Can you diagnose what's causing this sound?

omnikron

omnikron

Well-known member
I'm having a strange sound problem I can't seem to get to the bottom of. It's coming from a Motu Traveler (mk1). I've tried running it from firewire bus power, d/c power through the wall, I've tried different inputs, and the problem is still there.

Below is the link for 2 sound files. You will hear the sound as a fluctuating mid-pitch sound. It's this dirty noise.

https://drive.google.com/folderview?id=0B2WGNi0VngXPN3g1aExYYkNZRk0&usp=sharing

The problem only happens with the following mics:

Sennheiser MD441-U
Sennheiser ME66 w/ K6
Schoeps CMC5 MK41

The problem does not happen on the following mics:
Audio Technica 4073a
Electrovoice RE-20

I have a Motu 896mk3 that I've also tested and the problem does not exist on any of the mics with that audio interface.

Does anybody have any idea what's causing this?
 
Sorry, your files will not open. In Sound Forge Pro which normally opens any audio file type.
Re-render/post it in a uncompressed PCM (WAVE or AIFF) format.
 
That's strange. It's a .aif file that plays fine for me even from within the Mac OS (quicktime player) preview.
 
It's likely a Apple Lossless AIFC file which uses the <.aif> extension. Let me try it in my audio PC later on, maybe my laptop's codecs are not up to date. It plays back in the VLC player but I'd like to examine the waveform and other SF's analysis tools.
Strange though, Phantom Pwr and non-Phantom Pwr mics. The 441 is a dynamic.. is the K6 on running on battery or Phantom Pwr. ?
 
They opened fine on my OLD Mac so?

What this is 99% certain, is digital clock noise. It sounds like a very faint "modem". Why it's showing up on some but not others??? If it were only the condensers I would think they were just more sensitive but with the mix you list? Could be that the older MOTU box is putting out a bunch of RF and the shielding on those mics is not as good? Were you using the same cable on each? Could be dirty contacts with the capsule or the XLR pins.

I would try swapping out cables and also orienting the mics differently and maybe getting some distance between the mic and the box to see if any make a difference.

Some mics are more RF susceptible and some seem to be sensitive to different kinds of RF. I have a mic that is fine most of the time but picks up naval radar and the underground antennas used to send signals to subs while submerged. It was like this new out of the box and nobody has ever found a "cure", I just know where not to use it.
 
Rick, yes that's exactly what it is. I exported it from Adobe Audition.

After doing some research around on other forums, I have a suspicion it's related to mics not receiving a full 48volts of phantom power, but perhaps a few volts under the specs they need. The Schoeps and Oktava have a more narrow range of voltage they can take. I just purchased a behringer Micropower PS400 and should receive it Monday. If that solves the zzzZZZzz noise I'm hearing, then great. Maybe when I find time and money, I'll replace the unit with a newer mk3 unit but this could be a good $25 workaround as I mostly only use 1 input channel.
 
I just wanted to update everyone here and let you know that the Behringer Micropower PS400 completely resolved my problem. I believe the phantom power circuit on the Motu Traveler wasn't outputting the correct voltage for the mics that were exhibiting a strange ZZzzzzZ noise floor. The mcis that did work had a more tolerant phantom power voltage range they could accept.
 
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