[geoff]

On 8/09/2018 6:30 AM, John Williamson wrote:
On 06/09/2018 19:23, Mike Rivers wrote:
On 9/6/2018 1:02 PM, John Williamson wrote:
If the interference is from a cell tower a block away, then it is RF

RFI is a special case of EMI. They're both electromagnetic radiation.
What you get from a power line or a wall wart is interference from
electromagnetic induction.

Picky, picky.

Not really. What I call EMI is usually low frequency, directly induced
in the coils, while RFI is a modulated higher frequency, which normally
only affects circuits with a semiconductor or other rectifying component
in them, such as a preamp.

I find it a useful distinction to draw, as the cures are different.

The OP describes a hum or a buzz, rather than the typical "chirping"
sound of a cellphone being picked up, so I was guessing at LF, possibly
from a choke, fluorescent light or (Unlikely) a SMPS near the
microphone, which doesn't have a humbucking coil. It's hard to get
interference from cellphone transmissions, even from base stations, more
than a few feet from the microphone due to the low power and inverse
square law of propagation, though an experienced movie sound guy can
often tell what make of cellphone is about to ring on set.....



Could be from a laptop SMPS , especially if the noise problem is that it
is showing on a recording (rather than live). If on a recording only,
try the laptop on battery-only, to confirm.

geoff

[mcp6453[_2_]]

On 9/7/2018 8:47 PM, geoff wrote:

Could be from a laptop SMPS , especially if the noise problem is that it
is showing on a recording (rather than live). If on a recording only,
try the laptop on battery-only, to confirm.

I'm still not clear on the source of the noise. However, it's safe to
say that the noise is electromagnetic. I found a couple of like-new EV
N/D 767a mics at my local Guitar Center for $69 each, so I bought them.
They have humbucking coils in them and are totally quiet. Their sound
was also quite decent. They'll do until the broadcaster can spring for a
couple of Heil PR40s.

[Phil Allison[_4_]]

mcp6453 wrote:



I'm still not clear on the source of the noise. However, it's safe to
say that the noise is electromagnetic. I found a couple of like-new EV
N/D 767a mics at my local Guitar Center for $69 each, so I bought them.
They have humbucking coils in them and are totally quiet.


** The correlation between having a humbucking coil fitted and being noise free in the office room appears 100%.

The odds are high that an adjoining room or one above or below is used for AC power distribution, is fitted with high current cabling and a switchboard.

Wherever Active and Neutral conductors travel separated rather than running in close parallel, the external magnetic field generated is much greater than usual - easily enough to cause the hum interference you have described.



..... Phil

[Scott Dorsey]

mcp6453 wrote:

I'm still not clear on the source of the noise. However, it's safe to
say that the noise is electromagnetic. I found a couple of like-new EV
N/D 767a mics at my local Guitar Center for $69 each, so I bought them.
They have humbucking coils in them and are totally quiet. Their sound
was also quite decent. They'll do until the broadcaster can spring for a
couple of Heil PR40s.

No, it's magnetic, not electromagnetic. There's no e-field involved, and
consequently you can use the microphone itself as a sensor to hunt down the
source of the problem.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."