Use the mixer to understand and tweak the different volume levels your sound card provides.
Almost every audio device you encounter has some way to control the volume, whether through a volume knob on a radio, the remote control on a television, or the series of controls on a sophisticated sound board. To control the sound on a Linux system, you use a mixer program. Even though the purpose of the mixer—to change the volume—is simple, often the sheer number of options the mixer provides can prove daunting to new users: it's not as simple as adjusting a single master volume control. Also, Linux has two different systems for sound, OSS and ALSA, so there is additional complexity that is not immediately obvious. In this hack, I cover a few mixer programs and describe the differences among Master, PCM, and the other major volume controls.
You can launch a mixer program a few different ways. If you use the GNOME or KDE desktop environments, the quickest way to access the mixer is to click the speaker icon on the desktop panel. Windows users will find this applet similar to the speaker on the Windows taskbar. A single click on the icon lets you change the master volume (see Figure 2-1); a right-click shows you various options for the mixer applet. For common volume control, you may only need to access the master volume. To access all of the advanced volume controls, double-click on the applet to launch a complete mixer.
Figure 2-1. Panel Mixer applet ...