Nasty noises when recording to a computer?

April 11, 2008 3:57 PM

Recordingfilter: Why do strange buzzing noises and "zzzt"s appear when someone isn't touching the guitar strings while recording on a computer.

I've had this happen in several studio setups (all recording to a computer with different software) in several houses in different locations with several guitars/basses.

In a former house that was old with some iffy wiring in places, I noticed that sitting in front of the computer could cause it (which I figured was the monitor, and was right), the heater coming on, or sometimes even just a glitch with the computer. This was going direct and with a mic/amp setup using an older SG. The SG is a little noisy anyway, so that was easy to understand and fix.

A few months ago in a basement studio, however, I noticed that the same problem would happen in a mic/amp situation and the computer was in another room. Recording bass (Rickenbacker) through an amp with a mic was the worst with many strange "zzzt" noises when the bassist's fingers moved from the strings. I chalked it up to weird wiring in the house, but it turns out that the owner of the studio had an electrician come look at the wiring (for a separate reason) and the electrician said that all of the outlets were grounded and in working order. Also, recording guitar in a mic/amp situation, the pickups on the guitars I was using (an older Epiphone hollowbody, a newer Ibanez hollowbody, a tele, and my SG again) would buzz if I was facing the computer, which was in another room separated by a wall with some of the outlets on the same wall and a few on another.

Has anyone ever had this problem or anything similar? Is there a way to fix it without rewiring an entire house? Would a noise gate work to get rid of the strange noises when a hand moves from the strings? Is it old pickups vs. computers?

All I know is that it drives me crazy and once I think I have it fixed, it comes back or we switch locations. Please let me know if I'm not clear enough on the noises that I'm hearing and I'll try to find some examples later.

Thanks.

posted by sleepy pete to media & arts (12 comments total)

Computer may not be shielded as well as a regular recording console unit that is purpose-built to record.
posted by Ironmouth at 4:14 PM on April 11, 2008

I don't think there's a simple answer here -- in a studio with a computer, there are quite a lot of places where noise can be picked up and amplified. I'll address a few of the first ones:
- First of all, CRTs generate a fairly large electromagnetic field, and your pickups will sense these pretty easily.
- All of the cables and internal power+logic circuitry for your computer are rated for digital signals, so they're expecting high-frequency 0's and 1's; this means they focus more on keeping those specific frequency bands clean and isolated rather than designing for an analog (balanced) audio signal.
- It could also be something along the path from your pickups to the computer's analog-to-digital convertor (ADC) that's coupling with the fields generated by the rest of the computer; e.g. if the internal wiring from the preamp to the ADC is not shielded well, it will pick up extraneous interference.
- One other possibility (and this one is a longshot, so take it with a heavy grain of salt) is that the strings themselves are acting like antennae, and coupling with whatever's in the room.

I've had similar issues that you have (although more with XLR cables on condensors), and I just try to make small faraday cages for long cables. That is, I have a metal box that I shove the XLR cable into; it helps a bit with the SNR. You just have to remember that you're swimming in a sea of electromagnetism, oscillating at different frequencies and powers. Given that there's only so much manufacturers can do within their budgets, and especially considering open-coil pickups, after a certain point, you just have to accept the noise.
posted by spiderskull at 5:05 PM on April 11, 2008 [1 favorite]

I've been told that the root cause of this is a grounding issue somewhere in the instrument or amp, but I've also noticed that it gets worse when I'm using unshielded cables. Doubly so while around devices that emit strong magnetic fields. (Monitors, TVs, etc.)

/not a recording engineer.
posted by lekvar at 5:18 PM on April 11, 2008

Note that the computer seems to be the only common element here. Try another computer.
posted by Ironmouth at 5:43 PM on April 11, 2008

Hey, thanks for the answers so far everyone.

spiderskull, I was afraid of that (that being "I don't think there's a simple answer here"). I've often wondered if it's a battle that can never be won until I can afford to just set up a dream studio, but since that's a "dream" studio it won't happen soon.

Ironmouth, sorry for not mentioning this more explicitly, but there have been at least three different computer/sound card/monitor setups that this has occurred in, so it's not just one computer or one sound card or one monitor that's the problem.
posted by sleepy pete at 5:59 PM on April 11, 2008

I'm no expert, but maybe it's a ground-loop thing? Some of my buddies w/home studios do a lot of moving things between outlets in order to try to reduce interference. If you can do it without running new outlets or anything, it might be worth a try, anyway.
posted by box at 6:11 PM on April 11, 2008

Well, it's not hopeless (re-reading my answer makes things seem so!). You can do things to help reduce the noise. For one, putting your computer with all of the cables (for the mouse, keyboard, USB, etc) might help a bit -- you'd have to experiment to find something that works.

box - yeah, if there's a ground loop anywhere, it acts as a giant EM coil. Eliminating ground loops can be tricky, but in the case of a guitar plugged into a preamp into a computer, there really isn't one big ground loop. The guitar pickups are small coils that detect vibration of the metal strings, but from there, I don't imagine there's a big loop through the amplification electronics. If you took any introductory univ. level physics, you'll recall that it's magnetic flux determined by the area inside the loop that will grab any induced fields (that is, it's the space defined by the curve, and the flux through that "surface").

If you have direct access to earth ground, you can try connecting those up on your outlets. The closer together the relative grounds are, the better your SNR will be. If you have a cable with poor shielding, a sort of hacky way of adding shielding is to take a regular insulated copper wire (say, 16-20 gauge) and wrap it around the cable through the entire length -- leave one end unconnected and attach the other end to earth or outlet ground. The idea here is that you're creating a ground-return path for the inevitable inductions that the changing currents on the cable generates.
posted by spiderskull at 6:33 PM on April 11, 2008

Whoops, that should read:
For one, putting your computer with all of the cables in a large metal cabinet
posted by spiderskull at 9:52 PM on April 11, 2008

Your guitar pickups are an antenna. When you touch the strings you create a path to ground.
Humbucking pickups were invented to get rid of the problem of single-coil pickups buzzing. Active pickups (in a bass, usually) also remove induced noise.

Once upon a time at a recording studio there was a bass player having problems with buzz when he removed his hands from the strings. Not being able count on him not removing both hands from the bass throughout an entire take, the recording engineer grabbed a wire with alligator clips on both ends and attached one end to the bass player's bridge, the other end to the bass player's nipple ring, thus solving the problem by creating a path to ground that didn't involve the bassist's hands.

...Which worked fine until break time when the bass player put down the bass and walked away without remember the ground wire.
posted by lothar at 10:14 AM on April 12, 2008

I don't think the computer has anything to do with the noise that happens when you let go of the strings. It is a grounding issue. The bridge on a guitar is wired to ground in the electronics of the guitar, so that touching the guitar strings will ground it through your body. You get the same result if you touch the output jack, tuners, metal control plate, or anything else connected in the loop. A properly wired guitar with a star grounding pattern of wiring and good shielding will reduce the noises that it picks up, but even the best guitars can have some issues depending on the location you are in.

One solution is to get those grounding straps that you can use for computer work, attach one end to the guitar either the bridge, output jacks, or something else metal that is wired in to the guitar) and attach the other end to the player. WARNING: if there are any electrical issues, this may not be safe. A faulty guitar amp could send a charge through this connection into the players body. In a recording situation I don't think this will happen, but it pays to be on the safe side.

When I record, I have to turn 90 degrees with my guitar to get the hum to go away. Even with LCD monitors, if I face towards the screen I get a hum, so I face to the side and it goes away. I don't know if this is due to the monitors or something else, but I have had similar situations in almost every home studio I have been in.
posted by markblasco at 10:43 AM on April 12, 2008

A couple quick fixes. 1. ground everything to a real ground, like a water pipe or something.

2. You can get a noise canceler thingy from radio shack that goes inline from your pc to its power strip/surge protector. I forget exactly what its called but it does a good job keeping the computer from feeding signal (zzt) back into the power source.
posted by snsranch at 3:41 PM on April 13, 2008

When I have had ground loop problems from scenarios like the one described here, I use a ground loop isolator like this one found at RadioShack for $17. There are cheaper ones on NewEgg and the like but when you are in a pinch like I was when trying to stream a live performance with a separately grounded laptop and mixer, RadioShack comes to the rescue (All hail to the Tandy Corp. - you know your ass has been saved by them more than once). It is a great feeling to be liberated from the maddening swirl of electromagnetism in the shielding of audio connection cables.

Now the only problem is that these cheap audio transformers introduce distortion. So if you have low tolerance for distortion in your application this might not be acceptable for you.
posted by devehf at 8:05 AM on June 1, 2008