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Alternative A2DP Driver FAQ

Installation

Operating System
Windows 10 Version 1903 to Version 21H2 (x64 only), Windows 11 Version 21H2 (x64 only)
Bluetooth Stack
Windows 10/11 inbox Bluetooth Stack
  1. Download the installer from the download page.
  2. Double-click on the downloaded installer file and follow the instruction.

After installing the package to your PC following the "How to install the Alternative A2DP Driver package?" section, all of your Bluetooth audio devices are still controlled by the Windows inbox A2DP driver.

The next step is installing the Alternative A2DP driver to your audio device(s).

  1. Select the device in the left pane.
  2. Select "Alternative A2DP Driver" from the "Device Driver" drop-down list.
  3. Click on the "Install" button.
  1. Navigate to Windows Start Menu > Settings > Apps > Apps & features.
  2. Look for "Alternative A2DP Driver" in the App list.
  3. Click the button, then select "Uninstall" from the list.

After the beta version expires, your Bluetooth headphones will connect to your PC, but you don't hear any sound from them. You will also see an expiration message in the app.

At this point, you have the following options:

  1. Uninstall the entire software package.
  2. Update to the newer version, which hasn't expired yet.

Limitations and Known Issues

The current version (version: 0.7.1) has the following limitations.

  • Does not support the "Absolute Volume" feature.
  • Supports SBC CODEC only.
  • Error recovery is minimal.
  • If something goes wrong during the CODEC configuration process, which usually happens when the device is connected, Windows recognizes the device is "connected", but the device does not work as an audio device.

    If this happens to you, please turn off the device, wait for the OS to recognize the device's disconnection, then turn it on and attempt reconnection. If the problem persists or occurs frequently, please send feedback using the in-app feedback page.

As you can see in the app's user interface, there are many options for A2DP CODEC configuration. All devices that claim compatibility with A2DP specification have to implement those options properly, and the manufacturers should test whether those options work before they ship the devices.

But, historically, PCs and phones used only one setting (44.1 kHz sampling frequency, Joint Stereo, block size 16, loudness allocation, eight subbands), and the device vendors never tested their products with other settings. I suspect many of them don't even have a way to test their devices. So, you are probably the first person to try different configurations, and there's a good chance you will find out they are not working.

If you encounter the issue, please try the following:

  • Click on the "Restore Default Parameter" button and load the most commonly used parameters.
  • Turn the device off, then on, and reconnect.
  • Check if the device is working correctly.

If the device works with the default parameter and has a problem with others, it's most likely an issue with the device. Please DO NOT report such an issue unless you have a good reason to believe that this is a driver issue. When you report such an issue, please include:

  • The reason why you think/suspect this is a driver issue, and
  • Mention that you've read this FAQ.

This will help your feedback to get the proper attention.

This problem occurs because the Windows inbox A2DP driver refuses to unload when it is nicely asked to unload.

Unfortunately, we cannot change the behavior of the Windows inbox A2DP driver, but instead of rebooting the system, you can shortcut the process by toggling the Bluetooth radio off and on from the Windows Bluetooth control panel. It will force the Windows inbox A2DP driver to unload and allow the Alternative A2DP driver to take over.

Usage Examples

One of the reasons why you hear the stuttering/choppy noise is the high rate of data re-transmission between your PC and headphones due to the poor radio condition. When there is too much re-transmission, some media packets are not received by the headphones on time, and as a result, you will hear stuttering/choppy noise.

One of the solutions for this issue is to reduce the amount of media data that needs to be transmitted (by slightly decreasing the audio quality). Please move the "Bitpool" slider to the left (decrease the bitpool value) while you are playing audio and see if the noise is reduced.

There are two ways to increase the bitrate of SBC CODEC.

Method 1: Use Dual Channel mode instead of Joint Stereo mode — Guaranteed to work by the A2DP specification, but not so efficient

The first way is to use the Dual Channel mode instead of the commonly used Joint Stereo mode. Due to the peculiarity of how the A2DP specification is defined, a device that supports maximum bitpool N (this bitpool number is assigned to combined left and right channel) is required to support the same maximum bitpool number N in Dual Channel mode, where each channel is encoded into that bitpool N. So, the resulting bitrate will double if you use the Dual Channel mode. Sounds too good to be true? Of course, there is a catch. Because the Dual Channel mode encodes the right and left channels independently without taking advantage of the correlation between the channels, it cannot compress the data as efficiently as the Joint Stereo mode. For example, when you compare Joint Stereo mode at bitpool 2 * N and Dual Channel mode at bitpool N, they yield (almost) the same bitrate, but the Joint Stereo will sound better.

Please also note that if you switch from Joint Stereo to Dual Channel without changing the bitpool number, the resulting bitrate may be too high to transmit stably due to the error and re-transmission.

Method 2: Use Joint Stereo mode with a higher bitpool number — May work with many, but not all headphones

The other way to increase the bitrate is to simply increase the bitpool number while still using the Joint Stereo mode. Most devices limit the maximum bitpool number to 53 (or even lower), but some allow a higher bitpool number. If your device is one of them, you can safely increase the bitpool number (slide to the right) and see how far you can go.

For the devices with a maximum bitpool number of 53 or lower, the Alternative A2DP Driver provides an option to override (ignore) that limitation and let you try a higher bitpool number.

WARNING: There is no guarantee that this option works (and, in theory, there is even a possibility that it might cause damage to your headphones if their firmware is poorly written), but if you want, you can try the "Override device's Max Bitpool limitation" option at your risk.

Windows inbox A2DP driver supports only 44.1 kHz sampling frequency for SBC CODEC. So, if you listen to the contents encoded with 48 kHz sampling frequency, you are forced to down-sampling.

On the other hand, Alternative A2DP makes all sampling frequencies supported by your audio device available to the media player app. So, if the media player app can dynamically switch the sampling frequency based on its source, you can eliminate the audio quality loss due to the down-sampling.

Please follow the instructions below to enable this feature.

Alternative A2DP Driver setting

First, you need to configure the Alternative A2DP Driver to use both 44.1 and 48 kHz sampling frequencies.

It is recommended NOT to enable other sampling frequencies (i.e., 16 and 32 kHz) unless you really want to use them.

(optional) Verify the above setting is working

  1. Connect your Bluetooth audio device to your PC.
  2. Type mmsys.cpl into the Windows search box and hit ENTER to start the legacy Sound control panel.
  3. Select the Playback tab (which should be selected by default), look for the Bluetooth audio device, and double-click on it to open the Headphones Properties dialog box.
  4. Select the Advanced tab and check the drop-down list in the Default Format section. You should see "2 channel, 16 bit, 44100 Hz (CD Quality)" and "2 channel, 16 bit 48000 Hz (DVD Quality)". If you do, the driver is working fine.
  5. NOTE: This drop-down list is supposed to let the user select the audio stream format when this audio device is used in the Shared Mode, but it does not seem to be working on recent Windows 10 and 11. The cause is unclear at this point, but it seems to be an issue with Windows 10 and 11.

Media player app setting

The media player app has to support the Exclusive Mode (and please note that not all media app does) so that it can change the sampling frequency of the audio device. (When the device is used in the Shared Mode, the sampling frequency is controlled by the System Mixer, and media player apps cannot control it.) Please also note that, by definition, in the Exclusive Mode, your audio device is exclusively controlled by that media app, and the output from other apps (including the system sounds) cannot be played on the same device.

Following are some of the apps that support Exclusive Mode and how to configure them for the dynamic sampling frequency change.

Kodi

  1. Navigate to the "Settings" > "System" > "Audio" page.
  2. Set the settings level (at the bottom-left corner) to "Advanced" or above.
  3. Select "WASAPI: Headphones (...)" or "WASAPI: default" for the "Audio output device."
  4. Select "Best match" for "Output configuration" (this setting item does not show if the setting level is "Basic" or "Standard").

MPC-BE

  1. Navigate to the "View" menu > "Options ..." to open the "Options" window.
  2. Select the "Audio" node in the left pane.
  3. Select "0. MPC Audio Renderer" for the "Audio renderer" drop-down list.
  4. Click the "Properties" button to open the "Properties" dialog box.
  5. Select "Exclusive" for the "WASAPI mode" drop-down list, and enable the "Allow bit exact output" checkbox.

MPC-HC

  1. Navigate to the "View" menu > "Options ..." to open the "Options" window.
  2. Select the "Playback" > "Output" node in the left pane.
  3. Select "MPC Audio Renderer" for the "Audio Renderer" drop-down list.
  4. Select the "Internal Filters" > "Audio Renderer" node in the left pane.
  5. Click the "MPC Audio Renderer Settings" button to open the "Properties" dialog box.
  6. Select "Exclusive" for the "WASAPI mode" drop-down list, and enable the "Allow bit exact output" checkbox.

General Information

Here's the list of the links to some of the information.