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What exactly IS that laptop noise, and how do I fix it?

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What exactly IS that laptop noise, and how do I fix it?

Postby lewk » Mon Jan 23, 2012 9:40 am

Hi all,
So I've got a couple of HP NX7300 laptops I use for our school shows, through M-Audio fast track pros, for running sound effects. On the whole, they are great. But if the laptop is plugged in, more often than not there is a computer noise sent to the PA. It's not a hum, more of a chatter, and if you move a window or do anything then it gets louder, or more active. It's really frustrating, I assume it's something to do with the power going across the USB somehow as it doesn't happen when you unplug the laptop. This is a fine fix for a 45 minute show or something but it gets a bit squeaky bum time when doing a long full length show! The odd thing is on rare occasions it doesn't make the noise when plugged in. It's a sound I've heard before on PC's

Can anyone, for my own education, enlighten me as to what this is actually likely to be, and if anything will fix it? I've tried DI's etc. I'm tempted to try an ART DTI as reviewed in this months SOS but I am guessing that would only solve problems introduced later in the chain? I'm pretty sure that externally powering the interface doesn't fix the problem either (though I shall try this again if anyone thinks it might fix it).

Thanks in advance for any suggestions!
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Re: What exactly IS that laptop noise, and how do I fix it?

Postby Steve A » Mon Jan 23, 2012 11:00 am

I've encountered this before as well, it's quite common. You're almost certainly experiencing a ground loop. I get around it by using a DI box with a ground lift facility (specifically a Radial JPC).
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Re: What exactly IS that laptop noise, and how do I fix it?

Postby infiniteloop » Mon Jan 23, 2012 11:32 am

The No1 reason why I ALWAYS advise to clients to use a Mac if possible for ANY live performance work. I've yet to come across this issue with a Mac but lost count of the amount of times I've had to deal with it under live conditions. It's really something PC laptop manufacturers should address immediately.
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Re: What exactly IS that laptop noise, and how do I fix it?

Postby lewk » Mon Jan 23, 2012 11:39 am

Steve A wrote:I've encountered this before as well, it's quite common. You're almost certainly experiencing a ground loop.

I'm not convinced it is, I've tried it on seperate power supplies, all sorts of theatres, different DI boxes with lifts, everything, and it never fixes it.

infiniteloop wrote:The No1 reason why I ALWAYS advise to clients to use a Mac if possible for ANY live performance work. I've yet to come across this issue with a Mac but lost count of the amount of times I've had to deal with it under live conditions. It's really something PC laptop manufacturers should address immediately.

Agreed. My personal computer is a macintosh but I'm loathe to bring it into work, and school won't shell out for a new mac laptop because of the high cost to low use ratio, plus the ICT won't allow them on the network. It's massively frustrating!
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Re: What exactly IS that laptop noise, and how do I fix it?

Postby Hugh Robjohns » Mon Jan 23, 2012 11:44 am

The usual problem is a ground loop, either via the laptop's mains power supply or the supply of the interface. Ground loops often cause hums and buzzes, but it's also quite common to find noise from the graphics cards getting in there too.

The solution is usually as simple as breaking the ground loop at the audio outputs of the sound card, and a transformer box like the ART DTI or ART CleanBox2 does that extremely well, with negligible quality loss and quite cost-effectively. But you do have to be methodical about how you break the ground loop and make sure that you are breaking all of them, not just one of several!

Martin has a comprehensive FAQ in the PC forums about solving ground loop noises and it would be well worth reading it.

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Re: What exactly IS that laptop noise, and how do I fix it?

Postby lewk » Mon Jan 23, 2012 11:50 am

Hugh Robjohns wrote:The usual problem is a ground loop, either via the laptop's mains power supply or the supply of the interface. Ground loops often cause hums and buzzes, but it's also quite common to find noise from the graphics cards getting in there too.

The solution is usually as simple as breaking the ground loop at the audio outputs of the sound card, and a transformer box like the ART DTI or ART CleanBox2 does that extremely well, with negligible quality loss and quite cost-effectively. But you do have to be methodical about how you break the ground loop and make sure that you are breaking all of them, not just one of several!

Martin has a comprehensive FAQ in the PC forums about solving ground loop noises and it would be well worth reading it.

hugh

Thanks Hugh, I'll go read it now. Much obliged! It was your review of the DTI that piqued my interest. It probably is graphics card noise, then!
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Re: What exactly IS that laptop noise, and how do I fix it?

Postby infiniteloop » Mon Jan 23, 2012 11:51 am

I think Steve is right, or at least on the right track. The very fact that when you unplug the laptop from the mains & then the noise vanishes is absolutely typical with this problem & would almost certainly indicate a mains loop. There's been many threads & solutions posted in previous forums so have a search for those & best of luck.
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Re: What exactly IS that laptop noise, and how do I fix it?

Postby Steve A » Mon Jan 23, 2012 11:58 am

I hate to be the one busting the all too often trotted out myth on this occasion but I have had experienced this problem with my MacBook Pro just as often as I have with PC laptops.
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Re: What exactly IS that laptop noise, and how do I fix it?

Postby infiniteloop » Mon Jan 23, 2012 12:01 pm

I'm more than a bit surprised to hear that.! I've used Mac lpatops for live performance for the past 12 years and have never had that problem even once. Hence why I recommend Mac laptops for any live work.
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Re: What exactly IS that laptop noise, and how do I fix it?

Postby Hugh Robjohns » Mon Jan 23, 2012 12:15 pm

I've seen/heard it with mac laptops too. iBooks etc may be wonderful things, but they can't change the laws of physics. I suspect the real reason you've never had a problem is simply because a lot (but certainly not all) of mac power supplies are ungrounded class II devices!

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Re: What exactly IS that laptop noise, and how do I fix it?

Postby Hugh Robjohns » Mon Jan 23, 2012 12:18 pm

lewk wrote:It was your review of the DTI that piqued my interest.

It definitely works when the problem really is a ground loop.... but there is another possibility worth considering and exploring, and that is of direct radiated interference from the PSU brick itself. This can be an issue if you are running unbalanced audio lines close to the PSU brick. Careful re-orientation of the PSU can help as they often radiate more strongly in some directions than others, but ideally keep audio cables well away from mains and other computer cables, and use balanced connections where possible.

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Re: What exactly IS that laptop noise, and how do I fix it?

Postby Steve A » Mon Jan 23, 2012 12:21 pm

Normally it's not a problem because I always run it through the Radial box but it caught me out a number of times last year when the ground lift switch on the DI got nudged under the case and got inadvertently swtiched off. We didn't succesfully diagnose it straight away so for a couple of gigs we had to put up with a background hum unless we disconnected the laptop PSU which is something I only feel confident doing for short gigs! Admittedly it wasn't nearly as severe as what I have heard from some latops, but it was definitely there.
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Re: What exactly IS that laptop noise, and how do I fix it?

Postby infiniteloop » Mon Jan 23, 2012 12:31 pm

Hugh Robjohns wrote:a lot (but certainly not all) of mac power supplies are ungrounded class II devices!

hugh

I guess I've just been lucky with the many Mac laptops I've had over the years. However, could this issue not be viably addressed with PC laptops avoiding the need for additional hardware to solve what is undoubtedly a very common problem.?
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Re: What exactly IS that laptop noise, and how do I fix it?

Postby Hugh Robjohns » Mon Jan 23, 2012 12:43 pm

There are lots of potential ways of fixing the problem. Having ungrounded class II mains supplies is one way, but there are some downsides to that approach. Quite a few PC lapstops have ungrounded supplies too... but it might not help much if the audio interface is grounded through its own external power supply!

Providing transformer isolated outputs on audio interfaces would be another way or always using balanced interconnections with proper grounding schemes inside the audio gear is another. But again, costs, operational flexibility and the way people end up using the equipment often make such desirable goals impractical.

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Re: What exactly IS that laptop noise, and how do I fix it?

Postby Sheriton » Mon Jan 23, 2012 2:25 pm

There are a couple of approaches I use...

1. My playout machine is in a rackmount case, inside a rack flightcase. Using a PCI-based soundcard with external breakout box with balanced connections. No power supply / graphics card / mouse noise issues ever, no matter what I connect it to or how. It's big and heavy, but then no-one will ever try to walk out the venue with it stuffed up their jumper.
2. When using a digital desk, I connect optically. No ground loop issues there.

For me, it's all about using the right tool for the job. Just because a laptop offers similar functionality, doesn't mean it's going to always do a good job.

In a school environment, you're bound to be able to procure a "retired" desktop PC you could use and dedicate it just to this one job.
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Re: What exactly IS that laptop noise, and how do I fix it?

Postby shufflebeat » Mon Jan 23, 2012 2:49 pm

I've been using the Art DTI as an isolating interface between my small PA and house systems and as a general problem solver. It does what it does very well but in my home recording setup (PC laptop, Fast Track interface) it was less effective at solving this problem than the £15 isolator from Maplins (of which I am now the proud owner of 2). This might indicate that ground loop was not the only problem and as yours is a similar setup it might be worth a punt.

It's about the diameter of a Red Bull can and has 2xRCA phonos (so unbalanced) poking out of each end. I think it was initially designed for car audio but I've often seen it recommended for this purpose.

One advantage of the DTI is it can produce balanced signals. This may or may not be important to you.
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Re: What exactly IS that laptop noise, and how do I fix it?

Postby Hugh Robjohns » Mon Jan 23, 2012 4:17 pm

shufflebeat wrote:It does what it does very well but in my home recording setup (PC laptop, Fast Track interface) it was less effective at solving this problem than the £15 isolator from Maplins


I'm amazed... and I wonder what the physical differnce between the two devices could be?

One advantage of the DTI is it can produce balanced signals. This may or may not be important to you.


The whole point of isolating transformers is that they are agnostic as far as the connection formats are concerned. A transformer doesn't care whether the source or destination are balanced or unbalanced, and can converter between either with ease assuming the right connectors are use or wired appropriately.

Picking up on a point someone made earlier, the advantage of boxes like the DTI and Cleanbox2 (and presumably your maplin adapters) is that they are designed to work with line levels in and out.

Using a DI box with a ground lift switch will break the ground loop, but they are generally designed to provide a mic-level output so you end up attenuating a line signal and then have to amplify it all over again, potentially introducing noise and distortion unnecessarily.

So while a DI box can be used in an emergency (or if you really do want a mic-level output for some valid practical reason), a proper line-level isolator is a better idea. The ART Cleanbox2 and DTI boxes I mentioned are about £35 and £40 respectively -- the DTI being more expensive because it has multiple I/O connectors in different formats. Internally they are more or less identical.

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Re: What exactly IS that laptop noise, and how do I fix it?

Postby MarkOne » Tue Jan 24, 2012 2:23 pm

Had a similar problem the other day, and so I went to my general bits and bobs box and found my Art Cleanbox 2, plugged it in and it made the buzz worse (!) Also found a cheap and nasty Behringer hum destroyer that IIRC is basically the same thing (i.e. a couple of 1:1 txrs in a box), and it gave me a nice hum free signal (can't say that it is completely transparent though!) So now I'm thinking that the cleanbox has some kind of fault... Do people think that's likely?
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Re: What exactly IS that laptop noise, and how do I fix it?

Postby Hugh Robjohns » Tue Jan 24, 2012 3:42 pm

MarkOne wrote: So now I'm thinking that the cleanbox has some kind of fault... Do people think that's likely?

When faced with faults of this kind one has to apply a logical process to find and eliminate the problem, and that requires technical understanding of all the equipment concerned, it's I/O wiring, the significance of the cable wiring connecting to and from the transformer box, and any environmental factors such as the proximity of strong magnetic radiators like mains transformers.

Fundamentally, when a buzz or other noise is due to a ground loop, breaking the ground loop with a transformer will remove the ground loop noise. But in multichannel systems there are probably multiple ground loops and they will all eed to be dealt with.

Different transformer boxes are wired differently in respect of the case and I/O connector grounds. It is very easy to effectively re-make the ground loop or even create additional loops by using inappropriate balanced/unbalanced cables or adapters, or by allowing the case to touch something that is already earthed.

Transformers are also quite susceptible to radiated magnetic fields, so while inserting a transformer isolation box might break a ground loop, if it is then placed directly over a mains transformer it is likely to capture and inject even more hum!

So yes, it is possible that your Cleanbox 2 is faulty... but there is very little in there to go wrong. It's much more likely to be an issue with the cables or connectors you were using, or where you placed the box.

The other possibility is that the ground loop wasn't where you thought it was, and installing the Cleanbox 2 actually removed the grounding from a class II source device. In this situation it is possible for that device to act like an aerial and pick up all manner of radiated interference!

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Re: What exactly IS that laptop noise, and how do I fix it?

Postby Martin Walker » Thu Feb 02, 2012 8:16 pm

Hugh Robjohns wrote:When faced with faults of this kind one has to apply a logical process to find and eliminate the problem, and that requires technical understanding of all the equipment concerned, it's I/O wiring, the significance of the cable wiring connecting to and from the transformer box, and any environmental factors such as the proximity of strong magnetic radiators like mains transformers.

Fundamentally, when a buzz or other noise is due to a ground loop, breaking the ground loop with a transformer will remove the ground loop noise. But in multichannel systems there are probably multiple ground loops and they will all eed to be dealt with.

Different transformer boxes are wired differently in respect of the case and I/O connector grounds. It is very easy to effectively re-make the ground loop or even create additional loops by using inappropriate balanced/unbalanced cables or adapters, or by allowing the case to touch something that is already earthed.

Excellent answer there from Hugh - this is why I wrote a step-by-step guide to tracking down ground loops that (hopefully) should be relatively foolproof:

www.soundonsound.com/sos/jul05/articles/qa0705_1.htm

Only when you have stripped your audio system down to the absolute basics and got a completely clean signal coming through with no background nasties is its worth starting to plug in the other gear items one by one, and dealing with each and every ground loop that you find in the process.

Otherwise you may have several different ground loops that result in changing background interference as you try different things out - even cleaning the earth pin on one mains plug might make the interference better OR worse depending on how this changes the topology of the various ground loops fighting with each other


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Re: What exactly IS that laptop noise, and how do I fix it?

Postby Scatamonky » Tue Feb 21, 2012 10:17 pm

This problem has recently reared its ugly head in my setup. But only through the monitors which run through a cheap Laney head. And only since I replaced the original Dell power supply with a cheap replacement item (not Dell) off eBay. Isn't there a device that goes on the plug end to kill the hum? I know you can run the signal from the laptop through a DI box, use the ground lift and then into the desk, but isn't that masking rather curing the hum?
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Re: What exactly IS that laptop noise, and how do I fix it?

Postby seablade » Tue Feb 21, 2012 11:30 pm

Scatamonky wrote:This problem has recently reared its ugly head in my setup. But only through the monitors which run through a cheap Laney head. And only since I replaced the original Dell power supply with a cheap replacement item (not Dell) off eBay. Isn't there a device that goes on the plug end to kill the hum? I know you can run the signal from the laptop through a DI box, use the ground lift and then into the desk, but isn't that masking rather curing the hum?

No that is curing the hum. And lifting the AC ground is a BAD IDEA on any piece of equipment. Isolating the audio ground is both safer and the correct way to solve this if it is indeed a ground loop.

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Re: What exactly IS that laptop noise, and how do I fix it?

Postby Scatamonky » Wed Feb 22, 2012 12:11 am

Thanks Seablade - as always, clear and concise answers. I have a spare DI box with a ground lift. I will try that next gig and see how I get on. Although...ATM I take a mini jack to phono and put it from laptop to the stereo input on my desk (Allen & Heath ZED 22 FX), if I get a mini stereo jack to 2 mono 1/4 jacks...into the DI box, then 2 XLR mic leads out and into 2 desk channels....is that the only way to do it? I've only got one spare channel ! LOL
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Re: What exactly IS that laptop noise, and how do I fix it?

Postby Hugh Robjohns » Wed Feb 22, 2012 11:49 am

You need the ART DTI box. I reviewed it here:

http://www.soundonsound.com/sos/feb12/a ... rt-dti.htm

It is a pair of line transformers in a box, with almost every connector known to man on both input and output.

So you would connect your minijack to phono lead to the input of the box, and then if you need to use the stereo phono input sockets on your desk, use a stereeo phono-phono lead on the output of the DTI to the desk input.

The transformers in the box don't care whether they're connected to balanced or unbalanced sources or destinations, but they do break the ground loop.

This solution is far more practical than using normal instrument DI boxes because it's all in one box, has convenient connectors for your application, and the transformers are optimised for line level signals. In contrast the output of a DI boxes is optimised for mic level signals, and the transformers can saturate badnly if you try to send line levels out!

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Re: What exactly IS that laptop noise, and how do I fix it?

Postby chris... » Wed Feb 22, 2012 12:23 pm

Hugh Robjohns wrote:I've seen/heard it with mac laptops too. iBooks etc may be wonderful things, but they can't change the laws of physics. I suspect the real reason you've never had a problem is simply because a lot (but certainly not all) of mac power supplies are ungrounded class II devices!
The MacBook Pro power supply with which I'm familiar is class II (double-insulated). However, whether or not it's grounded depends on whether you use:

(A) the stubby mains plug thing that clips onto the PSU brick - nice and tidy

or:

(B) the longer mains lead that plugs into the brick - letting you work further from the socket

Despite being class II, the PSU brick itself has an earth connection. With (A), this is connected to earth on the mains plug. But with (B), it isn't. Go figure!

So if you're using (B), try (A) - or vice versa.

Disclaimer - for all I know, this may have changed since I bought my last MBP.
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Re: What exactly IS that laptop noise, and how do I fix it?

Postby Guy Johnson » Wed Feb 22, 2012 8:02 pm

Mac lappy owner here, I've had noise happen 5 or 6 times in a few years, only with one power-supply, and it stopped after I put a couple of turns of the output wire through a ferrite suppressor. No more problem, which rather surprised me ... but then it only occasionally did it, anyway.

Owning an ART DTI box is a good idea anyway — a very useful tool. Using a similar device with nice transformers in it a few years ago improved the sound of a Studiomaster live mixer that had otherwise unbalanced outputs.
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Re: What exactly IS that laptop noise, and how do I fix it?

Postby chris... » Wed Feb 22, 2012 10:31 pm

chris... wrote:(A) the stubby mains plug thing that clips onto the PSU brick - nice and tidy

or:

(B) the longer mains lead that plugs into the brick - letting you work further from the socket

Despite being class II, the PSU brick itself has an earth connection. With (A), this is connected to earth on the mains plug. But with (B), it isn't. Go figure!
Arghh - just reread that and realised I got it backwards!

The longer lead is grounded, but the stubby plug isn't.

(both made by Apple and come with the laptop)

Sorry for confusion.
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Re: What exactly IS that laptop noise, and how do I fix it?

Postby Chaconne » Thu Feb 23, 2012 3:16 am

Somebody asked the same question in the tech Q+A in this months DJ Mag.

The reply mentions power supplies, and filters. Having quickly googled this I found this guy demonstrating a filter on youtube...

ground loop noise filter


More research finds these on ebay for only £5 odd.

Is there any reason these might not do the trick?
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Re: What exactly IS that laptop noise, and how do I fix it?

Postby Mike Stranks » Thu Feb 23, 2012 10:24 am

Chaconne wrote:Somebody asked the same question in the tech Q+A in this months DJ Mag.

The reply mentions power supplies, and filters. Having quickly googled this I found this guy demonstrating a filter on youtube...

ground loop noise filter


More research finds these on ebay for only £5 odd.

Is there any reason these might not do the trick?
Sure, they'll work, but a couple of things to take into account...

1) If we're talking audio in the studio (home or otherwise) or on-stage then anything that goes into the signal-chain needs to be as audio-transparent as possible. With these ground-loop isolators (not technically filters) the quality of the transformers is paramount. £5 is £5... and I'd suspect that these might easily get saturated if over-driven.

2) On the road I'd be wary of the flimsy cable and plastic phonos on this unit. I much prefer something that I can plug more heavy-duty cables into which has it's own substantial sockets. I'd settle for jacks, but would prefer XLRs.

... and having been banging the drum for Orchid Electronics recently (with whom I have no connection), they also do some attractively-priced ground-loop isolators.
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Re: What exactly IS that laptop noise, and how do I fix it?

Postby Hugh Robjohns » Thu Feb 23, 2012 10:32 am

Yes, that car hifi line isolator will work. It is doing exactly the same job as the line transformer boxes I mentioned above.

However, it lacks the flexibility of connectors (which might not be important to some users), is wired for unbalanced connection throughout (which might not be important to some users), and might not be magnetically shielded (which might not be important to some users).

I don't know if the magnetic shielding is absent or not... but looking at the item in question I wouldn't be surprised. In it's intended application in a car, magnetic shielding isn't likely to be an issue at all and so it could be that the manufacturer has left this out to save money, but in an environment with mains transformers all over the place it could be very significant, and result in the isolator breaking a ground loop but injecting mains ghum itself!

Finally, you do tend to get what you pay for. Cheap transformers generate quite a lot of distortion, particularly at low frequencies, and saturate at relatively low levels (worse at LF again).

I've measured the ART DTI and Cleanbox II products and they perform surprisingly well for the money. I also have a Canford line isolator that uses Lundahl transformers and which costs a lot more than the ART designs, but the technical performance is significantly better. In most situations I'm quite happy to use the ART boxes, but where quality really is important, or I'm working with high level signals or those with high level LF, then I reach for the Canford unit.

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