Bypassing Windows Kernel Audio Mixer

(a.k.a. KMixer)

Due to its basic purpose to process the audio signals, i.e. to set their levels, mix them and convert between bit depths, sample rates and formats, as long as a PC is used for playback only, there is a strong reason to bypass KMixer. This is because in this case the actual requirement is to preserve the data integrity or, in other words, the goal is so-called bit perfect output. Though with some care it is still possible to achieve this goal with KMixer included (it is most important to make sure to set the Wav slider to the max position and balance to the center), a much safer option is to bypass it.

To get rid of KMixer we recommend using Foobar2000 and if you accept this recommendation, we also recommend following these steps. The procedure applies to a USB DAC.

1. Download and install Foobar2000.

2. Download and install ASIO4ALL.

3. Download ASIO support for Foobar2000. Unzip the file and copy it to the Foobar2000 components folder (probably c:\Program Files\foobar2000\components).

4. (Re)start Foobar2000.

5. In the Foobar2000 main window, go to File > Preferences. In the Preferences window, under Playback > Output, you now should have ASIO Virtual Devices. Select it and click the button Add New.

6. In the ASIO Virtual Device Editor window that pops up now, map USB Audio Device Channel 1 to the left and USB Audio Device Channel 2 to the right channel. Click OK.

7. You'll return now to the ASIO Virtual Devices in the Preferences window. Go one level up, to the Playback > Output and from the Output Device drop down menu choose ASIO: ASIO4ALL.

8. Click Save All and then Close.

9. Now it may (and may not) be needed to restart the Foobar2000.

That's all.

To check whether you were successful in this or not, open the Mixer. Make sure that you choose USB Audio DAC and not some other device you may possibly have in the system; you can switch between Mixer Devices using the Options > Properties menu in the Mixer window. If all is done well, moving the slider Wave should have no effect on the playback volume.

At the time of writing this article (November 2006) the latest version of Foobar2000 is 0.9.4.1 and the latest version of ASIO support is 1.2.4. They appear to work flawlessly under Windows XP and with ASIO4ALL version 2.6. The Direct Kernel Streaming support file which also can be downloaded from the Foobar site may be the alternative way to bypass KMixer but experience showed that it has less chances to work than ASIO file.

As for the Foobar2000 itself, please make sure that the volume control available within its "Playback" menu is set to the maximum (as is by default) and all the DSP utilities are turned off.


Added in April 2011:

Some newer versions of ASIO4ALL appeared to perform resampling by default setting, and it was exactly what we wanted to avoid here. So, to ensure that the ASIO4ALL alone is also set appropriately, please open its "Off-Line" control panel, and make sure that "Always Resample 44.1kHz <-> 48kHz" box is unchecked. For the similar reason, "Force WDM Driver To 16 Bit" should be unchecked too, though this one likely won't have any effect (please refer to ASIO4ALL Instruction Manual for further information).

While you are there, you can also set the ASIO Buffer Size to the maximum. It will increase the latency somewhat, which is of no interest here, but it will also help eliminate possible problems with too short buffer, which sometimes (very rarely in practice though) manifest as pops and clicks during the playback.


Copyright © 2006, 2011 Audial