3:1 rule for stero mic'ing a guitar

  • Thread starter Thread starter trion12
  • Start date Start date
T

trion12

New member
Hi,
I understand that this rule states that when stereo mic'ing a guitar that the distance between the 2 mics must be at least 3 times the distance of each mic from the guitar.
Being that I want to record with one mic pointing at the 12th fret and another pointing at the bridge, and that the 12 fret and bridge are 14" apart, that means that the mics must be less than 5" from the guitar.

This causes me 2 concerns.
First is that it is a little closer than I would like from a comfort point of view.
Second, I understand that I will get more room sound if I back the mics away from the guitar further but then I will be violating the 3:1 rule and risk phase issues.
What's the solution to having the mics a more comfortable distance away without getting phase issues?
Is the answer to spread the mics further apart but to angle them towards the 12 fret and bridge? if I do this am I not likely to get a more boomy sound as the mics will be pointed more directly towards the soundhole?

Thanks,

Aaron
 
The 3:1 rule applies to multiple-mic'ing of a sound source, not stereo mic'ing. Stereo mic'ing requires specific mic placement techniques that with the exception of "spaced-pair" placement, do not follow the 3:1 rule...

As Sloan said - the best course is to use your ears, and adjust mic placement as needed to balance tonal characteristics and phase cohesion.
 
Also, the 3 to 1 rule applies to distance from the source. If you needed to use it, the 3rd mic would need to be 3 times the distance from the guitar that the other mics are from the guitar. Not how far they are apart.
 
Just to nip this in the bud from a slightly different angle than the good prior advice above.. :D
trion12 said:
Hi,
I understand that this rule states that when stereo mic'ing a guitar that the distance between the 2 mics must be at least 3 times the distance of each mic from the guitar.
Click to expand...
...No. That is the approximate guide for when you don't want to hear the effect of the second mic. And, even then it only works for that purpose if the two are at similar volumes. As soon as you bring the 'other one' up again in the blend, it's back to null and void time. :p
3:1 fixes a volume problem. It has nothing to do with fixing where it phases'.
Wayne
 
Last edited:
mixsit said:
3:1 fixes a volume problem. It has nothing to do with fixing where it phases'.
Wayne
Click to expand...
I was under the impression that the 3 to 1 rule prevented a phase cancellation problem of some frequencies combining out of phase. How does it correct a volume problem?
 
The application is to reduce combing if you have two mics on two different 'voices, by keeping the signal (voice/source) to noise (bleed and nulls from the other) ratio up, by attenuation from relative distance difference.
Relative distance determines which frequencies will null/boost, relative volume/sensitivity determines how deep the nulls/boosts will be.
Think time=frequiencies Vs volume=depth of the phase.
:)
 
The 3 to 1 idea as I've heard it best described, applies usually to mic'ing different sources where the mic's will be combined to a single channel. The purpose of the rule is to reduce mic bleed/phase problems. Distance also depends greatly on the pattern of the mic's. Hypercardioids can be closer than wide card or, especially, omni.

So if you're doing stereo mic'ing in XY, ORTF, NOS, etc., it's not applicable.

If you're using 2 mic's on a guitar in a non-stereo config, like at the 14th fret and bridge, your approach might depend on whether or not you're going to pan hard L and R, or collapse the image some.

It's true that the only real rule is to trust your ear.

Tim
 
Thanks all for responses, but I have to admit I am still confused.
I am looking at 2 mic's - one pointed at the 12th fret and one pointed at the bridge, with each mic an equal distance from the guitar (between 8-12 inches)
They will be panned hard left and right in the mix.
I have experimented with a variety of configurations (X-Y, ORTF, etc . . .) and this is the one I like best for solo acoustic guitar.
Is the general consensus that I can ignore the 3:1 rule with this mic configuration?
I was under the impression that this rule was to ensure there is no phase canceleation when the recording is played on a mono device.

Aaron
 
trion12 said:
...I am looking at 2 mic's - one pointed at the 12th fret and one pointed at the bridge, with each mic an equal distance from the guitar (between 8-12 inches)
Click to expand...
So in that case they are both seeing about the same time delay to the guitar, with maybe some nice lower level phase effects in what ever differences might strike each of them from either sides of the guitar, or the room. (This is nothing more than a WAG* on my part here. :)
So how's it sond? :D
Wayne







*WildAssedGuess
 
Now I am even more confused.. These pages says that IS an issue when stereo mic'ing a guitar in a space pair configuration.
Click to expand...

Yeah, I've seen those pages. IMHO they're misusing the term, but hey, to each his own. As a stereo mic technique, a spaced pair is not meant to be mono compatible. XY or Mid/Side are though.

On the practical side, I think the best quality of spaced pair mic'ing up close on guitar is the larger than life sound you get with the mic's widely panned. It's not a technique I'd use if I was going to sum the mic's to mono. Playback on a mono clock radio probably won't sound as good as if it had been recorded in XY. But on a nice stereo it'll sound like a 10 ft wide guitar.

What do the rest of you guys think?

Tim
 
Timothy Lawler said:
On the practical side, I think the best quality of spaced pair mic'ing up close on guitar is the larger than life sound you get with the mic's widely panned. It's not a technique I'd use if I was going to sum the mic's to mono. Playback on a mono clock radio probably won't sound as good as if it had been recorded in XY. But on a nice stereo it'll sound like a 10 ft wide guitar.
Tim
Click to expand...
Tim,
My reason for starting this thread is beacause I love the wide sound image of a spaced pair on solo acoustic guitar.
While ideally the stuff will get listened to on a decent stereo, I am also chasing radio play and the output there will be AM radio.
Hence my concerns.
Aaron
 
While ideally the stuff will get listened to on a decent stereo, I am also chasing radio play and the output there will be AM radio.
Hence my concerns.
Click to expand...

Yeah, I hear you. It's a dilemma. If your main objective with a recording is AM radio, you might consider XY with a wide reverb to fill it out more for stereo listeners, as long as the reverb is one that doesn't tend to phase itself out in mono. Or just go for the 12th fret/bridge placement and finely adjust the mic's when tracking to minimize phase problems in mono (maybe monitor w/headphones in mono as you play).

I did a CD that's had airplay on classical radio, and recorded it with the 12th fret/bridge spaced pair method at about 2 ft distance. I've been told that some FM stations have signal processing that, although stereo, can cause problems with comb filtering if the tracks aren't mono compatible. Ended up just by luck that it didn't have any noticeable phase problems in mono anyway. One of the tracks is here if you want to hear it. But if I was aiming at AM radio, I'd use XY myself.

Tim
 
In all or most of those multi-mic examples note that each pair is at equal distance from the source, and generally on either side of the main center, the body or sound hole. There is not much cross/time pahsing going on from that direction. On spaced pairs, or NOS or ORTIF, if you pull the pair back (equally) it begins to blow the 3:1' out, the stereo image gets narrower (smaller on the sound stage) but still slips into a set of valid stereo distance mic techniques with similar 'pleasing' and (sometimes appropriate?) phase effects.
Just to point out how time' might be more powerful the 3:1, try 1st mic at 1", 2nd mic at 9", 12th fret and bridge, equal stereo volume. That's 9:1... :D
Again, for my part, this is seat of the pants driving here. ;)
 
Timothy Lawler said:
Yeah, I hear you. It's a dilemma. If your main objective with a recording is AM radio, you might consider XY with a wide reverb to fill it out more for stereo listeners, as long as the reverb is one that doesn't tend to phase itself out in mono. Or just go for the 12th fret/bridge placement and finely adjust the mic's when tracking to minimize phase problems in mono (maybe monitor w/headphones in mono as you play).

I did a CD that's had airplay on classical radio, and recorded it with the 12th fret/bridge spaced pair method at about 2 ft distance. I've been told that some FM stations have signal processing that, although stereo, can cause problems with comb filtering if the tracks aren't mono compatible. Ended up just by luck that it didn't have any noticeable phase problems in mono anyway. One of the tracks is here if you want to hear it. But if I was aiming at AM radio, I'd use XY myself.
Tim
Click to expand...
Tim,
I won't say that AM radio play is the main objective, but it is a significant marketing channel (public radio).
The other option I suppose is to record in stereo with a spaced pair as planned but perhaps cut some mono CDs for distribution to AM radio using only one channel . . .
BTW Nice tune and nice playing. You get a nice tone from your right hand.

Aaron
 
Timothy Lawler said:
Aaron,
How are your recordings now as far as mono compatibility? Are you hearing a lot of phase weirdness?
Tim
Click to expand...
Don't know yet as I have just got an Mbox and some mics and am just starting down the home recording path. Can't do anything at the moment until my other PC gets fixed as the one I am on now does not have enough RAM :-(


Aaron
 
confusion over 3:1 rule...

First, i'm just curious as to why it actually makes it go out of phase if anyone knows. And second, I've gathered that it only really applies to mono recording from a sound source (like a guitar amp or speaker i'm assuming). About a year back I recorded an electric rhythem guitar part using two mics, one at the cone of the 12 inche speaker and one near the outside and adjusted each of the volumes and EQed a little till i got a nice thick sound. I didn't have any phase problems what so ever, so I must be missing something. I guess the bottom line really IS trust your ear.
 
You must log in or register to reply here.
Back
Top