[Eleazar]

Problem:
I was having an issue with interference, not loud but slightly noticeable, anytime I used the sound card while the video card or IDE interface were being actively used at the same time. It mostly only happened with the headphones, when using external speakers it was even less noticeable. When using the headphones at comfortable listening levels I couldn't hear the interference but whenever I would reach a quiet scene in the game or when music wasn't playing I would hear the constant noise. When I only used the computer for listening to music any noise was completely below perceptibility. One more thing to note, whenever I used the sound card, video card, and IDE device actively all at the same time, some very fun things began to happen. Fun as in, complete system freeze ups and a high pitched screeching sound coming from my sound card. It was an amazing XFi experience!!!!!!

Solution:
I had to disable APIC in the BIOS and do a repair installation of Windows XP(I hate repair installs), it actually worked out well since I had just reimaged the PC anyways, so very little inconvenience came from it in reinstalling software and drivers. The repair installation was necessary since all IRQ assignment was being handled by the APIC driver interface to the BIOS. I would have to uninstall this driver and switch it to Standard PC or default ACPI. The problem is, none of my devices would be recognized on boot up if I did this. The only way to have Windows properly recognize your devices is to select or by default have Windows select the desired driver at installation of the operating system.

What is APIC?:
APIC allows you to have an extended range of IRQs above the default 16 increasing to 24. It is something only multiprocessor PCs has. Unfortunately, some vendors have very poor drivers that do not play very well with APIC. Ideally the extra IRQs would ensure less overlap of IRQs and more devices could be distributed to the available open IRQs. However, under APIC my video card, sound card, IDE, and more devices were all on the same IRQ. So much for less overlap of devices. Normally this overlap wouldn't be too much of a problem as long as all the drivers were optimally programmed with APIC in mind. This certainly wasn't the case, and from what seems to be the consensus in the IT community, you have to get rather lucky for it to happen. In fact, many people say to disable ACPI altogether and handle IRQ's assignment through the BIOS or manually(ACPI is distinct from APIC, though they are somewhat related).

This actually sucks, this is something Creative needs to fix in their terribly horrendous drivers. APIC has better interrupt handling and improved performance for multiprocessor setups(which I have). Given the tradeoff though, I would choose disabling APIC every single time.

Important Note to others:
If when you use USB devices you hear clicks when you move your mouse wheel or other specific inputs on a usb device, this is most likely due to a poorly programmed driver and its interaction with APIC. You do not really need to use APIC if you don't have a multiprocessor system.

Though I would share my finding with everyone here. If you would like to know how to disable APIC yourself and do a repair installation, I am not going to regurgitate information. Simply do a Google search, there is a wealth of easily accessible information on this topic.

 

[Jodiuh]

I'm bumping this for good info. I'm also curious if Vista/Windows 7 or another board would take better care of APIC here. Also, I remember having a pretty good time w/ XP, my P5B, and the X-Fi Xtrememusic a couple years ago. FWIW, I'm on a Maximus, W7, and will have a Forte soon. I'll update my post w/ pics of the IRQ table.

ATI or NV?

 

[Eleazar]

Nvidia. The only drivers that could be causing the issue would be from the XFi Forte which I believe are based off Creative's. Nvidia has very good drivers and has some of the best software engineers in the biz, as well as Intel who would be the other drivers on the same IRQ(all chipset related). It should be noted that my drivers are always up to date. It is well known that other sound cards have this issue, even onboard audio.

To go off topic:
There is a fairly good review of the XFi forte over at EB, don't know if this has been posted yet. The review speaks of interference and noise on the headphone amp, I did not experience this, even at silent dB levels. This could be due to my high quality motherboard with a very good power supply. I would expect EB to have good quality as well, I don't know enough about their specific motherboard model and power supply.
Elite Bastards - Auzentech X-Fi Forte 7.1 PCI Express sound card review

Switching from the Creative XtremeMusic to the XFi Forte I noticed a difference in SQ, specifically clarity. The headphone amp portion is neutral and doesn't take away or add anything. I did a listening test of the amp vs. unamped in Sinegen and there was no noticeable change in the frequency response to my ears. The A900's still had the same large peaks and dips, which I am unfortunately all too familiar with. Initial equalizing has helped, it is definitely less fatiguing now. Once I am done fully tweaking the equalizer I will post my results in the headphone equalization thread.