Fixing unwanted cpu noise with audio interface. Please help!
November 30, 2012 5:39 PM   Subscribe

Please help me get rid of frustrating audio interface noise! I have a new pc and a presonus firestudio mobile audio interface. When I plug in the firestudio via firewire there is a pulsating sound and some buzzing sound.

When I just use the firestudio for playback of films or songs through my active monitors none of these sounds occur. They only occur when I try to record something through any of the inputs.

People tell me it is a ground loop problem. I have no idea how to mess with cables or anything to solve the problem. I don't think I can use a ground loop isolator because there is nowhere in the chain to put it as the chain only consists of cpu--->firestudio and i'm listening with headphones without monitors plugged in. Some people say I need to break the ground on the mains plug for my pc but I'm not sure how to do that either.

I tried a friends focusrite interface which was usb, it was even worse!

Any ideas? I will be eternally grateful to the person that helps me fix this!
posted by niruniru to Technology (10 answers total) 1 user marked this as a favorite
What happens if you play back through the device with it plugged into the computer? IE: it is plugged in, but you aren't using the connection.

As for solving the potential ground problem, you don't want to break the ground on anything. That is dangerous. What you need to do is make sure everything is grounded to the same common point. Plugging all the devices into the same power strip will usually suffice.
posted by gjc at 6:07 PM on November 30, 2012

It's literally only when I turn the gain up on either of the line/instrument channels that the noise starts. Any kind of playback with the firestudio connected is fine, just recording is ruined.

The pc is the only thing plugged in, the firestudio gets its power from the firewire through the pc. I tried plugging in the firestudio with it's own power cord anyway, just to see if that solved the problem, but even when it wasn't being powered solely by firewire the noise was the same. Whenever I plug things in they all go into the same adapter so i'm not sure what's going on.
posted by niruniru at 6:16 PM on November 30, 2012

Is it a desktop PC, or a notebook? If it's a notebook, does it have a three prong (grounded) plug that goes into the wall?

The problem sounds like the ground is floating (not actually connected to ground), meaning that the errant voltage on the ground/negative has nowhere to go and causes noise.

Other issues could be a firewire cable that doesn't have a grounded shield, or a firewire port on the computer that isn't grounded.

Does the noise change if you touch the ground of the inputs on the external box? If it does, then you (probably) definitely have an issue with a floating ground. That's about all I can think of.
posted by gjc at 7:05 PM on November 30, 2012

Ground loop (or such low quality unfiltered equipment you'll just need to deal with it). Simple as that.

To fix it, try three things (one of these most likely already applies):

1) Plug all the devices involved into the same power strip (shortest possible path to shared ground).
2) Plug each device involved into an entirely separate circuit (relative to your breaker box) (longest possible path).
3) Let each device float - Plug them all in via 3-to-2-prong adaptors, aka cut off the third prong (no possible path).

#2 doesn't really count as convenient, but if it works, you can probably narrow the problem down from there to something workable.

#3 doesn't count as especially safe, but (probably) won't kill you for the purpose of debugging your connections; and if it works, you can always give one or two devices a "true" external "Earth ground" rather than relying on the third prong.
posted by pla at 7:47 PM on November 30, 2012

Okay so I can assume it's a ground loop that helps at least thanks guys. I'm just gonna cut the third prong off my mains supply and hope it works.

If I want to lift the ground on the firestudio box how would I do that? Considering that it's powered by firewire through the pc and not by it's own plug, I'm assuming I have to do something with the firewire cable itself?
posted by niruniru at 2:29 AM on December 1, 2012

A long shot, but....

My Focusrite Saffire absolutely HATES my mobile phone. If it is up on the desk where my Saffire is, I get a constant buzzing in my headphones.

If you've got anything electronic up there, try process of elimination to see if that's it.
posted by kuanes at 3:12 AM on December 1, 2012

Well, I hope I'm not too late but please please please don't actually CUT anything - if you want to try lifting the ground use a 3-to-2 prong adapter like this.

kuanes has an excellent point about other electronics in the vicinity possibly causing this noise.

Are there any fluorescent lights in use in the room? Those can cause all kinds of noise.

Do you have anything else (router, lamps, clocks, etc.) plugged into the same circuit? Try unplugging them one at a time to see if the buzz goes away. Note that different wall outlets can be the same circuit.

Does anything you have plugged into the same circuit use a wall wart? Buzz can be caused by cables running past one of those. Or, if the wall wart has both prongs the same size, try plugging the wall wart in the other way around.

If I'm reading you right, the problem only shows up when you plug something in to the inputs & try to record, yes? So my first guess is something's up with whatever instrument or microphone you're plugging in. Which is what? Some more detailed info about your signal chain would be helpful.
posted by soundguy99 at 7:55 AM on December 1, 2012

i've tried all those things soundguy99. the adapter won't work sadly because i'm in the uk where all sockets are 3 prong as you may know.

tried my firewire firestudio on its own in the wall mains and still a kind of noise so i'm giving up on that and just trying to make the usb focusrite work.

So i have a multi plug adapter in the wall mains, with only my pc and visual monitor plugged in to it. I connect a focusrite via usb and there is a buzz which is recorded when I try to record, i've tried different instruments and cables to no avail, so i'm right now just using a working guitar via a working guitar lead when checking it. Playback is fine with other media, its just when playing back my own recordings or making new ones the buzz happens. I'm listening with headphones, so no monitors.

Would this work? It could go between my cpu and audio interface usb and break the ground loop?

If i set up some monitors and put one of these

between the audio interface and monitors, would that break the whole ground loop or just stop the sound between the monitors and audio interface?

I'm sorry i'm an idiot.
posted by niruniru at 12:37 PM on December 1, 2012

Ah, sorry, I didn't realize you were in the UK. I don't know enough about the UK electrical system to give you advice on that end of things.

Except - supersimple idea - by "multi plug adapter" you mean what's also called a "power strip?" Like this? Try using a different one, if you've got one available. Here in the US at least they're all pretty much crappy Chinese junk, so it's not uncommon to get one that's got ground problems.

The fact that you've got no noise problems playing back media really makes me think that the problem lies somewhere in the front end of your signal chain. What kind of guitar do you have? If it's a Fender or another kind with single-coil pickups, those are inherently more likely to be noisy, although humbucker-equipped guitars aren't always totally immune. Sometimes the only way to fix this is to physically be in a different place; stand up, move a few steps, turn your body, see if the buzz goes away or is reduced. It's also possible your guitar isn't grounded correctly internally - a way to test this is to connect a piece of wire from the bridge of the guitar to the sleeve of your guitar lead, see if the buzz goes away.

So while the Olimex USB-ISO bit you linked to might help, first I would try an Ebtech Hum Eliminator or the similar Behringer device between your guitar and either presonus piece.

They're essentially the same thing as the Maplin piece you linked to - they're all basically isolation transformers - but the Maplin piece, if you set it up as described between the audio interface & some speakers, would only eliminate ground problems caused by that connection, which is not your problem now.

P.S. You are not an idiot. NO apology necessary. At worst, you are inexperienced, and we've ALL been there. Plus, ground buzz problems are seriously the devil's own handiwork, often solved only by teeth-grinding painstaking trial-and-error, or dumb luck. Trust me on this one. Cheers.
posted by soundguy99 at 7:43 PM on December 1, 2012

I've just tried a power strip that works for someone else, the buzz was still there. The buzz, though only turning up when trying to record, is the same no matter what instrument is in there, i've tried a few synths and guitars with a few cables, no matter where you move the instrument it stays the same.

I'm almost certain this is the pc causing the trouble, when my brother built it maybe he put some components close together that shouldn't be, or maybe I need to do something with the motherboard, I have no idea! Could it be things like that?

I'm going to try breaking the ground prong on a plug today, if that works I'll get the olimex thing rather than leave myself at risk of electric shock all the time, but just so I can clarify whether it's a ground loop issue i'm gonna give it a try.

How come nobody on the whole internet seems to have a problem with a pc--->interface--->headphones setup? is that not enough components for the average ground loop to occur? I'm so confused why i seem to be the only one on the internet that has this problem without using monitors in my setup it's weird!

thanks so much for your time on this annoying issue and the vote of confidence
posted by niruniru at 5:09 AM on December 2, 2012

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