioDevices