Home recording studio questions

January 1, 2004 1:34 PM

Home recording studio questions: (1) What to do about sound source with a noise problem (sounds like a bad ground loop) and (2) building some approximation of an isolation booth. [more inside]

(1) I've got a Chet Atkins Electric Classical and a Hughes & Kettner amp combo that I like quite a bit. There's a low hum that gives me pause when recording, though, and it's especially bad if I use the XLR direct out on the back of the thing. I could mic the amp cabinet, but I'm a little bit afraid to do that because the walls/ceiling are sortof thin where I live and there's lots of ambient noise. I'm pretty sure the amp is the problem, as I don't get the noise if I just take the guitar straight into an M-Audio pre-amp (which is probably an audio atrocity, but it works). I thought of trying to record the hum and inverting it and trying to keep that synced with the actual track, figuring superposition would mean I'd get reduced noice. I have not tried a narrow notch filter yet.

(2) So the other things I could do is build some kind of isolation booth. I can't really modify the place, so it has to be freestanding and I don't have a lot of room anyway, so it has to be something I can set up and take down and store without too much trouble. My first thought was a PVC pipe frame around which I could hang some quilts. Any others?

posted by weston to Technology (6 answers total)

since no-one has answered... have you tried usenet? i don't know about guitar, but for bass, alt.guitar.bass would have (at least, a few years ago) been the first place to go if you were recording a bass (imho). you might try alt.guitar.amps (google has an interface to usenet - just select the "groups" tab of go here.) with a bit of luck someone might say "oh, that's a common problem with that amp, you just need to ..."

incidentally, i think you're mixing bad grounding with ground loops. your amp might be badly grounded (causing the hum), or you might have a problem with ground loops between amp and whatever you're using to record (but afaik ground loops sounds squealy, rather than hummy). anyway, if it is a ground loop and you're using separate sockets (on different sides of the room), try plugging everything into the same block of sockets.

oh, and is there any such thing as "an audio atrocity" if that's the sound you choose to make?
posted by andrew cooke at 3:12 PM on January 1, 2004

Having you tried moving the guitar and/or the amp around to see if the hum lessens? Also, turn off any dimmer-controlled lights — the rheostats are terrible electromagnetic noise generators.
posted by timeistight at 3:33 PM on January 1, 2004

If you're recording at home, I understand that a ground loop is almost unavoidable - home electrical systems just aren't made to isolate power sources. If you're going to record through the amp, you might as well mic it in an isolation booth rather than take a line out - I've always hated the sound of DI guitars, because real speakers provide a necessary high-cut filter on the sound.

In my experience, though I think the 60hz notch filter would be a good start - if you're recording digitally or can import the recording into Cool Edit, some of the filters on there are very powerful. They aren't plain old FFTs, they can narrow down to a tiny slice of the audio spectrum and remove it seamlessly.
posted by Jimbob at 3:39 PM on January 1, 2004

first up, mic'ing the cabinet is definitely the way to go. anything else sounds terrible. but as far as the hum does, does it remain constant whether there's an instrument plugged in or not? also remember that hollowbodies feedback a little naturally.

if push comes to shove, maybe you can try putting this noise reduction plug-in on your recordings. I've used it for years and it works awesomely. the price is steep but if you're resourceful AHEM you might be able to get a copy for free off of "the internet."
posted by mcsweetie at 10:57 PM on January 1, 2004

make sure you have a few seconds of silence (except for the hum, which you obviously can't get rid of) in the beginning/end of your recording. save to wav and open in cooledit. use the cooledit noise reduction filter by selecting a couple of seconds of the silence in the beginning of your file, then analyzing that in the filter, then select the whole file, and hit OK on the filter... it will then remove those humming frequencing from your entire recording, leaving everything else essentially intact. this is basically the same thing as noise reduction VSTs, but cheap/free.
posted by edlundart at 2:46 PM on January 2, 2004

for the 2nd part of your question, you may find this article useful.
posted by edlundart at 2:50 PM on January 2, 2004