Using a USB Headset (Microsoft LifeChat LX3000) with Unity's default volume control in Ubuntu 14.04 LTS, the speakers suddenly mute sound when I turn the system's main volume below a certain threshold. The threshold varies, but is about 25% to 33% of the scale available. I would expect sound to gradually become quieter and quieter until reaching the muted state at zero volume instead.
How can I get that (IMHO more intuitive) behaviour? What causes the early muting?