You are here

Troubleshooting Noise/Interference

All about the tools and techniques involved in capturing sound, in the studio or on location.

Troubleshooting Noise/Interference

Postby ste-c » Sun Dec 01, 2019 7:18 pm

Hi!

I've noticed a weird noise when I'm recording bass direct into my interface.

I was wondering if anyone could offer opinions as to where this issue might be. It seems to be happening with both of my basses and both instrument cables. Could there be interference from something else? Or do you think the interface itself is the problem?

Signal path is literally BASS > CABLE > INTERFACE > USB CABLE > LAPTOP (Logic X). The interface is an old M Audio Mobile Pre II.

Here is an example.

https://soundcloud.com/clearyscorner/tr ... 19/s-3FIji

Thanks!
ste-c
Posts: 3
Joined: Sun Dec 01, 2019 7:16 pm

Re: Troubleshooting Noise/Interference

Postby Hugh Robjohns » Sun Dec 01, 2019 8:08 pm

I'm not in a place where I can audition your track, but I'd hazard a guess that your problem is due to your whole recording system lacking a proper earth reference.

The laptop has no mains safety earth (even if mains powered*), the interface is bus-powered, so no earth there, either, and obviously there's no earth in the bass...

As a result, the guitar cable screen and the cases of the interface and laptop all act as aerials to pickup whatever interference is in the aether, rather than acting as the intended earthed screen to keep it all out.

So... The probable solution is to provide a proper earth to the system. There are several ways of doing that, depending on circumstances. *Some Mac laptop mains PSUs do pass the mains safety earth through (but most don't...) So you could look for a grounded mains PSU for the laptop.

Alternatively, you could connect one of the interface's inputs or outputs to something that has a mains safety earth -- such as a powered monitor speaker, for example (again, most are class-1 and grounded, but not all, so check!).

Or you can contrive some other convenient way to attach a mains safety earth to the interface in some way, such as by employing something like this: https://www.soundonsound.com/reviews/groundology-earth-connection-plug

Hope that helps.

H
User avatar
Hugh Robjohns
Moderator
Posts: 25032
Joined: Fri Jul 25, 2003 12:00 am
Location: Worcestershire, UK
Technical Editor, Sound On Sound

Re: Troubleshooting Noise/Interference

Postby Wonks » Sun Dec 01, 2019 8:25 pm

I can't hear any noise at all, which means that it must be pretty high pitched, at least over 9kHz. Or very very low.

I'd suggest recording the noise without any bass playing, then do a frequency spectrum analysis of the recorded noise to see what the main frequencies of the noise is/are.
User avatar
Wonks
Jedi Poster
Posts: 10140
Joined: Thu May 29, 2003 12:00 am
Location: Reading, UK
Correcting mistakes on the internet since 1853

Re: Troubleshooting Noise/Interference

Postby ste-c » Sun Dec 01, 2019 8:56 pm

Thanks so much for the replies guys.

Hugh Robjohns - that's very interesting. I looked into it and my macbook does appear to be grounded via the mag safe. I tried a couple different outlets and will also check in a different room just in case. Can continue to look into this if the below details don't change anything.

Wonks - You're right it's pretty high pitched but still very audible in my setup.

The noise mostly happens when playing. So I did like you said and recorded without the playing. It seems there is something picking up some ambient noise in the room. As in you can faintly hear it if I clap or make noises in the room. Does this mean something is microphonic? Or is this normal?

Thanks again.
ste-c
Posts: 3
Joined: Sun Dec 01, 2019 7:16 pm

Re: Troubleshooting Noise/Interference

Postby Martin Walker » Sun Dec 01, 2019 9:11 pm

Just had a couple of listens and like Wonks I couldn't at first hear the problem, but then it emerged from the gloom - seems to be a low-level 'fizzy' background in time with the bass guitar notes (like a fuzz box at very low level in parallel with the clean sound).

However, if my ears aren't deceiving me it temporarily stops completely around four seconds into that 12-second clip, so it might be something to do with what you're touching on the bass guitar.

Weird one though.


Martin
User avatar
Martin Walker
Moderator
Posts: 14602
Joined: Wed Jan 13, 2010 9:44 am
Location: Cornwall, UK

Re: Troubleshooting Noise/Interference

Postby Wonks » Mon Dec 02, 2019 11:38 am

I can now hear something using headphones up loud. It sounds a lot like mechanical buzzing to me, certainly on the first few notes. It's worth checking that you haven't got anything loose on the bass that can buzz and the noise get back to the pickup via the strings.

Fender-style bridges (and any others with a height-adjustment screw on each end of the saddle) need to be set flat with respect to the baseplate, and both screws set so they are touching the baseplate. If the saddle is at an angle, then you can get one screw that's just off the baseplate and it can just touch and buzz when the string is plucked.

Alternatively if you have the basses set for low actions, you could have a slight fret buzz on some frets. Or the string break angle over the saddle isn't quite great enough and you're getting some buzz as a result.

It never harms to do that sort of simple checking.
User avatar
Wonks
Jedi Poster
Posts: 10140
Joined: Thu May 29, 2003 12:00 am
Location: Reading, UK
Correcting mistakes on the internet since 1853

Re: Troubleshooting Noise/Interference

Postby Tim Gillett » Mon Dec 02, 2019 12:32 pm

Weird sound. Almost a furry sound but then it seems to change frequency even on reasonably steady bass notes. Worth looking at it on the analyser.

Yes the bass notes just seem to be a trigger for an electronic problem. High frequency fizzes which go both up and down in frequency.
Tim Gillett
Frequent Poster
Posts: 1888
Joined: Wed Jan 30, 2013 1:00 am
Location: Perth, Western Australia

Re: Troubleshooting Noise/Interference

Postby Martin Walker » Tue Dec 03, 2019 11:13 pm

Tim Gillett wrote:Weird sound. Almost a furry sound but then it seems to change frequency even on reasonably steady bass notes. Worth looking at it on the analyser.

Yes the bass notes just seem to be a trigger for an electronic problem. High frequency fizzes which go both up and down in frequency.

Particularly on the last note it almost sounded to me like an old-fashioned Schmitt trigger fuzz box that drops out when the input level gets too low.


Martin
User avatar
Martin Walker
Moderator
Posts: 14602
Joined: Wed Jan 13, 2010 9:44 am
Location: Cornwall, UK

Re: Troubleshooting Noise/Interference

Postby blinddrew » Tue Dec 03, 2019 11:30 pm

There's almost a sort of phasey sound to it. A sort of zwee-zwee-zwee sound.
I think you've got something picking up some RF interference.
User avatar
blinddrew
Jedi Poster
Posts: 8496
Joined: Sun Jul 05, 2015 12:00 am
Location: York
Ignore the post count, I have no idea what I'm doing...

Re: Troubleshooting Noise/Interference

Postby Hugh Robjohns » Wed Dec 04, 2019 12:56 am

ste-c wrote:I looked into it and my macbook does appear to be grounded via the mag safe.

I'm not so sure... And it really depends on the specific power supply you are using. Some connect the DC ground to the mains safety earth, but most don't.

Ideally, you could check for ground continuity with a digital multimeter, but if you dont have a suitable,device, there's a simple practical test you can do but you will need an assistant and a spare instrument cable.

Ask your assistant to take the spare instrument lead, and hold the tip of one plug against something known to be earthed: one of the screws of a mains wall socket, for example. Then place the tip,of the other plug against something that is supposed to be earthed on the interface -- the sleeve contact of the headphone socket, for example. While,your assistant is doing this, record the bass, and then see if the unwanted noises disappear when the grounding lead is being used.

H
User avatar
Hugh Robjohns
Moderator
Posts: 25032
Joined: Fri Jul 25, 2003 12:00 am
Location: Worcestershire, UK
Technical Editor, Sound On Sound

Re: Troubleshooting Noise/Interference

Postby ste-c » Mon Dec 09, 2019 2:40 am

Thanks for the all the help folks.

Hugh, I don't have a multimeter or know what would be grounded, there are no screws on my sockets. I feel so silly haha. I did connect up my preamp, which is powered by 3-prong mains, and then connected an instrument cable between the preamp and and interface. Does this count as grounding?

Anyways the sound persisted with the preamp and if I recorded through the preamp.

The noise seems to be absent when I record vocals using a microphone through this preamp into the interface. So that points to something instrument related I guess?

Anyway, I think we have ruled out a lot of things and I'm going to look into getting a new interface, which is probably overdue anyway.
ste-c
Posts: 3
Joined: Sun Dec 01, 2019 7:16 pm

Re: Troubleshooting Noise/Interference

Postby CS70 » Mon Dec 09, 2019 2:27 pm

Just to make sure.. you’re recording bass.. it’s not that you’re staying near the computer (especially the computer screen) when doing so, right?

When I record demos I need to step back at least a couple meters from the 27” monitors to avoid interference. Just in case of course.
User avatar
CS70
Jedi Poster
Posts: 4486
Joined: Mon Nov 26, 2012 1:00 am
Location: Oslo, Norway
Silver Spoon - Check out our latest video  and the FB page

Re: Troubleshooting Noise/Interference

Postby cyrano.mac » Tue Dec 10, 2019 6:24 pm

Hugh Robjohns wrote:The probable solution is to provide a proper earth to the system. There are several ways of doing that, depending on circumstances. *Some Mac laptop mains PSUs do pass the mains safety earth through (but most don't...) So you could look for a grounded mains PSU for the laptop.

All Macbook PSU's that I've ever seen, pass ground through an RC chain, as it should be. High enough impedance to get a slight tingling if ground is absent, low enough to sink most RFI and static voltage in the ground. PC laptop PSU's usually have a two prong connector. That's one reason they might be a little worse on RFI rejection.

It's also the reason Apple supplies a two-prong and a 3-prong duckhead connector.

Alternatively, you could connect one of the interface's inputs or outputs to something that has a mains safety earth -- such as a powered monitor speaker, for example (again, most are class-1 and grounded, but not all, so check!).

Or you can contrive some other convenient way to attach a mains safety earth to the interface in some way, such as by employing something like this: https://www.soundonsound.com/reviews/groundology-earth-connection-plug

Hope that helps.

H

That's a potentially life-threatening device. Imagine what would happen if the mains ground is bad and another device fails, shortening live mains to the ground connection...

It would put live mains on all the metal parts of the audio circuit. Like on the housing of the jack plug you use for your guitar.

I sure hope there's a ground breaker on the circuit in that case. If not, you're dead.
cyrano.mac
Regular
Posts: 88
Joined: Sun Jun 02, 2019 5:00 pm

Re: Troubleshooting Noise/Interference

Postby Hugh Robjohns » Tue Dec 10, 2019 6:47 pm

cyrano.mac wrote:That's a potentially life-threatening device. Imagine what would happen if the mains ground is bad and another device fails, shortening live mains to the ground connection...

Mains safety is paramount, of course, but all the grounding plug is doing is providing the same path to the mains safety earth that exists normally and safely when any Class 1 device is connected to the Class 2 device.

Added to which your doom-mongering requires several simultaneous failures and the complete absence of any safety devices (fuses, MCB, RCD) in the mains feed... which should never be the case.

H
User avatar
Hugh Robjohns
Moderator
Posts: 25032
Joined: Fri Jul 25, 2003 12:00 am
Location: Worcestershire, UK
Technical Editor, Sound On Sound

Re: Troubleshooting Noise/Interference

Postby cyrano.mac » Tue Dec 10, 2019 7:19 pm

I've seen that exact scenario in practice. A dear friend died.

It's not unusual to have a bad ground. All it takes is dry weather and a sandy soil. Or a sloppy electrician. And one isolation failure.

I don't know what's inside these "magical" ground plugs. I hope there's an RC circuit to prevent the worst. Is there any approval for that stuff?

My friend was rigging some lights during a festival. Of course, mains wasn't connected yet. But someone needed a bit of power, so they pulled a long wire from the cellar of a nearby pub. Unfortunately, it was the one receptacle that was connected directly to mains, next to the fuse box. It's purpose was to provide light for the electrician when the fuse box shut off. Somehow, the thing that was powered by this one connection had bad insulation.

His feet weren't even on the ground as he was up there, adjusting lights. And the scaffolding he was in was safe. We still miss him.

You should never, ever, connect audio ground to mains ground. Period.

People still die every year cause some bozo decides he's smart enough to wire the plug. I see those kinds of errors at least once a week when trouble shooting.
cyrano.mac
Regular
Posts: 88
Joined: Sun Jun 02, 2019 5:00 pm

Re: Troubleshooting Noise/Interference

Postby Hugh Robjohns » Tue Dec 10, 2019 7:37 pm

cyrano.mac wrote:I've seen that exact scenario in practice.

With respect, that lethal scenario, and the grounding option I suggested, are very different indeed and completely unrelated.

It's not unusual to have a bad ground.

Obviously, a high ground impedance can occur, but the likelihood depends on where you live (ie. the local electrical safety regulations) and the type of mains supply configuration coming into the building. Its extremely unusual to have a 'bad ground' in the UK, for example. YMMV.

I don't know what's inside these "magical" ground plugs. I hope there's an RC circuit to prevent the worst.

There's nothing magical. It's a piece of wire. An RC circuit would defeat its object. It's not a ground-lift, it's a ground-tie, replicating the hard-ground connection provided in a class-1 device.

Unfortunately, it was the one receptacle that was connected directly to mains, next to the fuse box.

That wouldn't be legal in the UK, and I'm rather surprised it's allowed where you are. :o

It's purpose was to provide light for the electrician when the fuse box shut off.

Have they never heard of torches? :headbang:

Somehow, the thing that was powered by this one connection had bad insulation.

Oh dear... substandard routine maintenance? Any needless loss of life is tragic, and I'm very sorry for your loss. But this story involves multiple catastrophic failures combined with stupidity -- albeit none the fault of your late friend. It's an inherent fact of life that it's always impossible to protect against multiple simultaneous failures of critical parts of the system. That's why we try to engineer systems so that they fail-safe with a single failure.

You should never, ever, connect audio ground to mains ground. Period.

Sorry. That's complete nonsense. There are good scientific reasons why the audio reference ground ~should~ be tied to the mains safety ground in most mains powered systems, and thats been the practical implementation in every professional studio installation I've ever been involved with.

However, multiple connections between the audio reference hround and the mains safety earth can cause problems in some systems, obviously (ground loops), just as an absence of hard grounding can cause problems in others -- especially in systems with unbalanced connections. Having said all that, a connection to mains ground is not always an essential if the system is designed properly -- as in battery powered equipment, for example, or in vehicles, or planes...

People still die every year cause some bozo decides he's smart enough to wire the plug. I see those kinds of errors at least once a week when trouble shooting.

Sad but true... the only cure is education...
User avatar
Hugh Robjohns
Moderator
Posts: 25032
Joined: Fri Jul 25, 2003 12:00 am
Location: Worcestershire, UK
Technical Editor, Sound On Sound

Re: Troubleshooting Noise/Interference

Postby cyrano.mac » Wed Dec 11, 2019 3:52 am

Sorry, Hugh, it's not extremely unlikely to have a bad ground. Wherever you are. Take old buildings, for instance. I've seen quite a few of those in the UK, with real bad electricity setups. But even if it was rare, it would be very sad to just accept the few casualties.

Electrocution is the fifth leading cause of occupational injury death in the United States:
https://injuryprevention.bmj.com/content/8/4/306

Unfortunately, the UK doesn't even bother to keep stats about electrocution. The numbers in the EU report are extrapolated from other countries' data. Go figure!

The ETCI reported 2,5 million electrocutions per year in the UK of which 200.000 needed to be hospitalised. I never saw any number on deaths, unfortunately. Again, extrapolated data, based on sampling.

Our local regulations are among the most severe, but don't protect from sheer stupidity. About half of a dozen yearly deaths could have been avoided because they were caused by safety equipment not working because of hacks like this.

Failing insulation is very rare, but it is the number one problem proper grounding should protect against.

By bridging audio and mains ground you are creating the environment in which these kind of accidents occur. You are exposing double insulated equipment to grounded equipment through the shield connection, potentially bypassing other safety measures like RC connected ground schemes. You're also potentially making the GFCI useless.
cyrano.mac
Regular
Posts: 88
Joined: Sun Jun 02, 2019 5:00 pm

Re: Troubleshooting Noise/Interference

Postby blinddrew » Wed Dec 11, 2019 9:46 am

The detail is available. Start with hse.gov.uk.
4 industrial deaths in the uk last year related to electricity.
I'm on the train now so can't get the domestic figures as the signal is as unreliable as the train...
But they are tracked and available.
User avatar
blinddrew
Jedi Poster
Posts: 8496
Joined: Sun Jul 05, 2015 12:00 am
Location: York
Ignore the post count, I have no idea what I'm doing...

Re: Troubleshooting Noise/Interference

Postby Hugh Robjohns » Wed Dec 11, 2019 11:27 am

cyrano.mac wrote:Sorry, Hugh, it's not extremely unlikely to have a bad ground.

I can't agree. In well over thirty years of working with mains installations in the UK I've only come across a handful -- certainly less than a dozen -- of occasions where I've discovered problems with mains grounding in building wiring. I'd count that as pretty rare. Obviously YMMV... (Sadly, the same isn't true in some of the far-flung corners of the world where I've worked. Some Malaysian mains wiring still sends shivers down my spine... :shock: )

However, when I'm working out and about I do always carry a tester and I always test sockets (and their ground impedance) before I use them because any safety earth problem is potentially a very serious one.

Unfortunately, the UK doesn't even bother to keep stats about electrocution.

Er... completely untrue. The Health and Safety Executive collect and publish records of all work-related injuries and fatalities, and their causes.

https://www.hse.gov.uk/statistics/causinj/kinds-of-accident.pdf
This 18/19 report states that 4% of 147 fatalities were caused by contact with electricity.

https://www.hse.gov.uk/statistics/pdf/fatalinjuries.pdf
And this one states there were 9 recorded fatalities due to electricity in UK workplaces in 2019.

The UK's Office of National Statistics also publishes data on all manner of things, including recorded deaths related to electricity, with data breakdowns on location (ie. home, residential places, industry, farms and so on). The figures for fatal electrocutions in England from 2001 to 2016 provide a total of 332... in 15 years.

https://www.ons.gov.uk/peoplepopulationandcommunity/birthsdeathsandmarriages/deaths/adhocs/007964deathsfromexposuretoelectriccurrentbysexandagegroupengland2001to2016

An older (1998) generic HSE report states: "Each year about 1000 accidents at work involving electric shock or burns are reported to the Health and Safety Executive (HSE). Around 30 of these are fatal. Most of these fatalities arise from contact with overhead or underground power cables...."

http://www.esldatasheets.com/Documents/HSE/ESaY_HSEPub_indg231.pdf

Although these figures are only for England, it's clear that fatal electrocutions is in the low tens, each year, at worst -- and that's tragic, obviously, especially as they are avoidable. But I find it hard to believe there were millions more in Scotland and Wales... so I don't know where your extraordinary figure of 2.8 million came from. It's simply not credible!

Our local regulations are among the most severe, but don't protect from sheer stupidity.

None ever could... as I said, education is the only way forward. Which is why I find it so sad that so many young people consider eschew science and technology these days.

By bridging audio and mains ground you are creating the environment in which these kind of accidents occur.

Er… no. That's utter nonsense... There certainly are situations where ground bonding needs careful consideration, most notably when working with non-standard mains supplies or equipment powered from isolating transformers... but these are not relevant in the hum-seeking context being discussed above.

You are exposing double insulated equipment to grounded equipment through the shield connection...

And what exactly do you think happens when you plug your double-insulated keyboard, or laptop, say, into a Class 1 stage-amp, or a class-1 mixing console, or a class-1 active speaker… ?

Class-1 devices almost always have the audio reference ground tied directly to the star earthing point along with the chassis and mains safety earth. Indeed, this configuration is strongly recommended as the 'best practice' for equipment grounding by the AES, no less.

Check out the diagram on page 5 of the AES48 documention, for example: http://www.aes.org/standards/comments/drafts/aes48-xxxx-190121-cfc.pdf (Sorry this is a draft version... the final document isn't publically accessible on the AES website, but the diagrams and recommendations are the same).

And the only reason some class-1 devices have a 'ground lift' switch with your beloved RC network is to avoid ground-loops when there are multiple interconnected class-1 devices.

All the 'grounding plug' is doing is replacing that tie to a real ground (that would normally be provided by a Class-1 device) in systems which comprise all double-insulated equipment and thus lack a solid ground reference.

I can assure you that I take mains safety extremely seriously -- both personally and in my role as Technical Editor of SOS -- and I certainly wouldn't suggest any practice that represented any potential risk. Bonding the audio reference ground of a double-insulated device to mains earth carries no risk whatsoever with normal working equipment, and nor does increase risks or affect the functionality of any conventional safety devices under fault conditions.
User avatar
Hugh Robjohns
Moderator
Posts: 25032
Joined: Fri Jul 25, 2003 12:00 am
Location: Worcestershire, UK
Technical Editor, Sound On Sound

Re: Troubleshooting Noise/Interference

Postby ef37a » Wed Dec 11, 2019 12:27 pm

Believe Hugh people!

Ste-c. Now that you know of at least one use for a modest digital test meter (others are...Phantom power check, battery check. You can even signal trace at line level with one) DO get one.

You could also throw a Martindale socket tester into the mix, whole lot should set you back no more than 30quid.

Dave.
ef37a
Jedi Poster
Posts: 10866
Joined: Mon May 29, 2006 12:00 am
Location: northampton uk

Next

Who is online

Users browsing this forum: Aural Reject