What Is Causing This Noise?

S

soundchaser59

Reluctant Commander
I record my guitar cab with an SM7b. But tonight I noticed a strange noise in the phones, and I isolated it to the SM7b channel. Even if I turn the guitar amp off, I still hear this noise. There are no effects on, just SM7b into the (Emu 1616m pci) mic input, straight to Sonar. I put a Heil mic in front of the guitar speaker as a test and it did not pick up anything, so I know this noise is coming thru only on the SM7b channel. I have not done anything else to isolate it, but wonder if anybody has heard anything like this before?

If I sit there just listening, this noise happens roughly once every minute. The interval is not consistent, sometimes a minute, sometimes a bit longer, sometimes 30 seconds or so, etc....and it sounds slightly different every time it happens, sometimes shorter, sometimes a bit longer, usually just once but sometimes twice or three times in a few seconds, etc..... There are no motors or anything like that in the house. I have no idea. This just started tonight and last night.




Any ideas? It isn't very loud, but it does get recorded...... :confused:

Almost sounds like a bug like a small moth trapped inside the SM7b capsule....:rolleyes:
 
I suspect it's a variation of GSM chirp. For some reason, the frequency component is getting damped and you're just getting the switching pop. This is an artifact of GSM cellular phones and the way they switch on and off their transmitter at a particular frequency while identifying themselves to the tower and while sending and receiving data (but not voice, oddly enough).

Try taking your cell phone out of the room when you record and see if the problem goes away.
 
the person with the cell phone will be gone all day today. Be interessting to see if the noise returns when she does!
 
Yep it's a cell phone. When my brother is in my truck I can tell when he's about to get a call because that exact same sound comes thru the radio.
 
That's funny, because I have the 1616 pci into a pcmcia adapter. I have my phone on in my studio all the time and I never get that interference. Check your xlr cable. Try the amp again with the Heil in front of it when you know shes on the phone. I don't think it's going to be exclusive to the Shure. Good Luck.
 
The person with the cell phone left and the noise continued. I siwtched the mic cables left and right, but the noise continued to be in the left input. I put the phones into the mic preamp and there was no noise at all. So I knew the noise was not coming from the mic or the mic pre. It had to start at the Emu dock.

You guys talking about wireless stuff got me to looking more closely at what is going on in my studio. Since my Sonar machine is in the basement but I need to authorize software, etc., I use the wireless connection to my router upstairs.

The 1616 dock has two mic inputs on it. A couple days ago I changed my wireless configuration and I set the computer's little 3 inch tall wireless antenna on top of the Emu dock, directly above the left mic input. Didn't give it a second thought. Then I remembered that the wireless connection will periodically (probably about every 60 seconds) "talk to the router" to make sure it is still there and the key code is still valid.

So, by watching this little systray icon.....
wireless_emi.bmp


I noticed that the noise in the left input only happened when the green "network communication" light comes on in the systray icon. I waited for it to happen again, and as soon as I moved the little antenna away from the dock, the noise disappeared.

Whoda thunk it? Your hints about wireless EMI set me up to figger this one out! So THANKS people!! :D
 
Naaawww..... you guys weren't wrong, you had the wireless idea right, just fingered the wrong wireless device. Same principle, though..... it put me on the right track! :cool:
 
The funny thing is that I almost said, "Or Wi-Fi", but thought about it and concluded that the emissions from a Wi-Fi device could never cause that in practice because they don't slam the carrier on and off rapidly like GSM devices do. They're spread spectrum, not time domain.

Of course I wasn't even considering that you might put a transmitting antenna an inch from your audio hardware with a wireless driver that aggressively manages transmit power.... Yeah, I could see that being a problem. :D
 
Which begs the question, WHY ONLY the SM7b channel? I think that it's more of a cable / shielding issue. Or else it would affect ALL channels. It could also be the mic. Or that specific channel on the interface/preamp. You've identified the source at least. Although networking WHILE recording tends more towards realtime priority with clicks and pops, not handshake stuff.

Now that I downloaded it, it sounds a bit like a rotary phone, not a cell phone. I used to get something like that if my cheapo electret ran the cable near the display device. I tend to disable networking devices if I'm doing anything critical with audio. But that's a lot easier to do in Linux than Windows.
 
Shadow_7 said:
Which begs the question, WHY ONLY the SM7b channel? I think that it's more of a cable / shielding issue. Or else it would affect ALL channels. It could also be the mic. Or that specific channel on the interface/preamp. You've identified the source at least. Although networking WHILE recording tends more towards realtime priority with clicks and pops, not handshake stuff.
Click to expand...

Probably has something to do with higher gain on that channel, what with it being a dynamic mic and all. That and possibly proximity to the jack.
 
You must log in or register to reply here.
Back
Top