Microphones not equally sensitive

tsj9191

New member
Dear Home Recording members,

Total amateur here, worrying about things not being "perfect". Thanks in advance for your attention.

I am breaking into recording acoustic piano for the first time and I am desperate to avoid early mistakes. I have a pair of NT55s currently just within the top of my upright piano. Positioning, sound quality and actual progress aside, I am noticing something strange. Both microphones are set to -10dB and high pass filter off, same gain on the mic pre, everything zeroed on Reaper, and yet, one microphone appears to be picking up more noise than the other. No matter how I swap the mics about, swap the capsules, move the switches around, the same mic is noisy. These were sold as a matched pair, as much as that is worth, so I am assuming that they should respond the same at a basic level.

Annotation 2020-10-15 175731.jpg

When I increase the gain in the quiet mic to the point where they are both picking up the same background noise, the noisy one also appears to have a much longer decay on the levels visible. If that is poor phrasing, the level stays high after the sound is gone for half a second, whereas the quiet mic level drops the instant the sound is gone. The following is a low res screen capture of what the meters get up to when theres noise. The preamp and all other levels are equal for the mics.

streamable.com/fed9t3

I am at a loss. Is this even important? Is one of the microphones faulty? Should I agonise over something else? Any and all advice about what to do next is appreciated.
 
The same mic on both inputs with different cables is noisy? I know you've mentioned swapping things around, but didn't see anything about cables or input channel... not that this helps, but it would eliminate possible problems so you'd at least know it is the mic itself with the issue... only worry about the noisy mic first... plug it into channel 1... swap cables... plug it into channel 2... swap cables... it could be an input issue, a cable issue, or a mic issue... but at least you can take part of the equation out.
 
Thank you for your input, Ujn Hunter. I have the mics set up as a spaced stereo pair, as far as I am aware. Similar to the upper two mics in:

QA_05a-avlFTAOYmKLW3laJ3Om005DETeiz3AxJ.jpg

When I change the places of the mics, without moving any other hardware, the problem switches sides.

I am hoping and praying it is not a hardware issue, so I've been tweaking things like crazy...
 
Why do you need to use the pads? Try with no pad to see if it makes any difference with respect to your problem.
 
Why do you need to use the pads? Try with no pad to see if it makes any difference with respect to your problem.

Thank you RRuskin. From the reading around I have been doing, I was under the impression that close miking a piano often benefited from a mic pad. I will try without tomorrow.
 
Thank you RRuskin. From the reading around I have been doing, I was under the impression that close miking a piano often benefited from a mic pad. I will try without tomorrow.

You only need a pad when either the the incoming signal overloads the mic preamp. I've mic'd grand pianos with mkh series mics, which are extremely sensitive without needing to pad either mic or mic pre.
 
You only need a pad when either the the incoming signal overloads the mic preamp. I've mic'd grand pianos with mkh series mics, which are extremely sensitive without needing to pad either mic or mic pre.

Just to clarify, you need the pad when the mic's internal circuit is overdriven, which can happen with condensers on loud stuff (probably not a piano, but...?).
 
Just to clarify, you need the pad when the mic's internal circuit is overdriven, which can happen with condensers on loud stuff (probably not a piano, but...?).

Agreed but the only time I've ever encountered such a problem it was when I had a lavalier condenser suspended inside a snare drum.
 
Testing thoughts:

1 Switch the pads off.
2 Put the mikes in the same position (i.e. don't worry about your preferred recording positions for the moment).
3 Swap cables to see if the noise is in a cable
4 Swap interface channels to see if noise is in interface.

A quick test to see if it is a mike is to connect one up, get a level from it, then take that mike out and put the other in the same lead. (Mute monitors or headphnes when you do so you don't get a loud click).

If it turns out that one of the mikes is noisy, contact Rode. Their service is very good. It's worth registering your mikes with Rode.
 
If you are having an issue with the matched pair not matching, I would definitely contact Rode. If you registered them when purchased, you probably got a 10 yr warranty. I've never had to use their warranty service, but I have heard that they are pretty good about working to resolve issues.

One other thing that might cause variation is if one was exposed to excessive humidity. You might try putting it in a plastic bag with some silica gel desiccants.
 
When I change the places of the mics, without moving any other hardware, the problem switches sides.

Okay. So either the Mic, Cable or Input Channel is the problem, it's not like you have background noise on one side of the room if switching sides moves the sound with it... I still think you need to take the "bad" Mic and test both cables with that one mic on both channels so you can rule out one of the pieces of equipment as the noisy culprit!
 
I suggest you get systematic about this.
If you haven't already done so, label the mics, e.g. 1 and 2 (paper masking tape leaves no residue) and tape them together.

Now set them up somewhere and set the AI gains to get a reading of the background noise, say about -30dB fs. Adjust the gains to get equal 'blipping' as best you can, even a "matched pair" will show slight differences and the gain/knob positions will not be exactly the same on the AI but I would think things should match to better than 3dB?

Now pull the XLRs out of the AI TOUCHING NOTHING ELSE. I would expect the meter scale to descend off the bottom, certainly below 70dB fs if it goes that low. If one channel IS blipping above the other you have a duff AI but from what has gone before I think it likely you have a faulty microphone.

BTW. It is always a good idea to do such a "Silent" test once a month or so because low level crap can creep into a system and you don't find out until it is too late. As a guide I would expect a good AI to deliver a noise floor better than -80dB with gains set for capacitor mics on speech. On a line input (no input) -100dB fs is easily achieved by quite modest gear these days.

Keep such a recording (24 bits BTW!) for reference.

Dave.
 
I've never done a test once a month on ANYTHING. In fact, in my career, just one mic has actually become faulty - and that was a humidity problem that went away after a warm up and silica gel. I really can't imagine any kind of regular testing regime. Some of my mics won't have even been out of the microphone box for years!
 
I've never done a test once a month on ANYTHING. In fact, in my career, just one mic has actually become faulty - and that was a humidity problem that went away after a warm up and silica gel. I really can't imagine any kind of regular testing regime. Some of my mics won't have even been out of the microphone box for years!

No Rob, not testing the mic! Testing the whole recording setup in terms of noise. Your systems are I am sure totally professional and likely 'set in stone' so the likelyhood of a noise 'gremlin' getting in is very low. Home recordist often have to build up and break down at least part of their setup from time to time or add other pieces of kit. This can lead to noise intrusion.

Dave.
 
Ah, I see - I think? I'm one of those who never ever turn things off and I tend to wander in, turn the light on and just carry on - sometimes things sound 'wrong' and I find and hunt things down, but I just aren't one of those people who tidy up and put away. I think being plugged in and warm is the kindest thing for electronics. 16 years on for an amplifier is my record here.
 
I'm one of those who never ever turn things off and I tend to wander in, turn the light on and just carry on.....I think being plugged in and warm is the kindest thing for electronics. 16 years on for an amplifier is my record here
Ha ha, don't tell that to Greta Thunberg or the guys at Extinction Rebellion !
 
Ha ha, don't tell that to Greta Thunberg or the guys at Extinction Rebellion !

There is that but also Rob, you are lucky you have not had to do a 'hard reset' on digital kit. Also, and I am being a picky, techey old sod here, electrolytic capacitors are only rated for some 10,000 hrs of continuous operation. That they seem MUCH more reliable than that is because MOST peeps give 'em a rest!

Dave.
 
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