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Buzzing mic conundrum

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Re: Buzzing mic conundrum

Postby snipedog » Fri Dec 15, 2017 3:04 pm

Thanks Hugh,
That gives me a few more things to check. I've flagged a query with Rode via their website.

If there is indeed a problem with the M5 driving longer cables I would expect other users to have come across it. The environment we are using the mics in is not particularly EMI or RF "hostile".

The M5s are electrets rather than "true" condensers, but their output is around the same as the NT3 so I can't see that being a relevant factor.

I have my suspicions about the earthing of the screening in the snake as Ive never thought USB leads made a very convincing connection. If the only route for the screen to earth is via the Babyface USB lead and into the computer to the mains earth that seems a bit fragile to me, so I'll start there with the next fault finding session. That still doesn't explain why the NT3 and NT5 are not affected by that, but I need to start somewhere !
Thanks again
Steve
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Re: Buzzing mic conundrum

Postby John Willett » Sat Dec 16, 2017 12:29 pm

Talking of the Babyface ...

Synthax UK are doing a special deal at the moment for all those who have a Babyface to upgrade to the Babyface PRO at a special price.

See HERE :thumbup:
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Re: Buzzing mic conundrum

Postby snipedog » Sat Dec 16, 2017 2:28 pm

John Willett wrote:Talking of the Babyface ...

Synthax UK are doing a special deal at the moment for all those who have a Babyface to upgrade to the Babyface PRO at a special price.

Hello John,
Thanks for the pointer, it is actually the Babyface Pro we are using! Maybe I should have specified that, but I didn't realise there was an older version. S
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Re: Buzzing mic conundrum

Postby James Perrett » Sat Dec 16, 2017 5:42 pm

snipedog wrote:The puzzling bit is if I remove the M5 from the connection through the snake, and replace it with an NT5 or an NT3 (but change nothing else at all, even the cable remain in the same place!) the buzz level drops to an acceptable level (almost inaudible)

I must admit that I'm a little worried by this comment. I wouldn't expect to be able to hear any buzz at all in a properly working system - just hiss from the microphone or preamp. Is this an area of high interference or is there a grounding problem somewhere?
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Re: Buzzing mic conundrum

Postby snipedog » Sat Dec 16, 2017 5:54 pm

James Perrett wrote:
snipedog wrote:The puzzling bit is if I remove the M5 from the connection through the snake, and replace it with an NT5 or an NT3 (but change nothing else at all, even the cable remain in the same place!) the buzz level drops to an acceptable level (almost inaudible)

I must admit that I'm a little worried by this comment. I wouldn't expect to be able to hear any buzz at all in a properly working system - just hiss from the microphone or preamp. Is this an area of high interference or is there a grounding problem somewhere?

Hello James,
Thanks for your input. I agree entirely there shouldn't be any audible buzz in the system, but it becomes clearly audible with the M5's connected. Wiith the NT3's or 5's the monitoring volume has to turned up very high (well beyond normal monitoring volumes) in order for any 50 Hz buzz to be audible at all. (This is what I meant by "an acceptable level"). I suspect you are right, and there is a grounding problem somewhere, but I can't identify it in the tests on the wiring Ive done so far. If there is one its having such an effect on the M5s as to make them unusable for recording solo piano, but having very little effect if any on the NT3s and the NT5s ? As I mentioned in the earlier posts, this is not an RF or EMI "hostile" space, there are no phone masts nearby, the mains wiring in the building looks to be less than 25 years old, and nobody is using arc welding kit nearby! The interference is a steady 50Hz (plus harmonics) with no audible spikes or "digital fizz". Did you have a grounding problem in mind that might account for this anomaly James?
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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...

H
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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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