Problem with mic or cable?

[elicross]

Hey, all - I'm trying to figure out if there's something wrong with my microphone or its cable.

I've been trying to record some clips of the Tweed Champ, but I'm getting a hum from the microphone. I made a clip to illustrate the problem.

The first ten seconds and last five seconds of the clip are with my guitar turned all the way down, and the guitar I'm playing is a Deluxe Player with Vintage Noiseless pups, so there's little to no hum coming from the guitar itself. It's not coming from the amp, either. It's only present when I'm recording or monitoring the signal from the mic.

http://soundclick.com/share?songid=6296479

The hum goes away if I turn my interface's mic gain way down...but then I'm not getting enough signal to record. As you can hear in the clip, even with all this hum from the mic, the guitar/amp's level is not really high enough.

The mic is a used SM-57. The cable is a new no-name with Belden wire and Neutrik connectors. The mic's on a little stand, its head nearly touching the grille of the amp. It's positioned almost at the edge of the speaker cone and angled slightly toward the center of the cone.

The amp's turned all the way up, and so is the guitar. It's pretty loud in the room.

Thanks for any thoughts on this.

[Mesotech]

That particular static type hum typically comes from running a mono jack into a stereo input. One side of the input is shorted to ground, and the other side is receiving the signal.

Try monitoring the input one side at a time to see if the noise is present on both sides, or only on one side. If only on one side (and that side has no other sound except the hum) then you know where the issue lies.

In such a case, try to record in mono and select the side with signal.

[elicross]

Thanks. Can that happen with a low-Z mic cable with XLR connectors?

The way I've got things hooked up now, the mic is plugged into the XLR input of my M-Audio Black Box, and that's connected via SPDIF to my sound card. In Sonar, I tried using the SPDIF Left, Right, and Stereo inputs to see if that made any difference, but the hum is there regardless.

Is it possible I have the wrong type of mic cable...or is there only one kind with XLR connectors?

[Mesotech]

If the mic cable is XLR, and you're going into the computer with SPDIF, then one side being grounded is probably not the case at all. I wouldn't suspect cables at this point.

The next most obvious place to look would be the preamp. I have a little Behringer Xenyx 802 mixer that I bought to inject mic signal into my computer's audio inputs. It seemed to work great, until I recorded. That's when I noticed a definate hum. Upon further investigation of the hum through signal analysis, it turned out the hum wasn't hum at all, but interference from the switching power supply that came with the mixer being picked up by the mixer's preamps. I changed mixers to a Mackie 16 channel, and never had the problem again. I figured that I'd just relegate the little 802 to stage use as a keyboard mixer, but the switching power supply was really bad when connected to the PA.

I'm not sure what the next best way to troubleshoot your noise issue might be, without replacing different components of the chain with something alternate. I just so happened to have something available to swap things around, and it helped to isolate the problem component.

[elicross]

Well, I moved the interface (an M-Audio Black Box) to the same electrical circuit as the amp and computer, and it seemed to reduce the hum I was getting. Might have had some kind of ground loop problem.

But I've still been struggling off and on for about a month, trying to make a recording that sounds as good as what I'm hearing in the room.

I'm back to thinking the mic is faulty. The output just seems way too low, even with this 5W Champ going full blast and the mic right up against the amp's grille. Last night, as an experiment, I tried recording the amp using a cheap headset mic designed for online chats, propped up about a foot from the amp and plugged right into the sound card...and I got a much stronger signal and better sound than I'm getting with my used SM-57!

That can't be normal, can it? There's got to be something wrong with the mic, the cable, or the Black Box's XLR input, right?

Is there any way to test these components with gear I have on hand, like a simple multimeter?

[Mesotech]

I'm not certain if you have a music store anywhere close.

You can test the cable with a simple multimeter easily enough. Test for continuity on each pin from one end to the other, then test for shorts between the pins. An XLR pin out should be readily available on the net somewhere.

Provided the cable tests good, take the cable and mic to a local music store and ask to hook it into a floor model mixer to see if it's working properly. They'll also have another cable handy just in case yours tests bad at the store. You'll be able to tell if the mic is bad, or the cable. If neither is bad, you probably have a bad interface.

[Mikey]

It might just be that you've got the mic cord to close to a power cord someplace. Try separating the signal cords to one side away from the power cords.