All methods in your link I tried such as disable unused IRQ, assign individual IRQ to different DE410P, dedicate different interrupts to different CPU. However, quality only a little improve when number of call is large.
i have some tips ,please have a try
If you are running an IDE hard drive please verify that you are using DMA mode with a UDMA setting of no lower than 2 or higher than 3. UDMA mode 2 is ATA33. UDMA mode 3 is ATA44. This can be done using hdparm.
We suggest using "hdparm -d 1 -X udma2 -c 3 /dev/[IDE Device]". You can check the status using "hdparm /dev/[IDE Device]" and "hdparm -i /dev/[IDE Device]". If you make modifications to your IDE hard drive settings they will only be kept until you reboot. "
Be sure to try kernel 2.6 too, it has better I/O performance than 2.4 kernels.
Don't use X on your asterisk server.!
-Disable the framebuffer.
There is no improvement after I set /sbin/hdparm -d 1 -X udma5 -c 3 /dev/device and unplug one DE410P from the system. That means sound goes worse when number of call greater than around 60-70 at a same time. Any more suggestion? :'(:'(:'(