Hiss/Hum from Microphone?

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Hello all,

I've looked through a lot of posts in this forum about hum and hiss while recording, but I think that my situation is unique, so I'd really appreciate some troubleshooting help. I'm recording from a condenser microphone through an XLR cable into an ART Tube MP Project Series w/ USB preamp, and from there to my computer through a USB cable.

When I record guitar through this preamp with the volume as loud as it will go, I don't hear the slightest bit of hiss or hum—it's perfect. With the microphone, however, I hear a high-pitched hum. Here's the weirdest part: along with the USB input, I run an instrument cable from the preamp to the line-in jack of the soundcard so that I can monitor the input through headphones without any lag. When I listen through the headphones without recording and the Monitor VU-Meter is off, it sounds perfect. As soon as I click the “Monitor” button and the VU-Meter comes on, the sound starts. I thought I could just record then with Monitor off, but as soon as a click “Record,” the sound starts too.

Here’s a sample of the noise:
http://www.jasonblakely.com/nick/noise.mp3

Anybody know what's going on or how I could troubleshoot it? I would think it's the microphone or cable except that it sounds great when not monitoring or recording. I would think it's the USB line, then, except that guitar sounds great. I'm out of ideas.

Thanks in advance!

I presume you have “played” with the filter and gain switch combinations?

Do they give you any hint of help with this when you hit record?

I had this same sound when I did a project outside my usual room using a friends m-audio set up. In that case it ended up being a bad cable problem. A simple cord change did the trick.

Hope you get it fixed. These kind of things can be very discouraging.

Sound like digital noise from the motherboard to me. That said…

It’s possible that what’s being recorded is “what you hear” and when monitoring there is a bit of feedback from the monitoring back into what’s being recorded. Most of the time that would cause terrible squeal, but if the feedback is just a little or frequency depended, such as only very high frequencies, then the result can be this kind of sound.

As an example, I had an amp that would malfunction and go in oscillation. The frequency was in the 100khz range. That’s obviously above hearing range. It would regularly pop tweeters. It wasn’t until I put the amp on a scope that I figured out what was going in. The reason the amp did that was because some filters in the amps feedback loop (most amps have these) was screwed up. It was an old amp and some capacitors had started breaking down. That was an analog thing.

It’s possible that something similar is happening in the analog part of the preamp or soundcard. Higher than audible range or nyquist frequency sounds MUST get filtered out or the sounds can’t be successfully converted to digital. If there is a low level high frequency component to the audio it can sound like what you are hearing, and it most likely won’t be audible in the original analog audio.

THAT SAID…

It still sounds like digital noise from the motherboard to me. :)

phoo,

Forgive my ignorance but if the motherboard was the source shouldn’t he hear it when recording guitar through the same set-up as well?

I’m wondering if it might be a phantom-power issue. My suggestion would be to test out other microphones (condenser and dynamic) and see if you get the same results.

I didn’t say it WAS digital sound, only that it sounds like it. :)

I like your thoughts, Bill.

I don’t really have a clue what it really is. There’s not really enough to go on. I think process of elimination is going to be needed.

Is the noise not there when recording with the mic but monitoring is off?

Is it there when the guitar’s level is lowered WAY down.

Is it there when using some other source into the mic input - something that doesn’t require phantom power, or better still, isn’t a microphone, like a line out from an amp?

Hi, It sounds like a ground loop problem to me. I have heard similar noises from an Edirol usb interface and phantom power made them worse. Are you using a laptop computer, if so is it the same if you run on batteries with the mains unplugged? Does it still do it if you remove the cable to the soundcards line in jack? Try temporarilly unplugging any leads from the output of the Art pre that go to your monitoring, if that fixes it one of these in those leads would probably solve the problem. http://www.zzounds.com/item–BEHHD400
Nick

Thanks for the tips, everyone! You people are great.

I’ve tried playing with the filter and gain switches to no avail.

I thought it might be motherboard noise, too, BUT I tried using a really cheapo mic (dynamic) through the 1/4-inch instrument jack and can crank the volume up all the way with no noise at all! What does that mean? Does that rule out motherboard noise? Does this mean it’s probably the mic cable, as Poppa Willis suggests?

And phoo, the noise does appear when recording with the monitor off. It’s not there with the guitar level way down. I don’t have any other object that I can plug into an XLR cable besides this microphone.

And nick, I AM running on a laptop and have tried running it with the computer unplugged and with nothing else running in or out of the preamp. HOWEVER, I can’t run the preamp itself with it being plugged in, so could the ground loop problem be coming from the preamp power itself? Is there a way to test this?

Thanks again, good people!

Okay…what happened? I was playing with the audio settings (in nTrack and in Windows). I thought I put them back where they originally were, and now the sound is gone! I wrote down all the current settings, but now I can’t even recreate the sound if I try! I can still here it with the monitor on, but it’s no longer recording the sound itself. This is crazy. I don’t know how long it will stay like this, but it’s good for now!

Since you say you changed something within the computer and it stopped my guess is that that is where the problem was to begin with.

As others have suggested it seemed like your monitoring set up was creating the problem, and it WAS being recorded.

Now that you are not “recording” from that source (or that source is not being “included” in the input of the recording) it’s mute.
However, the problem (hum) is still there…as you said you can hear it while monitoring. (which over time can be VERY annoying)

Which does sound like a grounding issue as also suggested between the computer, and the interface and it’s power supply.

There are ways to get rid of that one just needs to research other error reports on the net for that device, and good Ol’ google.

I remember a thread a while back here about “power conditioners” not sure if that has anything to do with your issue though…

keep shinin’

jerm :cool: