Generic loopback driver (PCM)

modulename: snd-aloop.ko

configname: CONFIG_SND_ALOOP

Linux Kernel Configuration
└─>Device Drivers
└─>Sound card support
└─>Advanced Linux Sound Architecture
└─>Generic sound devices
└─>Generic loopback driver (PCM)
In linux kernel since version 2.6.37 (release Date: 2011-01-04)  
Say 'Y' or 'M' to include support for the PCM loopback device.
This module returns played samples back to the user space using
the standard ALSA PCM device. The devices are routed 0->1 and
1->0, where first number is the playback PCM device and second
number is the capture device. Module creates two PCM devices and
configured number of substreams (see the pcm_substreams module
parameter).

The loopback device allows time sychronization with an external
timing source using the time shift universal control (+-20%
of system time).

To compile this driver as a module, choose M here: the module
will be called snd-aloop.

source code: