ubuntu usb sound card sometimes recognized and sometimes not at boot

Question

I have a linux ubuntu 12.04 server machine which works with an usb sound card. When rebooting the machine, sometimes the usb sound card is recognized and sometimes not, I cannot figure out a reason for this. I understand when the sound card is recognized because when I issue the command:

cat /proc/asound/modules

I can see listed or not the line snd_usb_audio.

Analyzing the /var/log/kernel.log I can see sometimes (when it works)

kernel: [    6.236564] usbcore: registered new interface driver snd-usb-audio

and other times (when it is not recognized and listed):

kernel: [    7.126855] snd-usb-audio: probe of 2-1.2:1.0 failed with error -5
kernel: [    7.126876] usbcore: registered new interface driver snd-usb-audio

Does anybody know how to ensure that the usb sound card is always recognized?

Solution

Ok this solved the problem:

1) blacklist the integrated audio card

sudo nano /etc/modprobe.d/blacklist.conf

and add the line

blacklist snd_hdma_intel

where the name snd_hdma_intel is retrieved after issuing the command

cat /proc/asound/modules

(for example the output for me was)

0 snd_hdma_intel
1 snd_usb_audio

2) edit the following file:

sudo nano /etc/modprobe.d/alsa-base.conf

comment the lines regarding snd-usb-audio this way:

#options snd-usb-audio index=-2

3) just reboot