AVS Forum banner
1 - 6 of 6 Posts

·
Registered
Joined
·
3 Posts
Discussion Starter · #1 ·
Hello,


I've searched around all morning without much success, so I thought I'd visit a forum of experts and see if anyone can help me. My apologies if this is the wrong forum, I wasn't sure where to post.


I have a modest "home studio" set up for music production work. It's really just a bit of fun, but it's getting more serious and I've "invested" in some decent active stereo monitor speakers (KRK Rokit5 G2s) and the matched subwoofer.


Here's how I have things set up:
  • subwoofer connected to Windows PC via a Sound Blaster X-Fi "XtremeGamer Fatal1ty Pro Series FPS" (what a name). The cable is a simple unbalanced 3-contact mini-jack (3.5mm) at the sound card end, to a stereo RCA pair into the subwoofer. It's about 2 metres long.
  • the soundcard is a PCI-Express card (I think), located in the bottom-most slot on my motherboard (as far away as possible from my video card). Actually it might be PCI, but it's probably not important.
  • the video card is a fairly grunty Nvidia 8800GTX.
  • each of the two monitors connect to the subwoofer via a 1 metre mono balanced cable with XLR connectors, per monitor.
  • the sub and both monitors are actively powered - they have their own amplifiers.
  • the sub and both monitors draw from the same AC mains supply as the computer, which is also on a UPS (uninterruptable power supply).
  • If I reduce the monitor gain the noise decreases as you'd expect, but I lose the maximum volume level as well. I try to have the sound card as 'hot' as possible.


I used a sound level meter (with pink noise, etc) to calibrate the monitors and sub to about 90 dBC at maximum sound card output level. This gives me a good dynamic range to play with and keeps the sound card output level fairly high.


Unfortunately I have a serious noise problem. It appears that the system is picking up some sort of electrical "clock" noise from the PC, or somewhere. It's not a uniform noise - it's more like an electronic squeal, and it seems to be correlated with activity on my PC. For example, if I drag windows around, fire up a big application, run a 3D game, or perform significant CPU work, there's a high-pitched noise in the monitors. It's quite loud and it sounds very 'electronic'. It cuts in and out often, but it's always present. It's not overly loud but it is very annoying. It's present even when the video card is not doing anything 3D - e.g. a static 2D Windows desktop.


When the sound card is muted, the volume of this noise does not change at all. It seems to be independent of the digital audio into the DAC (as you'd expect).


What I suspect is that the analog cable to the subwoofer is picking up noise somewhere after the DAC. I'm not sure if it's picking it up inside the sound card, or just after it leaves the PC case.


Obviously if I unplug the cable to the sub, it picks up 50Hz (AC mains frequency) and the sub hums. The noise I described is no longer present.



In order to address this problem, I've considered three alternatives:
  1. cabling
  2. external USB audio interface
  3. external SPDIF DAC


Cabling: the cable I am using between the PC and the subwoofer is a pretty standard two-wire twisted-pair + shielding, where the shielding is used as the ground (shared between both L & R) and each wire carries a single unbalanced signal for the L or R channel. Because the output port on the sound card is simply a 3.5mm stereo socket, I think my options here are limited. I'm not aware of any way to use a balanced output with this sound card. The sub has a ground-lift switch but this doesn't make any difference.


The sound card I have apparently has a very good mid-range DAC incorporated, so it seems a shame to bypass this in some way, but if it's the only solution then I've looked at the following two options:


External USB audio interface: this is appealing since if I get the right one, I could use it on my Macbook too, and use it for audio recording. However my analysis of the market has shown that all reasonably priced USB interfaces have significant design problems or unhelpful power requirements and I'm really at a loss to find a unit that would suit me. I've also heard that the ground line over USB can easily transfer noise as well.


External SPDIF DAC: with the optional Creative Digital I/O Module, I can get SPDIF optical or electrical out to an external DAC and use this to generate the audio signal for my speakers. This might isolate the analog part from the electrically noisy part of my system.


Unfortunately both of these solutions may leave me in a situation where the new DAC I use may be inferior to the sound card's DAC, which has a really nice sound to my ears. It seems a shame to bypass this when the card has a perfectly good DAC for my needs.



Does anyone know of a way I can resolve this problem? Ideally, is there a different way I can connect the sub to the sound card that might help reduce this noise?

I'd like to know if there's anything I can do with the cabling to help mitigate the problem.


Here's one crazy idea - as what I want is just a stereo signal, is there some way I can use the multiple Surround outputs of the sound card to create a balanced signal? Perhaps that might help reject some of the noise?
 

·
Registered
Joined
·
6,946 Posts
Be sure you have muted all unused inputs/outputs on the sound card.
 

·
Registered
Joined
·
3 Posts
Discussion Starter · #4 ·

Quote:
Originally Posted by MrBobb /forum/post/16978100


Cheap thing to try... move the card to another PCI slot. May have to uninstall drivers first, move the card, reinstall drivers.

Good idea, I'll try that. I'll also try removing the UPS to see if it makes any difference at all.


Quote:
Sidebar: Each spkr has it own power? like separate power cords into ea. sprk? That's crazy, from an aesthetic point of view.

Yes, that's right - separate power cord into each speaker. I'm not exactly sure why it's done that way, but I do know that KRK designed these monitors for different configurations, so you might have 2, 4 or even 6 (if you're rich).


I'm fairly sure it's not the speakers that are causing the problem, because they sound perfectly fine on a different audio source (like an mp3 player).

Quote:
Originally Posted by whoaru99 /forum/post/0


Be sure you have muted all unused inputs/outputs on the sound card.

I hadn't thought of that - easy enough to try. Do you know why this might be an issue? Some sort of cross-talk?
 

·
Registered
Joined
·
1,495 Posts

Quote:
Originally Posted by whoaru99 /forum/post/16978485


Be sure you have muted all unused inputs/outputs on the sound card.

+1


You might also want to mute all except the one you are currently using.
 

·
Registered
Joined
·
3 Posts
Discussion Starter · #6 ·

Quote:
Originally Posted by shane55 /forum/post/16982515


You might also want to mute all except the one you are currently using.

I tried this last night (muting rear L/R, line in, etc) but it didn't seem to make any difference at all unfortunately.


Changing the output volume does not affect the noise level at all, so it seems to me it's being picked up after the final gain stage. Is the output level control on this card pre- or post- DAC? (i.e. digital gain prior to DAC, or analog amplifier after DAC?).


I'm going to try moving the card to another slot when I get time.
 
1 - 6 of 6 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top