z_ALSA.txt

To compile for native ALSA under Linux you must
have these files on your system:

/usr/lib/libasound.so
/usr/include/alsa/asoundlib.h
Under Debian they come with the package libasound2-dev

The version number in /proc/asound/version must 
be 1.0.12 or higher.

The configure script tests for presence of a modern enough
version of ALSA.


Configuring ALSA for realtime priority
******************************************************************
Add these lines to  /etc/security/limits.conf
@audio -       rtprio          99
@audio           -       memlock unlimited

Configuring default soundcards / stopping soundcards from switching 
*******************************************************************
Note: This section assumes that you have installed each soundcard
properly. 

      * In a shell, type cat /proc/asound/modules 
        
      * This will give the the name and index of each soundcard you have
        currently. Make a note of the names, and decide which one you
        want to be the default card. 
      * Now type sudo nano /etc/modprobe.d/alsa-base.conf 
        If the file does not exist, just create it. 
        
      * At the very end of the file, add the following (assuming you
        have 3 cards with module names A, B and C and you want to have
        them in the order CAB) 

options snd-C index=0
options snd-A index=1
options snd-B index=2

(From : https://help.ubuntu.com/community/SoundTroubleshooting  )

***********************************************************************
Comment out any statement that might give one of your drivers index -2.

# Prevent abnormal drivers from grabbing index 0
options snd-bt87x index=-2
options snd-cx88_alsa index=-2
options snd-atiixp-modem index=-2
options snd-intel8x0m index=-2
options snd-via82xx-modem index=-2
options snd_ice1712 index=0
options snd_ens1371 index=1
options snd_intel8x0 index=2


Configuring multiple USB soundcards
***********************************
If one uses multiple USB soundcards, the indices for these soundcards
should be coded as follows:

options snd-usb-audio index=3,4

and not 

options snd-usb-audio index=3
options snd-usb-audio index=4
(in this case the second line would override the first )