Need good ears to tell me if my mic is "broken"
 

Hey all,

I'm using a Rode NTG2 on a Sony Z1. I do lots of events with it.

This year, I started working with a new producer whose events are much louder than I've had in the past. I'm hearing distortion in my ambient audio even with seemingly correct levels, especially in the bass.

Not being an audio guy, I can't tell if:

a) it's a coincidence and it's actually my mic that's gone bad
b) the camera or mic can't handle the sound pressure levels
c) I think my levels are correct, but they're actually too hot. Should I make sure to stay below -20db in loud settings (though I tried this at one of the louder events, and it didn't seem to help much)?
d) some other problem or setting that a bonehead like me can't figure out correctly

Since my trouble started, I've enabled the bass cut switch on the mic, and put a -6db trim on the channel in the input settings of the camera. Wind setting is "on" for the channel (which mostly cuts bass as well, I'm guessing).

One channel I usually leave on auto, the other manual. I've attached two 30 sec samples, which are the same section with the channels separated so that you can hear each on its own.

Are these samples distorted? The DJ's voice seems okay to me, but I hear bad reproduction in the bass. I can't tell if that's just bad reproduction of the bass, or distortion.

Any help, feedback, suggestions would be most useful. Perhaps you can suggest a different mic for loud events that would be a better choice. I don't want to use the internal mic because on this camera, you can't put one channel auto, the other manual.

Thanks a million.

You are overloading the mic preamp in the camera.

Hi Brooks,

Okay. How do I avoid this? Is the trim setting on the camera what I change to fix it? Right now it's at -6db. Or does this setting happen too late in the chain?

I'm guessing setting the levels happens too late?

Or do I need a less sensitive mic?

Thanks.

Oh, I forgot to ask.

Is the trim setting in the Z1 the same as mic ATT in other devices? I've Googled around a bit, but there seems to be no definitive info on it, and the manual says "you can select the level of input signal".

Sounds like that should take care of the problem if I'm understanding the idea of input trim. Does this reduce the signal BEFORE reaching the preamp, thus fixing my problem?

If you have settings in the menu for mic attenuation, use that.
Generally, the trim on camera is after the preamp, so no matter how much you turn it down, it's still overloading the cam mic preamp.
You should use a 10-15dB inline mic pad between the mic and cam, one that passes Phantom power, or use battery instead.

Thanks for your time and help, Brooks. Looks like I'm in the market for an attenuator!

Sure wish there was a way to find out which way it is on this camera. Can't track down any info. Sigh....

Well, I think you might be overloading the mic in the first place. In my experience the NTG2 is very sensitive to bass overload... I would try a different mic probably with a pad like the AKG 300 with the hyper capsule.

Well, darnit! How do I know which one it is? The mic or the preamp? Too bad I don't have an extra $300 mic just lying around for testing purposes....

Thanks, guys.

I would get the attenuator to begin with, it's not very expensive and it's a valuable accessory that you should have anyway.
A switchable model from either Audio-Technica, Shure or a vendor like Markertek will give you some choices of level. Then you can experiment with combos of the attenuator and the camera trim and see what settings work best.
If it is your mic distorting, then there are other choices. The AKG mic mentioned is a great mic, there are others that are less expensive too. The key is buying functional long-term items that you will use for many years and there are many mics that can fit that description that are worth the investment.

Sounds reasonable.

Do you have other suggestions other than the AKG? Or if I wanted to research it on my own, is there a particular type of mic that one uses in loud environments?

Thanks again.

Although my first thoughts were overload of the mic pre-amp due to high level - which a pad between mic and camera would make no difference, after looking at the spec of the mic, max SPL is quoted as 131dB - this is going some, and I suspect if it had been that loud, your ears would have been hurting too! So I'd try the in-line pad.

The key understanding here, I think, is about acoustic energy.

Everyone has stood in front of the big speakers at a concert. You can literally FEEL the air move. This is because low frequencies require a LONG movement of a large diaphram to move the air. At a concert, those low frequencies are typically generated by a separate powerful amplifier and speaker (sub woofer)

So here comes this LONG wave of energy at a very low frequency but with a LOT of power behind it - and it hits the relatively tiny diaphragm of your Rhode and it's a little like pouring a bucket of water onto a water glass. Temporary OVERLOAD.

Particularly if that mic was designed to be sensitive. It has NO chance to respond properly. It's simply overwhelmed.

The other issue is that while that mic is trying to handle the HUGE pressure of the bass, you're simultaneously asking it to get the DJ voice captured clearly. A source in a totally different part of the audio spectrum.

So you need to start with a mic that can handle loud, LOW sounds well. A good choice might be a large diaphragm DYNAMIC like the Sennheiser MD-421U or other traditional "kick drum" mics (there's that high energy low frequency stuff again!)

But while that could be expected to do well with the super bass evironment, it still might not be able to be particularly sensitive to the DJ's voice while it's under attack from the THUMP.

So I'd mic the band to one track, grab the DJ's mic directly to another track with a channel insert off the mixer - and mix the two in post.

As always, audio is complicated.

Good luck.


BTW, don't get confused by the max SPL rating of the mic. That just tells you how much sound pressure it can tolerate before damage occurs. NOT how much SPL at a particular frequency can be ACCURATELY reproduced.

Hi Bill,

I'd love to be able to do that, but options to do this at events are very limited. The few times I've tried it, I get variations between "no, I don't want you to plug into my board" to "sure, it's this output...I think. No, this one....wait...".

I'm no wizard, but I'm continually amazed at how little DJs know about their equipment (though perhaps my questions here say the same thing about me!). I think in my market many of them are hired to use someone else's equipment, so they don't know the ins and outs of it.

I'm thinking of getting a standalone recorder to record the ambient sound of the room. Something like the zoom H2 that won't make me cry if someone steals it, hehe... And I could plug into the board when allowed.

Tell me about it. Video is way easier.

Thanks for your help.

I am continually amazed that many working A/V people do not understated the difference between 'mic and 'line' level.

My 02 cents.

Okay, in another thread another poster suggested:

"Vito, you can tell pretty easily by looking at the waveform on your timeline. If it is clipped ---filled with wave from top to bottom --- you're overloaded. If turning down the trim on the camera gives the same waveform, just at a lower level but still filled top to bottom, your trimmers are post-preamp."

So I stuck my mic in front of my speaker at home and cranked a song into it. Attached is a sound sample and the waveform. Since the the waveform is not flat at -18db trim, does this mean my trim is pre-preamp?

From listening, however, the trim doesn't seem to be helping, so I'm guessing the mic is overloading.