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gain staging when recording one instrument with 2 microphones.
Old 14th August 2019
  #1
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gain staging when recording one instrument with 2 microphones.

I am recording an acoustic guitar in stereo using XY technique and have a question regarding gain staging. One of the microphones is at the 12th fret pointing at the headstock while the other one is at the 12th fret pointing at the soundhole. The signals have very different SPL. Should I match the volume on my preamp so they have roughly the same volume in my DAW? If so, why? Or if not then what happens if I pan them hard left and right? one side will be much louder than the other. Is this a problem?

thanks a lot!
Old 17th August 2019
  #2
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akebrake's Avatar
 

Treat like a pair

Quote:
Originally Posted by camomiletea View Post
... The signals have very different SPL.
Yes, largely because of the instrument itself if mikes are close.

An acustic guitar have an ”uneven polar pattern” with more SPL (lows) at the Sound Hole & Sound Board.

In the pic the Red X/Y (Cardioid) mic is pointing towards the Sound Hole. (more SPL more lows)
The Green towards the Head stock. (Less SPL /but more highs)
The Center of the ”stereo image” is in front of the 12:th fret with equal gain on the mic pre.

gain staging when recording one instrument with 2 microphones.-xy-rec1.jpg

Quote:
Should I match the volume on my preamp so they have roughly the same volume in my DAW? If so, why?
Yes, IF the stereo pair are ment to ”hear” the whole room as a wide stereo image (between your monitor speakers) with the guitar somewhere in the middle. Same preamp gain.

Pre amp gain also adjusts the L/R "noise balance". Room noise, mic noise, pre amp noise) Quite appearing if you listen in head phones.
Guitar/room ratio depends on the mic distance.

With different gain the whole stereo-image will tip to one side.
(Like the balance control on your ”stereo”)

We like a clean (low distortion) recording with good signal to noise ratio.
Like every recording (including REW sweeps).

X/Y (Coincident) stereo-mic technique relies mainly on level differences between L& R. Gives a more pin-point /detailed image
(A/B stereo) Spaced microhone pairs also have a time difference. Gives more spacious result with less details.

What’s the intent of the recording?

Is it a trubadour, rock song, ballad etc. together with other instruments or just a solo classical guitar concert?

Tip:
Try moving the mics further away from the guitar and get less proximity (and more room) If room noise permits...

How is your Isolation? Traffic, neighbors, Rain, AC? Refrigerator, fans...
Is your room live and ”good sounding” for acoustic instruments? Or more dead?

Hope that helps
Attached Thumbnails
gain staging when recording one instrument with 2 microphones.-xy-rec1.jpg  
Old 18th August 2019
  #3
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Quote:
Originally Posted by akebrake View Post
Yes, IF the stereo pair are ment to ”hear” the whole room as a wide stereo image (between your monitor speakers) with the guitar somewhere in the middle. Same preamp gain.
THanks for your post. It is a good one.

So in the OP I actually never meant having the same preamp gain. I meant to bring up the gain of the "green" microphone so that the recorded level is similar to the "red microphone? in my DAW. If I did use the same preamp gain, the level on one mic would be much softer because the recording comes out much softer when pointing at the headstock. Maybe this is the point and it is supposed to be that way for it to be realistic sounding, I don't know. So the reason I was asking about this is because it sounds a bit lopsided if you know what I mean? Do engineers normally use the same preamp gain on both XY mic's or is it common to use a much higher preamp gain to get a similar level for both microphones?

Quote:
Originally Posted by akebrake View Post
What’s the intent of the recording?
I was just experimenting because I wanted to see if it was possible to get a more balanced acoustic guitar sound from two microphones. I wanted to perhaps use the 0 - 500Hz frequency from one microphone and then the rest from another microphone. Is this even possible? Or does it cause phase issues if I use a HPF on one microphone and a LPF on the other and combine the signals? The reason is that in some mic positions the low end sounds better and more balanced and in another position the mid range sounds a bit better and balanced.

To answer your question, I have a lot of bass trapping in my room around 50cm of low density fiberglass all around with wooden slats covering around 50% of the wall surfaces and some diffusers here and there but in my opinion, the room sounds more dry than anything else. The wooden slats are about 1cm thick so I am sure they bring back some high (or maybe mid range too but not sure about how much 1cm thick wooden slats will change the frequency response of the room, I should test this one day) even though to my ears i tis not audible

Quote:
Try moving the mics further away from the guitar and get less proximity (and more room) If room noise permits
Absolutely, I don't like microphones too close to the guitar. I go for around 50cm away pointing at the upper bout at 45 degrees from the 12th fret. This is the most balanced position IMO. Anything closer than that and the low end gets too much boom. I have a Martin D28 which is like the mother of all dreadnoughts . In an untreated room I think this would be too far away but in my room it sounds best.
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