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The laptop AC hum noise issue again!

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The laptop AC hum noise issue again!

Postby TrickyDicky » Thu Jan 19, 2012 2:11 pm

My laptop PC is connected to my Mac and all is well apart from one tiny thing..

The dreaded laptop noise/earth issue!

I get this constant low lying buzz just as I go into audio record on my PC laptop and have managed to figure out after much cable swapping that its down to the AC power..

I have tried plugging the laptop seperatly into another plug, different room on an extension, and lastly pulling it out altogether and using it off its old knackered battery. On battery its a noise floor in Record mode of about -84.0 which i think is ok..

So I could keep pulling out the power and use battery for whenever I want to record but the battery is knackered, so is there a simple solution to this? I have tried various noise/ground loop boxes and no luck.

Can you get a specific laptop power "brick" that would eliminate this?
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Re: The laptop AC hum noise issue again!

Postby Exalted Wombat » Thu Jan 19, 2012 2:25 pm

This
http://www.maplin.co.uk/ground-loop-isolator-33172
is what I put in my laptop bag when I anticipate having to plug into a PA system. It probably isn't terribly hi-fi, but it works.

The advantage is that it doesn't try to be clever, it just provides complete electrical isolation. And it's cheap!
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Re: The laptop AC hum noise issue again!

Postby TrickyDicky » Thu Jan 19, 2012 2:45 pm

Thanks but I tried that one, and another sturdier one and it was no use?

I didn't know whether there was a plug/adaptor that i could change ?
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Re: The laptop AC hum noise issue again!

Postby Hugh Robjohns » Thu Jan 19, 2012 3:11 pm

TrickyDicky wrote:My laptop PC is connected to my Mac

The fundamental information we need to be able to help is to know how the two machines are connected.

...have managed to figure out after much cable swapping that its down to the AC power..

It's very unlikely to be because of the AC power itself. However, it could be due to a ground loop running via the AC mains safety earth connection.

I have tried plugging the laptop seperatly into another plug, different room on an extension...

The aim with ground loops is to break the loop altogether, but in a safe manner. Extending the loop size by using alternatice mains sockets or extaneion cables usually makes the problem worse, not better. The smallest loop size is obtained when the relevant devices are plugged into adjacent sockets... but even that doesn't always cure the problem.

noise floor in Record mode of about -84.0 which i think is ok.

I presume you're using some form of analogue connection. A noise floor at -84dBFS is quite acceptable for most purposes, and far better than could be achieved easily with analogue tape, but it falls below the -110dBFS that should be possible with high quality analogue electronics and converters.

I have tried various noise/ground loop boxes and no luck.

If the noise problems is genuinely caused by one or more ground loops, then breaking those loops is the only solution. Tranformer isolators for analogue and digital audio connections always work if applied correctly. hence the need to know precisely how you have connected the PC and Mac.

Another possibility instead of a ground loop issue is that the laptop power supply might be radiating EM or RF interference which is getting in to the analogue audio connections.

Can you get a specific laptop power "brick" that would eliminate this?

A 'double insulated' or Class II power supply which is designed not to require a mains safety earth would avoid any possibility of a ground loop, and these are sometimes available for specific laptops.

There are 'mains ground eliminator' (or 3 to 2-pin) main plug adapters available in some countries, but these are intrinsically UNSAFE. Removing the safety earth connection from a Class 1 supply which is designed to use one would be unsafe and is definitely not recommended.

If the problem is caused by some form of interference radiating from your existing laptop supply, moving it as far away as possible from any analogue audio connections should help, as will experimenting with it's relative orientation since these things tend to radiate more strongly in some directions than others.

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Re: The laptop AC hum noise issue again!

Postby Exalted Wombat » Thu Jan 19, 2012 3:12 pm

TrickyDicky wrote:Thanks but I tried that one, and another sturdier one and it was no use?

I didn't know whether there was a plug/adaptor that i could change ?

If you can find an alternative adapter that delivers EXACTLY the required voltage at sufficeient amps it's worth giving it a try.

When you're trouble-shooting this, set up with minimum items connected. Just the laptop, the receiving computer and a pair of headphones. Everything else unplugged.
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Re: The laptop AC hum noise issue again!

Postby Martin Walker » Thu Jan 19, 2012 9:02 pm

All good advice there, and as Hugh mentions a DI box should cure any such problem, but you do have to be very systematic when tracking down an earth loop to know exactly where to place it in your setup.

Have a read of this Q &A I wrote for SOS July 2005 for a step-by-step guide to tracking down the cause:

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

Hope it helps!


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Re: The laptop AC hum noise issue again!

Postby TrickyDicky » Sun Jan 22, 2012 1:05 pm

Thanks for these tips, but i'm pretty sure its the AC adaptor power supply..

I have tried to track down the hum, and yes the Mac is going out of the headphone and split into my PC Windows XP USB interface L&R (so very simple)

The laptop noise/hum vanishes when I pull the power on the PC laptop (the laptop that's recording) and its running off its slow and short battery!

So surely this must be the problem? :crazy: :?
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Re: The laptop AC hum noise issue again!

Postby Martin Walker » Sun Jan 22, 2012 2:25 pm

The PSU is not the problem, but the CAUSE of the problem.

The noises happen when you plug in your AC power supply because this completes the ground loop - this is the usual culprit, and the only safe way to resolve the problems is:

a) Unplug the AC power supply and run of batteries

b) Replace the AC power supply with another model that is double insulated and with no connection to mains earth.

c) Breaking the ground loop in the audio chain using a line-level DI box, most often between the output of the audio interface and whatever it’s plugged into.


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Re: The laptop AC hum noise issue again!

Postby Exalted Wombat » Sun Jan 22, 2012 2:40 pm

TrickyDicky wrote:Thanks for these tips, but i'm pretty sure its the AC adaptor power supply..

I have tried to track down the hum, and yes the Mac is going out of the headphone and split into my PC Windows XP USB interface L&R (so very simple)

The laptop noise/hum vanishes when I pull the power on the PC laptop (the laptop that's recording) and its running off its slow and short battery!

So surely this must be the problem? :crazy: :?

Remind us - do you get the buzz when ONLY headphones are attached directly to the PC? If so, you can blame the psu, or its associated circuitry inside the laptop. This may be insoluble. Some computers, particularly laptops, are just not designed to be capable of quality audio from their internal systems.

What are you actually using the laptop for when you have this setup?
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Re: The laptop AC hum noise issue again!

Postby TrickyDicky » Sun Jan 22, 2012 3:00 pm

Exalted Wombat wrote:
TrickyDicky wrote:Thanks for these tips, but i'm pretty sure its the AC adaptor power supply..

I have tried to track down the hum, and yes the Mac is going out of the headphone and split into my PC Windows XP USB interface L&R (so very simple)

The laptop noise/hum vanishes when I pull the power on the PC laptop (the laptop that's recording) and its running off its slow and short battery!

So surely this must be the problem? :crazy: :?

Remind us - do you get the buzz when ONLY headphones are attached directly to the PC? If so, you can blame the psu, or its associated circuitry inside the laptop. This may be insoluble. Some computers, particularly laptops, are just not designed to be capable of quality audio from their internal systems.

What are you actually using the laptop for when you have this setup?

I'm using my PC laptop with Reaper 4, as an Audio Recorder from my Mac/VST's so I can play anything live straight into the PC and it record and I compile it all on a seperate system (PC Laptop), and hence I'm using a simple splitter lead from Macbook headphones out > PC Laptop USB audio interface analog in (L&R) so its really straight forward..

It must have worked ok at some point as I recorded a National TV ad score like this! (but then again that was at a different location) which may have had different power supply etc.

The Macbook has a seperate 2nd Monitor plugged into it, which some posts around the internet suggest that this can cause noise from the Macbook output when a 2nd monitor is attached. But when this is all set up, and I 'pull' the 2nd monitor to cure it, the noise is still there so I don't believe its that?

:headbang:
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Re: The laptop AC hum noise issue again!

Postby TrickyDicky » Fri Jan 27, 2012 1:02 pm

Any thoughts or advice anyone?

:crazy:
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Re: The laptop AC hum noise issue again!

Postby Hugh Robjohns » Fri Jan 27, 2012 1:34 pm

You've had all the advice there is to give.

Pick any one of the three options that Martin has listed.

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Re: The laptop AC hum noise issue again!

Postby TrickyDicky » Mon Jan 30, 2012 12:46 pm

Martin Walker wrote:The PSU is not the problem, but the CAUSE of the problem.

The noises happen when you plug in your AC power supply because this completes the ground loop - this is the usual culprit, and the only safe way to resolve the problems is:

a) Unplug the AC power supply and run of batteries

b) Replace the AC power supply with another model that is double insulated and with no connection to mains earth.

c) Breaking the ground loop in the audio chain using a line-level DI box, most often between the output of the audio interface and whatever it’s plugged into.


Martin


Thanks Martin, but now I'm really confused..

a) I unplugged the AC to run off batteries, and today the hum/noise loop was still there? If it helps I'm running a Compaq Laptop on its base unit, which it sits into, and the AC plugs into the base unit to give the laptop power, plus give me extra connections for USB, mouse keyboard that run off the base unit etc.

b) I'm not too sure where to find another Compaq AC unit that is double insulated? Would there be some on eBay? (have tried but nothing came up?)

c) The ground loop isolator, would this go from :

Mac > Headphone out 3.5mm cable to phono stereo split > ground loop isolator > Audio interface stereo input ?

You mention "most often between the output of the audio interface and whatever it’s plugged into", the output of my audio interface goes straight to my powered monitors? :?

Sorry for all the confusion, but tracking down this little ba***rd is really getting to me! :roll:
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Re: The laptop AC hum noise issue again!

Postby ef37a » Mon Jan 30, 2012 3:16 pm

Get the Maplin isolator E.W.mentions and insert it in the line twixt AI and monitors. If that fixes the hum, result. If you can discern audible degradation maybe look at the Art DTI that Hugh thought highly of in the Feb issue for a nifty.

More expensive (but you could bounce it back) is the usb isolator from www.cesys.com 84ees but would give a general rather than specific (to the audio feed) solution...IF it works!

Face it friend, this is going to cost you SOME money!

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Re: The laptop AC hum noise issue again!

Postby TrickyDicky » Mon Jan 30, 2012 3:31 pm

Thank you Dave for your suggestion...

But I believe its not worth it for a PC laptop this old.. I have diagnosed pops clicks after all the tweaks in Windows, and now this Earth hum which I have tried to chase down the line, to see where its coming from!

Also i can't really put it between AI and Speakers as they are 1/4" jacks and the Isoloator is phono, so I'd have to swap cables and adaptors!

No this just isn't worth it, I'm going over to the Mac fully now I think, and can use Parallels in OS X for any Windows programs, and it works perfectly..

I don't want to start a war, but the PC is so draining, how do you lot get anything done? :D
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Re: The laptop AC hum noise issue again!

Postby Hugh Robjohns » Mon Jan 30, 2012 5:44 pm

By using sensible tools in a sensible way with sensible wiring strategies!

The problems you are having are nothing to do with the fact that one of your computers is a PC, and everything to do with unbalanced audio connections and multiple grounding paths.

I'm glad you arrived at an acceptable solution, but I suspect, though, that should you change your mac laptop for a desktop machine your hum troubles will return with a vengence!

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Re: The laptop AC hum noise issue again!

Postby Exalted Wombat » Mon Jan 30, 2012 5:53 pm

TrickyDicky wrote:Also i can't really put it between AI and Speakers as they are 1/4" jacks and the Isoloator is phono, so I'd have to swap cables and adaptors!

Hardly a deal-breaker, surely?
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Re: The laptop AC hum noise issue again!

Postby Martin Walker » Mon Jan 30, 2012 5:57 pm

And just to put a gentle close to this thread, let me once again provide a link to my step-by-step guide to tracking down the cause of any ground loop:

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

If you’re not systematic then it’s unlikely you’ll solve the problem :headbang:


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Re: The laptop AC hum noise issue again!

Postby TrickyDicky » Mon Jan 30, 2012 5:58 pm

I've spent too much time and money I think now on reviving this laptop (as I'm primarily a Mac user) to see what Windows had to offer, but after doing a couple of reformats, the windows tweaks, and now this earth hum, plus driver issues, I think I'm back off to the land of Mac.. :bouncy:
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Re: The laptop AC hum noise issue again!

Postby TrickyDicky » Thu Feb 02, 2012 8:02 am

Just to add to this thread, I realised that the noise went down from an annoying noticeable -50/-60db into the PC, to an Ok -80db (which I believe is ok as a noise floor?) even though after numerous tracks building up, can obviously increase the noise..

Anyway this dropped once I unplugged a USB printer on the Mac side! (The Mac is outputting sound and recording into the PC laptop)

Secondly as a thought (not sure if I'm going down this route still) would a 3.5mm stereo jack out to split L & R XLR plugs be a better or quieter option (grounded cable?) as the input of my Interface takes either jack or XLR, and XLR maybe a better option? :headbang:
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Re: The laptop AC hum noise issue again!

Postby Exalted Wombat » Thu Feb 02, 2012 10:19 am

TrickyDicky wrote:Just to add to this thread, I realised that the noise went down from an annoying noticeable -50/-60db into the PC, to an Ok -80db (which I believe is ok as a noise floor?) even though after numerous tracks building up, can obviously increase the noise..

Anyway this dropped once I unplugged a USB printer on the Mac side! (The Mac is outputting sound and recording into the PC laptop)

Secondly as a thought (not sure if I'm going down this route still) would a 3.5mm stereo jack out to split L & R XLR plugs be a better or quieter option (grounded cable?) as the input of my Interface takes either jack or XLR, and XLR maybe a better option? :headbang:

So you can blame it on the Mac now :-)
You haven't really been listening to our advice at all, have you?

Have you told us what interface you own? If it has both jack and XLR inputs it's likely that the jacks are designed to accept a line level signal, the XLRs are for microphones.
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Re: The laptop AC hum noise issue again!

Postby Martin Walker » Thu Feb 02, 2012 8:35 pm

Exalted Wombat wrote:You haven't really been listening to our advice at all, have you?

Obviously not :headbang:

TD - You still seem to be plugging and unplugging things at random, and ground loops demand a step-by-step approach (as we've said again and again)

Start with the simplest setup, make sure it works with no background noises, then plug the next gear item in - if it remains silent then plug in another until you hear the first ground loop noises and then you know which is the culprit and where to tackle the problem.


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Re: The laptop AC hum noise issue again!

Postby Hugh Robjohns » Fri Feb 03, 2012 10:34 am

And rather than use the minijack headphone output to source the audio feed for the PC, get a decent interface on the Mac, and then run balanced line level signals between the two.

Balanced signals are ground-free by definition and if a ground loop exists through the cable screens you can break the screen easily without affecting the audio in any way. Much easier.

...But as others have pointed out, your system has multiple ground loops that ned to be identified and resolved first.

As for the noise floor, -80dBFS might be adequate for many kinds of music, but as a general system noise floor it's pretty poor. Even budget interfaces will manage well in excess of -100dBFS these days. I suspect your high system noise floor is due to the use of the headphone output...

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