Do you live near a cell phone tower?
It's certainly not your typical USB whine. Sounds more like RFI from a digital source.
Does it also happen when the laptop is running on battery?
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 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)
If that foil trick worked a little, I bet its mostly RFI/EMI being picked up by poorly shielded cables/connectors.
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!
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 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.
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?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.
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?
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.