I just got this question again.

In XP, the steps to mute one of the channels in the OS was very few. The Left/Right balance slider is simply a click away from the volume icon (if I remember correctly). But in Vista, that control is more steps away from the users. Obviously, we thought not many people would need that control at all. 

A lot of people I know obviously still watch VCDs that are published for multiple areas. For example, the left channel of the VCD would play the Mandarin track and the right channel would play the Cantonese track, both for the same movie. My friends, my parents, and my friends' parents all asked me how to mute the Mandarin channel. So here you go. This applies to Windows Vista and beyond.

  1. Right click on the speaker icon at the lower right corner.
  2. Choose "Playback Devices to open Sound Control Panel.
  3. Right click on the "Speakers" or any device with the green check mark. (The green check mark indicates the default device that is used for streaming audio currently.)
  4. Choose "Properties" to open up the device property pages.
  5. Choose "Levels" tab to change the volume levels.
  6. Click on "Balance", this brings to to the channel volume setting UI.
  7. You can adjust the Left and Right balance. Drag the slider all the way to the left to mute or drag it to the right to make the channel louder. If you are using a multichannel speaker (like 5.1 speakers)
    then you will see more sliders.

I'm not a UX expert, and I don't know if we made the right tradeoffs here. However, I wish we had noticed how ubiquitous this scenario is in certain regions. We probably could consider mitigations such as making a localized version of Windows Media Player that has easier access to the channel volume?