Good Mic, Bad Hiss

Hi Steve and everyone. It's been a while since I've posted, but I'm at wit's end and need your help. I have some "white noise" or, a hiss that appears in my voice recordings (Neumann TLM 103). It seems to have appeared after a couple of recent, close together, brief power outages. I have routed the audio in different ways to try to see if the noise is coming from something other than the Neumann, but I get it using a Rode NT1 as well as a Shure SM58. I've tried changing around the audio chain. i.e., I've gone mic>mixer>mic preamp>digital audio interface>PC. I've tried mic>Mic preamp>mixer>D.A.I.>PC to just mic>D.A.I.. It's still there. I have switched mic cords. I have switched mics. While recording, if I unplug the mic's XLR at either end, the recording goes silent (good). If I turn off the Phantom (+48v) it goes silent. If I bring down the mic input, the hiss level will go down. I almost seems that the mic input is super-sensitive, yet my voice wave looks nornal and sounds okay, yet still has that background hiss. It's not a constant rate while recording either, it's wavering 3db up and down several times per second. When I touch the mic boom, the input level spikes abnormally high. Heck, when I touch the mic boom, I can see the Sig/DL lights turn on on the digital interface (TASCAM US-144) I've attached the hiss audio. I'm not sure if a screen shot would help.

This may be a completely stupid suggestion, but are you sure that something hasn't changed in the studio layout or method of operation that is causing people to speak more quietly?

I have had many, many situations where there have been complaints of mixers going noisy and where an investigation has found that someone had moved screens etc., and the contributor had begun to speak more and more quietly.

That is now one of the first things I would check for, as just winding the wick up would explain how hitting the mic stand would sound louder and the hiss would appear to have appeared (if you see what I mean).

Thanks for responding. This studio is my home studio, so the only talent is me. After checking various cables and configurations to try to narrow down the problem, I have started again with all inputs at zero. Then, while watching the wave form recording in Adobe Audition, I spoke into the mic, first increasing the input gain on the mic channel until I reached zero on the VU. Then I turned up the gain on the mic preamp until VU's were at a good level and I turned up the Left and right sides of the digital interface and now I can see the noise recording. I unplug the mic from the mixer and the noise doesn't show in the recording. I plug in the mic cord, the noise level returns. I turn off the +48v and the noise drops, now when I turn phantom back on, it's clean for about 3-4 seconds and the noise fades back in. (I think that's a normal time lapse for the +48v to activate). It almost sounds like it has something to do with grounding in the electrical has changed. So, my next step is to unplug everything and reroute electrical and audio to separate them as much as possible. By the way, I went directly from the mic into the digital interface, bypassing the mixer and mic preamp. The DI has it's own +48v switch and when I turned it on, the noise was in it. I'm not a radio engineer, just a PD, and I am at wit's end, what little wit I have.

I'm going to lower my mic gain and amplify the voice in post production. It'll work okay when I apply noise reduction, then amplify. I don't know what changed with my setup, but I'm not dead in the water.

Have you inadvertently moved the pad switch on the mic? Have you tried a different cable?

Have you tried using only the mic and mixer while listening to the output of the mixer through headphones?

Is the humidity high where you are?

James.

Since the noise comes and goes with the phantom power, it seems most likely that the phantom power supply itself or one of the balancing resistors is the culprit. To verify that, you should exchange the preamp (or the mixer if the preamp is included). You might also try to measure the 48 V on both side of the XLR plug. Take care as shorting to ground may damage the balancing resistor.