How do you boost the sensitivity of one mic for two-channel sim recording?

  • Thread starter Thread starter Telamon
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Telamon

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Hello forum members:

I am wondering if you know of a way to boost the sensitivity of one mic to balance out the high-sensitivity of the other mic.

Here's what I'm doing:

Recording two tracks simultaneously (acoustic guitar and vocal) through a Focusrite Saffire 6 interface. The mics are a Blue Bluebird for vocals and a Sennheiser e 614 for instrument. The problem is I hardly have to turn up the Blue's channel to get a strong signal, but I have to crank the Sennheiser's channel to match it, and that introduces too much background static. I've turned down the Blue's channel to better accommodate the Sennheiser, but it isn't quite enough.

Does anyone know of a way to boost the signal of the Sennheiser channel without introducing more signal noise?

Specs:

Blue Bluebird
Sensitivity~27 mV/Pa at 1kHz
Noise~7 dBa

Sennheiser e614
Sensitivity~3 mV/Pa
Noise~24 dBa
 
The Sennheiser e614 is a condenser mic, so I'm assuming you have phantom power turned on?

What levels are you shooting for?
 
Both are condensers and the phantom power is turned on to operate both. Both channels have output knobs that go from 0-10. The Bluebird channel would basically have to be on 2/10 to have a comparable level of the Sennheiser on 7/10. Turn the Sennheiser channel past 7 and white noise becomes audible. Turn it up past 8 and it's distracting.

I tried connecting an additional preamp/DI box on the channel, but that created even more noise.

Eventually, I bought another large diaphragm condenser with a comparable sensitivity to the Bluebird as a workaround, but it would be nice to be able to use the Sennheiser along with one of the other mics.
 
I don't know anything more about your setup than the equipment you're using, but perhaps the Sennheiser mic simply requires more clean gain than the Sapphire provides. Could be any number of other issues (the mic is somehow damaged, you're placing it too far away, etc.) But it seems like the clean gain is probably the problem. What was the other preamp you tried with it?
 
Nothing fancy with the additional preamp; it was a Behringer Mic200, I think. I wanted to try a proof-of-concept. I think you're right about the clean gain. The mic doesn't seem broken, but it's possible. I placed the mic about six inches from the 12th fret on the acoustic and was doing travis picking. Any way to boost the clean gain with something like an additional preamp, or maybe just upgrade to a different interface? How is interface preamp volume level measured?
 
Just to throw this into the equation....

What levels are you going for? It could be that you're trying to record too hot, and the solution would be to simply turn down the gain on the other mic.

You should be peaking at around -12 to-6db, as opposed to trying to get the levels as close to 0db as you can.

Like I said, just throwing that in there. You very well might be doing everything right.
 
Rami hit the nail on the head. Avoid getting levels anywhere near 0dB for each mic signal and keep the levels in the -12 area. I struggle with recording vocal and acoustic guitar at the same time in the sense that there always seems to be a disconnect in terms of balance when monitoring with headphones what it is I'm recording. You can deal with balancing post recording provided you didn't clip when recording. Is also helps to run a seperate mixer and headphone amp to balance what you hear in the phones.
 
Just to add to what Rami said, you could even hit peaks as low as -24 and probably be fine.

So, For the most sensitive mic, leave the preamp at 0, and turn the less sensitive mic up.
 
Thank you, RAMI. I see what you're saying and believe it's a good approach. The levels I was going for could've been too hot to begin with, and I've had some troubles with clipping after adding a bit of compression and the mastering plug-ins. That might solve both problems. I appreciate everyone's help on this thread. Thanks!
 
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