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Buzzing mic conundrum

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Re: Buzzing mic conundrum

Postby James Perrett » Sat Dec 16, 2017 7:55 pm

snipedog wrote: Did you have a grounding problem in mind that might account for this anomaly James?

As mentioned earlier, if the system relies on grounding via the USB connection it might be worth trying a ground wire from the RME case to mains ground.

Do you use power line ethernet? That can create radiated noise although it is usually at RF rather than audio. Other RF systems which use pulses of signal (like DECT phones) can also cause problems that might initially sound like mains. Old fashioned fluorescent lights and old CRT monitors are another source of noise. I'd be very tempted to switch everything off and then gradually switch things on one by one until you find the source.

Have you tried any electric guitars with single coil pickups? Do they buzz?
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Re: Buzzing mic conundrum

Postby snipedog » Sat Dec 16, 2017 11:57 pm

Hello James ,
Thanks for your help and perseverance!
There are no Ethernet on mains devices in the building, and no CRT monitors in the immediate vicinity. The first thing I did when I was asked to trace the problem was turn off the fluorescent strips in the room, so we are thinking along similar lines !
Strats and telecasters pickup the usual buzz when you stand next to the amp, but when DI'd there are no noise problems.
I have the same suspicions as you about the earthing through the USB connection for the Babyface, and I will make that the first test when we are next testing the system.
What puzzles me if that is a factor is why it would be a problem for both M5s, but not the other mics? The shell of the M5 seems to be connected to pin 1 in the usual way, the same as the other mics, so that shouldn't be a factor?
S
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Re: Buzzing mic conundrum

Postby Wonks » Sun Dec 17, 2017 12:34 am

There could be some paint or finish on the mic that is preventing a good ground connection. Maybe some of the finish needs to be scraped away in order to achieve this? A poke around with a multimeter might tell you whether the grille looks to have a decent low resistance path to pin 1 (though as that's painted/ceramic coated black as well it might be hard). It may well be that the black ceramic finish of the M5 shell and grille (compared to the nickel and chrome finishes of the NT3 and NT5) is providing a much higher overall ground path resistance which shows itself up when used with the snake.
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Re: Buzzing mic conundrum

Postby Hugh Robjohns » Sun Dec 17, 2017 12:42 am

If the suspicion is of defective screening around the mic capsule, which is obviously a possibility, you can check by wrapping the grille completely in tin-foil, and grounding that tin foil back to the interface ground. If the buzz goes away you'll know that poor grille grounding is the issue. If not, it's something else...

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Re: Buzzing mic conundrum

Postby ef37a » Sun Dec 17, 2017 7:40 am

Can we get a 20 sec audio clip of the buzz? .wav for preff..

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Re: Buzzing mic conundrum

Postby snipedog » Mon Dec 18, 2017 1:47 am

ef37a wrote:Can we get a 20 sec audio clip of the buzz? .wav for preff..

Dave.

Hello Dave, Im not sure how to attach a clip to the posting on the forum, but there is a short wav. file here;

https://www.dropbox.com/s/kap1s3ewzc93r ... z.wav?dl=0

Thanks

Steve
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Re: Buzzing mic conundrum

Postby ef37a » Mon Dec 18, 2017 9:54 am

snipedog wrote:
ef37a wrote:Can we get a 20 sec audio clip of the buzz? .wav for preff..

Dave.

Hello Dave, Im not sure how to attach a clip to the posting on the forum, but there is a short wav. file here;

https://www.dropbox.com/s/kap1s3ewzc93r ... z.wav?dl=0

Thanks

Steve

You can't attach NUFFIN in SoS forum (don't have the resources or sommat, I am a PC numpty) . I managed to download from Dropbox but no longer use it. I found it was grabbing 20% of my CPU and a shedload of ram, it also seemed mess with Prnt Scrn?

I never got handy with posting images and now I understand it is even more of a bother? I shall therefore have to describe your noise Steve.

It is a 'buzz' rather than just hum. 50Hz is present but is 6dB down on the main spike at 200Hz. 100Hz is some 3dB above 50 and the noise goes up the spectrum (Right mark) in 'perfect' order at 300,400, 500, 600, 700, 800,900 and 1000Hz when it gets even denser and messier. This really looks like mains hash pickup and Hugh's idea of screening or a lost earth seems very likely. Oddly, at 50Hz one channel is ~14dB down on the other but at 100Hz and above the channels match, pk for pk.

Have you tried running the mic with phantom power off? It is the LEFT ch that is up at 50Hz. (printer is B&W!)

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Re: Buzzing mic conundrum

Postby Dins4ever » Mon Dec 18, 2017 6:49 pm

Hi, Sorry I haven't read through all the details of this thread but you might like to hear my experience.
About 4 years ago i bought a matched pair of Rode NT55s from a UK dealer.
One of them had a buzz on it and they replaced the pair for me.
Sorry can't remember the technical details but I proved it was the mic just by swapping stuff.
I suggest you go back to where you bought it.
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Re: Buzzing mic conundrum

Postby Dins4ever » Mon Dec 18, 2017 7:58 pm

Just to add another thought to my post...
Additionally I think the packaging of my mics is a bit strange. I don't know what packaging you mic came with.
My mic pair came in a nice hard shell case. But the mic is squeezed held firmly in a slot of hard plastic which is directly coupled to the external shell of the case. Which means that if the case gets knocked in transit the knock is physically transmited directly to the mic.
This appears to me to not be the best way to package up mics for shipping. It would appear to me to leave the mic vulnerable to damage in transit.
:headbang:
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Re: Buzzing mic conundrum

Postby snipedog » Tue Dec 19, 2017 12:05 am

Dins4ever wrote:Just to add another thought to my post...
Additionally I think the packaging of my mics is a bit strange. I don't know what packaging you mic came with.
My mic pair came in a nice hard shell case. But the mic is squeezed held firmly in a slot of hard plastic which is directly coupled to the external shell of the case. Which means that if the case gets knocked in transit the knock is physically transmited directly to the mic.
This appears to me to not be the best way to package up mics for shipping. It would appear to me to leave the mic vulnerable to damage in transit.
:headbang:
Hello Dins4ever,
Thanks for your comments.
I have now been in touch with Rode, and they have today replied suggested that other users may have had a similar problem with these mics, and invited us to return them for testing / replacement?
I may never find out what the fault is that caused the buzz, but if it is within the M5's casings then that would explain our unusual findings, and it does suggest the earthing / screening inside the mic itself may be ineffective.
S
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Re: Buzzing mic conundrum

Postby Mike Stranks » Tue Dec 19, 2017 10:47 am

Well, the scheduled recording on Friday didn't happen (long and complicated story involving 'politics' in which I got caught in the crossfire. :( )

But the 'other users too' news from Rode causes a modicum of concern. Later today/tomorrow I'll set up some tests with various long cables and report back...
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Re: Buzzing mic conundrum

Postby Hugh Robjohns » Tue Dec 19, 2017 11:49 am

snipedog wrote:I have now been in touch with Rode, and they have today replied suggested that other users may have had a similar problem with these mics, and invited us to return them for testing / replacement?

Interesting... I'm glad you followed that suggestion! ;-)

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Re: Buzzing mic conundrum

Postby Mike Stranks » Tue Dec 19, 2017 4:14 pm

I've done some tests this afternoon, using both my M5s as follows:

Cheap 25m Pulse multicore unwound about 15 m. Tested both mics on various lines of the multicore.

30m single mic cable with both shells 'floating'. Again 15m uncoiled.

2 x 10m cables connected together. One 'decent'; one cheapish.

Connected to a cheapish analogue Behringer mixer and then to a QSC Touchmix 8. Both devices have an IEC (incorrectly called 'kettle-lead') connector with an earth pin.

All connections were balanced. Cables were deliberately routed within 1m of a wifi router.



In all cases there was nary a hint of buzz or hum. I had the gain and the headphones up to much higher settings than I would use in real-life.

Looking back through the thread I'm a little concerned that for the OP even with the NT3 and NT5 there was still some extraneous noise present. I've owned both of those in the past and used them many times in all sorts of environments and using all sorts of cables and gear. I never recall any problems which couldn't immediately be identified as a cable 'gone bad'.
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Re: Buzzing mic conundrum

Postby Hugh Robjohns » Tue Dec 19, 2017 4:59 pm

I share your interest, Mike. Unless I've missed it, I don't think we've had a report yet of whether the buzz was improved with a solid earth provided to the interface... and I think we need that before jumping to conclusions.
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Re: Buzzing mic conundrum

Postby snipedog » Wed Dec 20, 2017 2:05 am

Hello ,
Thanks again for your comments. Just to clarify the point about buzz when testing with the NT3s and NT5s. The buzz, )which I think I referred to as "at an acceptable level") , with those two mics, was only audible at very high monitoring levels, far higher than in normal use. I haven't had an opportunity to check the earthing via USB issue yet as the studio has been very busy over the last week and access has not been possible. However, over that week we have put the M5s away and continued to use the snake and the interface with a range of other mics, (LDCs, dynamics and ribbons with a Fethead) without encountering any hum problems. I hope to run some more tests once things get a little less busy ! S
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Re: Buzzing mic conundrum

Postby mat_171 » Sun Dec 09, 2018 5:59 am

Hi. I’m having the same issue with a pair of M5. Did you resolve this ground issue with the M5?
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Re: Buzzing mic conundrum

Postby snipedog » Sun Dec 09, 2018 3:25 pm

Hello Mat_171,
The M5's were eventually returned to Rode at their suggestion. However Rode sent them back with the problem reduced but not eliminated. We have since been replaced them with a pair of Rode NT5's as we gained the impression there is a fault in the design of the M5s. The coating on the outside of the mics might possibly be interfering with the earthing somehow, but we were not able to confirm this. S
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Re: Buzzing mic conundrum

Postby Wonks » Sun Dec 09, 2018 3:40 pm

Thanks for the feedback. A shame they couldn't cure the problem completely, but you've ended up with better mics.

I'd probably suspect that coating as well, though a simple multimeter test should have shown up any high resistance.
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Re: Buzzing mic conundrum

Postby Hugh Robjohns » Sun Dec 09, 2018 3:56 pm

I can't see how any coating on the outside of the mic would be a problem. But if the paint treatment got on the inside it could prevent an effective bond with the XLR pin1.

And I have come across other Rode's mics with various internal grounding issues.

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Re: Buzzing mic conundrum

Postby Wonks » Sun Dec 09, 2018 4:09 pm

The coating normally covers the screw thread holding the capsule on, which can reduce or prevent the capsule casing being grounded. And mic case ground bonding often seems to be down to the screw holding the XLR in place, which also relies on any coating on the body to be conductive.

If there was some conductive component of the coating that didn't get added to the mix before it was applied (or in too small a quantity to be effective), then it may be why just some M5 mics are problematic rather than all of them.
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