Mid Side Decoding - Volume

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aaronmcoleman

aaronmcoleman

The truth is out there!
I was just playing around with some micing methods for acoustic guitar and wanted some help with Mid/Side decoding.

I used an NTK for the mid, and a FatHead for the side. The NTK was aimed directly at the 12th fret, and the FatHead was aimed at 90 degrees.

In Reaper I copied the FatHead and panned one hard right and one hard left and inverted the phase on the right. With the NTK muted, and both Left and Right faders set to 0 the volume was even on the right and left sides. As I brought the NTK up, the volume on the phase inverted side got way higher. I know this has something to do with the phase cancellation.

Basically in decoding the mid side, I had to lower the phase inverted side a lot (a whole lot, like 10db) to get both left and right at the same volume. I think it sounds good, but is this the way M/S recording works?
 
Nope. That's not how M-S should work. All I can guess is that it must be something in the positioning--perhaps you've somehow managed to get your mid and right mics exactly in phase at certain frequencies, causing gain rather than cancellation. With two relatively large mics, it must have been difficult to get them close enough together. Only a guess, mind you--I've never heard an effect like that.
 
I have had that happen occasionally,even using the exact same mic combination but with different sessions.
I have some theories as to why it happens , but have never had the time to prove it out.
But it is along the lines of your suggested mode of thought about frequency cancellation / boost.
More often than not the closer I get with the mic combo to the instrument, the more I have this issue...particularly if I have the positive lobe of the figure 8 pointed at the bass end / bridge of the guitar...probably because I get added low frequecy reflections from the body directly into the side mic because of the close proximity rather than just picking up more room and open space.

low frequencies being more omnidirectional in nature tend to overcome even the best figure 8 nulls when placed really close.

I have also had the problem with putting the positive lobe too close to a reflective surface.

Obviously there are "fixes" like slightly panning the center track to offset the shift, but I'm sure you want to get it right up front.
 
Yeah NTK is centered. As I bring it up, the volume difference becomes exaggerated.

After doing some reading, it seems like this happens when the mics are less than 24" away from the source. I'm going to play with it today and move back to see what happens. But I like the sound even though I have to lower te phase cancelled side. So I think I'll roll with it for now even if it is "wrong" and keep experimenting.

Thanks. Any technical explanation and recommendations would be cool too.
 
aaronmcoleman said:
I was just playing around with some micing methods for acoustic guitar and wanted some help with Mid/Side decoding.

I used an NTK for the mid, and a FatHead for the side. The NTK was aimed directly at the 12th fret, and the FatHead was aimed at 90 degrees.

In Reaper I copied the FatHead and panned one hard right and one hard left and inverted the phase on the right. With the NTK muted, and both Left and Right faders set to 0 the volume was even on the right and left sides. As I brought the NTK up, the volume on the phase inverted side got way higher. I know this has something to do with the phase cancellation.

Basically in decoding the mid side, I had to lower the phase inverted side a lot (a whole lot, like 10db) to get both left and right at the same volume. I think it sounds good, but is this the way M/S recording works?
Click to expand...

If you put your nose up to the 12th fret of the guitar, does the sound mostly come from one side of your head? A M-S mic setup will do the exact same thing. If the wrong side of the stereo image is loud then either flip the mid mic polarity or both the side mic polarities. (The correct term is polarity, not phase, no matter how many times it's wrong on a switch or in a manual.)

Start with the NTK up and slowly bring in the FatHead channels until you get a little stereo spread. Then fiddle with levels and panning to make it sound good.
 
bouldersoundguy said:
If you put your nose up to the 12th fret of the guitar, does the sound mostly come from one side of your head? A M-S mic setup will do the exact same thing. If the wrong side of the stereo image is loud then either flip the mid mic polarity or both the side mic polarities. (The correct term is polarity, not phase, no matter how many times it's wrong on a switch or in a manual.)

Start with the NTK up and slowly bring in the FatHead channels until you get a little stereo spread. Then fiddle with levels and panning to make it sound good.
Click to expand...

Thanks. That's pretty much what I did, but I was just wondering why the volume was so drastically different in my two side tracks. I'll play with it some more and see what I can get and if I can get it right.
 
When I put my nose on the 12th fret my strings are muted.
 
aaronmcoleman said:
Thanks. That's pretty much what I did, but I was just wondering why the volume was so drastically different in my two side tracks. I'll play with it some more and see what I can get and if I can get it right.
Click to expand...

Technically it is right. If you put your head where the mic array was most of the sound you hear will come from the left (for a right handed player). But it doesn't have to be technically right, it just has to sound good, so do whatever gets it right and don't worry too much about it.
 
Haha. I did a classical piece once where you use your nose on the fifth fret harmonic while the left hand stretches from 7th fret up. It was just the novelty of it though.

I guess I couldn't close mic that piece or my big head would get in the way.
 
bouldersoundguy said:
Technically it is right. If you put your head where the mic array was most of the sound you hear will come from the left (for a right handed player). But it doesn't have to be technically right, it just has to sound good, so do whatever gets it right and don't worry too much about it.
Click to expand...

thanks. What sounds right is, even when it's not. I just want to learn so I'll keep messing with it, and since I like the sound now I'll go with it.
 
Ok, problem solved. I was 12" away the first time and the volume was weird. I moved back 36" and didn't like the overall sound, so I moved closer. It turns out I was too close to begin with, anything closer than 24" caused problems. From 24" back it worked perfectly.

As always, thanks for the help!
 
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