From the ALSA wiki |The FAQs have been reorganized. The new
location of this question is Mixer| What is a Mixer? A mixer is
a device that controls the sound inputs and sound outputs on a
soundcard. A mixer requires both hardware and software
components. The hardware mixer is part of the electronics inside
a soundcard. A software mixer is some software which provides a
user interface for controlling the hardware mixer. Examples of
software mixers include: A software mixer does not control the
hardware mixer directly; the ALSA sound driver is always an
interface between the software mixer and the hardware mixer.
This is because different soundcards have different interfaces
to their hardware mixers. The purpose of the ALSA sound driver
is to provide a standard interface for controlling the different
hardware-mixer interfaces. This means one software mixer can
work with many different soundcards. Typical examples of mixer
controls are: Master Volume (L,R) Bass Tone (L,R) Treble Tone
(L,R) Line Input (L,R) PCM Vo