Highpitched whining noise; how to get rid of it?
- Thread starter ErikVerkoyen
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ErikVerkoyen
New member
Battery or plugged in makes now difference and I only get it with mics, recording line in is no problem; I tried out a lot already.
The recording is with the mics pointing in the corner where the noise is worst and the gain fully open.
In practice it's more like a faint background noise and sometimes it isn't there at all.
I do live in a typical Amsterdam situation with neighbours left right and under me who all probably have wifi and whatnot.
Gtoboy
Well-known member
Rfi from some type of device with a motor would be my guess, although as I mentioned , some poorly shielded video/television screen drivers can do this also. As well as nearby radio or cell towers. This can be difficult to shield from without causing more harm. Some mics are better shielded that others. You can try rigging up your own "shielding" on the mic bodies using metal foil. May or may not help, will definitely look goofy but cheap and harmless if it doesn't help. Try to find a time pattern so you can record when the least RF is happening. As a last resort there are plugins that can help reduce this kind of noise, though far from perfectly or transparently. You could try recording just the noise on one track and reversing it's phase then blend with recorded track to see how much cancels. Total long shot on that one.
cyrano
Member
If the mlc is the cause of picking up RFI, it could be solved with a pair of 10 to 47 pF capacitors from pin 1 to pins 2 and 3, as close as possible to the XLR pins inside the mic. But these should already be present. Have you tried different cables?
I'm guessing one of your nearby neighbours has a bad wireless DECT phone. Or a nearby cell tower is beaming into your appartement. In both cases, you might want to complain to PTT (dienst radiostoringen). Especially if it happens with all or most condenser mics. In general, it's seldom Wifi.
I've had a case in Brussels where everything audio was making faint noises like this. Guitar amps, mic preamps, mixer... It took six months but they finally came to measure. About three weeks later, the antennas on the cell tower about 500 meters down the road were redirected and all trouble went away. In this case, no capacitor or ferrite bead was able to keep the RFI out.
Have you talked to your neighbours? If a few of you complain, you'll get results faster.
I'm guessing one of your nearby neighbours has a bad wireless DECT phone. Or a nearby cell tower is beaming into your appartement. In both cases, you might want to complain to PTT (dienst radiostoringen). Especially if it happens with all or most condenser mics. In general, it's seldom Wifi.
I've had a case in Brussels where everything audio was making faint noises like this. Guitar amps, mic preamps, mixer... It took six months but they finally came to measure. About three weeks later, the antennas on the cell tower about 500 meters down the road were redirected and all trouble went away. In this case, no capacitor or ferrite bead was able to keep the RFI out.
Have you talked to your neighbours? If a few of you complain, you'll get results faster.
It does have some of the hallmark of USB noise? The 1kHz spike and then more spikes at exact intervals.
I am more concerned about the underlying crackle? This smacks to me of a poor earth/screen connection in a mic cable but if you have tried various mics then I dare say you have tried more than one cable? If not a cable then perhaps a bad joint inside the AI.
Assuming you have mics and cables can you run two, one in the 'offending' part of the room and one in another? Maybe post a rough diagram of the room and mic positions? Please post as two separate MP3s.
Never tried it (will now!) but maybe Google Earth will tell you if you have a phone TX nearby?
You could try some clip on ferrites on the mic leads but I doubt they will stop crackles.
Does the USB cable have a 'lump' on it? If not might be worth trying one.
Dave.
I am more concerned about the underlying crackle? This smacks to me of a poor earth/screen connection in a mic cable but if you have tried various mics then I dare say you have tried more than one cable? If not a cable then perhaps a bad joint inside the AI.
Assuming you have mics and cables can you run two, one in the 'offending' part of the room and one in another? Maybe post a rough diagram of the room and mic positions? Please post as two separate MP3s.
Never tried it (will now!) but maybe Google Earth will tell you if you have a phone TX nearby?
You could try some clip on ferrites on the mic leads but I doubt they will stop crackles.
Does the USB cable have a 'lump' on it? If not might be worth trying one.
Dave.
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ErikVerkoyen
New member
Thanks for the answers so far!
I did some tests wrapping aluminium-foil around the mics and the cable-ends and that helped a lot to my surprise.
I will probably search for some cables shielded against this kind of interference. I did find some info on neutrik xlr audio connectors that seemed like it could be the right thing but I would prefer to find some complete cables that I can purchase here in Amsterdam, try out and return when they don't make a difference. Any suggestions on that appreciated.
I live in an apartment-building in the middle of Amsterdam so there is likely all kinds of interference. A bad wireless DECT phone seems likely. But apparantly there is also a 4G mast on the building across the street (according to another site I found) It's listed with the following details:
height:
27.3 m
freq:
1860 MHz, 950 MHz, 2144,7 MHz
Power:
33 dBW
(PTT and Dienst Radio-storingen don't exist anymore I'm afraid)
I did some tests wrapping aluminium-foil around the mics and the cable-ends and that helped a lot to my surprise.
I will probably search for some cables shielded against this kind of interference. I did find some info on neutrik xlr audio connectors that seemed like it could be the right thing but I would prefer to find some complete cables that I can purchase here in Amsterdam, try out and return when they don't make a difference. Any suggestions on that appreciated.
I live in an apartment-building in the middle of Amsterdam so there is likely all kinds of interference. A bad wireless DECT phone seems likely. But apparantly there is also a 4G mast on the building across the street (according to another site I found) It's listed with the following details:
height:
27.3 m
freq:
1860 MHz, 950 MHz, 2144,7 MHz
Power:
33 dBW
(PTT and Dienst Radio-storingen don't exist anymore I'm afraid)
cyrano
Member
A sign that you're dealing with RFI, at 1 GHz or higher..
It could also carry DVB-T transmitters. These can easily cause nearby RFI, mixing with the 4G frequencies. That can be tuned out by the operator, if you can get them to act.
Yes, of course. We still use the old names
Have a look here:
Melden storing draadloze apparatuur | Contact | Agentschap Telecom
I've got no idea if they still take consumer complaints seriously. But they used to. Allow time for the complaint to drizzle through. In Belgium it takes 3 to 18 months. And sometimes a problem can't be fixed.
Indeed. I would makeup some XLR mic leads using foil screened cable. Not quite as flexible as braided screens but gives 100% shielding. Give the connectors and the part of the mic body where it contacts the XLR case a good scrub and a splash of cleaner (Dox-it if you have it but WD-40 will do).
It is normal practice NOT to connect XLR shells to pin 1 but in your case I would try it. If you do make up some cables, buy some ferrite rings and thread as many turns as you can through them, one mic, one AI end.
The main problem is that it is the equipment that should be RFI proofed. Palliative measures 'outside the box' are often ineffective. I always cringe when I read a review of a mic pre say where the maker boasts a response to "over 200kHz" WTF for!
Dave.
ErikVerkoyen
New member
Getting shielded mic-cables seems to have done the trick though. I bought these :
Sommer Cable Galileo 238 5,0 – Thomann Nederland
...and now the noise is mostly gone (if I crank up the gain to the maximum and point the mics in the worst corner of the room I still hear it faintly; but in normal use it's gone)
Thanks for all the suggestions!
That cable is about the right price, be about £30 here for 5mtrs of good quality cable and Nookies.
I shall repeat my point about RFI being best stopped 'in the kit'. I am willing to bet that a ferrite ring choke and a few caps INSIDE that mic would stop the RF dead. I will also bet it does not have them!
The marketing boys L.U.R.V.E. their extended responses! Tell a customer an amp is 0.2dB down at 20kHz and he will think twice. Leave out a few caps and say "Flat to 45kHz and they will have your hand off!
And WTF anything small signal, music audio needs to be DC-coupled I cannot imagine!
Ananother thing! Way ago most mics, including capacitors, had output transformers. Now if there is one thing RF hates its a transformer with an inter-winding screen. Again,"transformerless" is touted as highly desirable. Ain't necessarily so. CHEAPER tho'but.
Dave.
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cyrano
Member
That about sums it up, Dave. Just two 10...47 pF caps ON the XLR in the mic fixes 99% of the RFI misery. An astounding number of mics don't have those.
And transformers are even a lot better, because of intrinsically high CMR (common mode rejection). Any sort of noise coming onto the balanced connection is simply eaten by the transformer, since it isn't balanced. Any asymmetrical signal is shorted by the transformer. Of course, trannies are expensive. And good trannies are even more expensive.
Dynamic mics are also inherently less susceptible to RFI noise. These don't even need a transformer. It's the electronics in condenser mics that sometimes ruin your day.
And transformers are even a lot better, because of intrinsically high CMR (common mode rejection). Any sort of noise coming onto the balanced connection is simply eaten by the transformer, since it isn't balanced. Any asymmetrical signal is shorted by the transformer. Of course, trannies are expensive. And good trannies are even more expensive.
Dynamic mics are also inherently less susceptible to RFI noise. These don't even need a transformer. It's the electronics in condenser mics that sometimes ruin your day.
I am beginning to wonder about you Cyrano? Transformers to not stop RF because of the CMMR, that only works for audio frequencies. It is primarily the inter-winding screen (if fitted) that does the bizz. Even transformers without a screen stop quite a bit of RF because of the capacitance to frame.
Dynamic mics of any decent quality use a transformer because the optimum diaphragm coil impedance is likely not close to the standard output impedance of 150R in US and 200R in EU. In practice the OPZ of mics is a bit of black hole but they are mostly close to the specified figure.
Then, quite a number of dynamics have hum bucking coils or transformers and some LC frequency response modifiers. Most famous one of course being the SM7b.
Dave.
arcaxis
Well-known member
A mic cable may typically have conductor capacitance to its shield(ground) of about 80pF/m. With the inherent capacitance of the cable, what would the addition of caps inside the mic gain, assuming your intention is to couple pins 2 & 3 through the caps to pin 1?
cyrano
Member
I didn't write that, Dave. Take a good look. I wrote "noise". Now maybe it's the "any kind" that set you on the wrong leg. I'm sorry for that.
And those two tiny caps sure as hell are there to help stop RFI.
Don't you think the transformer would transfer less RF energy than a straight wire?
And those two tiny caps sure as hell are there to help stop RFI.
Don't you think the transformer would transfer less RF energy than a straight wire?
I was not "put wrong(ly!) " The phrase "any noise" includes RF noise.
"Don't you think the transformer would transfer less RF energy than a straight wire?"
Don't know, the combination of stray inductance, winding to winding capacitance might at some RF frequency pass MORE energy than a certain length of wire.
RFI stopping can be peculiar to a place, field strength, frequency and of course the equipment affected. I 'grew up' with the Transistor and when Silicon Planar types hit the streets all kinds of RFI hell broke loose! I live only a few tens of clicks from both Rugby and Daventry. Google their radio history. Keeping RF out of audio was something that kept me busy. (and we won't even mention the rise of the taxi driver's PMRs!)
THEN! We had the great 27meg CB explosion. My point is, I did quite a bit of fixing RF ingress into audio.
So, audio transformers don't work much past 60kHz and therefore CMMR is meaningless at RF cos' you no longer have transformer action.
Dave.
"Don't you think the transformer would transfer less RF energy than a straight wire?"
Don't know, the combination of stray inductance, winding to winding capacitance might at some RF frequency pass MORE energy than a certain length of wire.
RFI stopping can be peculiar to a place, field strength, frequency and of course the equipment affected. I 'grew up' with the Transistor and when Silicon Planar types hit the streets all kinds of RFI hell broke loose! I live only a few tens of clicks from both Rugby and Daventry. Google their radio history. Keeping RF out of audio was something that kept me busy. (and we won't even mention the rise of the taxi driver's PMRs!)
THEN! We had the great 27meg CB explosion. My point is, I did quite a bit of fixing RF ingress into audio.
So, audio transformers don't work much past 60kHz and therefore CMMR is meaningless at RF cos' you no longer have transformer action.
Dave.
cyrano
Member
Yes, but that capacitance isn't at the entry point where the RF gets into the mic's electronics. And it is dependent on the length of the cable and the quality, so it might not work always well.
cyrano
Member
Resonance. I considered that too. Even the straight wire can be resonant, if the frequency is high enough.
I used to have a neighbour with a 50 W cheap italian "stove" on hist CB. Came in through the phono input pf my amp. I put ferrite beads on it, that solved it mostly. Then he got a 150 W amp...
I just wired up a 100 mW 27 MHz emitter with a directional antenna, aimed at his antenna after that, cause even the beads didn't stop it. He still could emit 150 W, but he couldn't receive anything. Solved it. After a few days, I dismantled the little receiver. He probably knew, but he also knew he was legally limited to 4 W.
I'm not very well versed when it comes to audio transformers. Just recently realised these things don't have an impedance of their own, fi. Makes thinking how they'll react a bit hard. Not a problem. The stuff I check and repair is pretty low-end, so it seldom has any transformers.