Zoom H4n + MXL 603s = Low Frequency "Bumps"

Discussion in 'Location Recording' started by devguydavid, Dec 6, 2013.

  1. devguydavid

    devguydavid Active Member

    I am just getting into sound and am very much a novice. I recently purchased a Zoom H4n and a pair of MXL 603s. I'm attempting to record a choir I'm in using this gear. I've made some test recordings and have also recorded a rehearsal. In these recordings I'm noticing a low frequency bumping noise. At first I thought it might be the microphones picking up steps, but it happens when there are no steps and only seems to happen in one channel. It also sounds electrical to me and not caused by an external sound source.

    Here are a couple of audio samples that exhibit the behavior in the right channel. has some very rapid "bumps", and has a number of distinct ones.

    I've tried switching cables and microphones, but haven't had enough time to really track it down. Any ideas on how I can debug what's going on here? Does this problem sound familiar to anyone?

    Our performance is tomorrow, so I don't have a lot of hope that I'll be able to get rid of this by then. It does seem that a high pass filter in Audacity takes these out pretty well.

    Thanks in advance for any ideas!
     
  2. Boswell

    Boswell Moderator Distinguished Member

    The waveforms point to it being either a real acoustic effect or else a power supply problem. I'm assuming you were using phantom power set for 48V for the MXL mics. Was the H4N running on batteries or its mains adaptor?

    You could try the low cut filter set to 80Hz or 98Hz during recording. This is described in section 2-03 of the H4N manual.
     
  3. devguydavid

    devguydavid Active Member

    Thanks for your reply. I did have 48V phantom power set. The H4N had batteries in it but I had it plugged in. I assumed it would use AC if plugged in even if there are batteries in it. Maybe I'm wrong in that assumption. I haven't had a whole lot of time to really look at the manual yet.

    I'll have to check out the low cut filter on the H4N. Thank you for the suggestion.

    I tried some recording at home with my piano and didn't hear these anomalies. I recorded a few songs, so would have expected something to show up, which suggests it is something environmental. But maybe there's flakey power at the location? Or maybe there really is some acoustic effect happening. I'm also starting to suspect the H4N; maybe one of the inputs is a little loose or something.
     
  4. JWL

    JWL Active Member

    I think it's acoustic. It could be air moving into the mic. Was one of the mics placed near an air vent or a door or window?
     
  5. lbeasley

    lbeasley Active Member

    Yea, to me this doesn't sound electrical or digital related. Do you have your H4n mounted to a stand or is it laying on a surface? I use to pick up some annoying acoustic vibration noises when laying the H4n on a surface. I then started using rubber absorption/vibration tabs on each corner of the H4n. (The ones typically placed under each corner of studio monitors). This pretty much resolved my vibration acoustic issues when not using a mount. You can also buy custom shock mounts off of amazon for the H4n e.g. Amazon.com: Alzo Shock Multi-Mount for Shotgun Microphones & Audio Recorders- Includes Zoom H4N, Tascam for Dslr And Camcorder Video Recording: Camera & Photo . I have not yet invested in a shock mount, but may do so in the short future.

    As a quick fix attempt, if it's laying on a surface, try placing something rubber under the unit. If it's on a stand, perhaps a rubber mat? Also, you may want to use the wind sponge that came with the device. This really does help with air/wind.
     
  6. Boswell

    Boswell Moderator Distinguished Member

    The OP says he was using external mics.

    His performance is well past (7 Dec 2013), and he hasn't come back to us to say how the recording went.
     
  7. devguydavid

    devguydavid Active Member

    Thanks for the replies and the ideas!

    I never did track down what the problem was. The mics were pretty far from any windows or ventilation, but just in case I used the foam windscreens. (I do think they helped a little, because there was some central heating going during the performance.) The church where we performed has a permanent wood riser stage covered with carpet. I'm now suspecting that a foot tapper was the culprit, along with people walking around during the rehearsal, because I didn't hear these (that I noticed) in the actual performance. We do have one guy who does like to tap his foot from time to time, but it's usually during music. He was pretty far from the mics, but I suppose the taps could have made their way through the floor.

    Thanks again!
     
  8. devguydavid

    devguydavid Active Member

    The H4n was on its own mic stand, and the mics I bought came with shock mounts. I imagine those helped, but I did still hear it.

    BTW, is there a good place to buy those rubber absorption tabs you mentioned? I'll also have to look into that shock mount for the H4n. Great idea!
     

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