Question On The 3:1 Theory

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Question On The 3:1 Theory

Post by akg414 » Wed Jun 04, 2008 8:16 am

The theory of 3:1 states that for every unit of measure the mics are awayf from the source, they should be 3 units of measure away from each other.

For overheads, where does the source get measured FROM? The toms are lower that the cymbals, and the snare lower that the toms.

Is it simply a case of using a happy-medium? For example, using the toms as the point of source (since the snare is lower and cymbals are higher)...

What does everyone do in this situation?
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Post by locosoundman » Wed Jun 04, 2008 9:01 am

The three to one rule applies to spot mic'ing - e.g. if you have a trumpet player and a saxophone player in the same room, and you put a microphone on each instrument, the saxophone player should be much closer to his mic than he is to the trumpet mic and vice versa. When mic'ing up a drum kit, this would apply to the individual drum mic's - the diaphragm of the snare mic should be at least 3x closer to the snare than it is to the high hat.

With overheads, you are dealing with a different scenario. Rather than trying to pick up a single instrument with a single mic, you are generally trying to pick up multiple instruments with (usually) a pair of mic's. The two mic's are acting more like your ears - they are working together as an array to reproduce the sound of the drum kit. 3:1 does not apply here. In this case, you are placing the mic's in such a way that you will pick up a blend of the overall kit. Rather than thinking of each drum individually, you are mic'ing the entire drum kit as a single instrument (sort of).
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Re: Question On The 3:1 Theory

Post by chris harris » Wed Jun 04, 2008 9:19 am

bradjacob wrote:What does everyone do in this situation?
leave the tape measure in the toolbox and put the mics where they sound good.

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Post by the finger genius » Wed Jun 04, 2008 9:33 am

locosoundman wrote:The three to one rule applies to spot mic'ing
I don't think this is entirely accurate. First of all, it's more of a guideline than a rule, but I do think the three to one rule can be very helpful in getting a good stereo image of a single source when using a spaced pair. Of course, a drumset is not really a single source, which is the issue. If you've ever tried recording a drumset with the mics right next to each other, you'll notice no stereo image, if they're 9 feet apart and a foot and a half off of the center source, you may notice that there is no "center" in your recodring.

Many times drum mic placement / distance is determined from the snare drum, where the snare is considered to be the kit's center (such as in the Glyn Johns technique.) Usually, this is the case when two mics are essentially being used to capture the entire kit.

In this case, I think you'll need to make a decision about what you want your overhead mics to do; in other words, should they be mainly picking up cymbals, with toms kick and snare supplemented by mics with their own sound, or do you want your overheads to capture the sound of the entire kit?

This can depend greatly on the drummer, and the set your recording. In general, I like to capture an overall kit sound with my overheads, and will choose a spot somewhere in between snare and cymbals somewhere near the drummer's chest (unfortunately, it's not an exact science, or at least if it is, I haven't mastered it yet.)
Last edited by the finger genius on Wed Jun 04, 2008 9:34 am, edited 1 time in total.
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Post by farview » Wed Jun 04, 2008 9:34 am

The 3 to 1 rule does not apply to stereo micing techniques.

The 3 to 1 rule is about isolation. The most common use for it is when there are multiple instruments playing in the same room, each with their own mic. Like the trumpet player and the sax player in the last post, the sax player needs to be three times farther away from the trumpet mic than the trumpet player is, otherwise you will end up with phase cancelation due to bleed.

Which brings us to another source of confusion about the 3 to 1 rule: Phase. The 3 to 1 rule can make it easier to avoid phase problems, but only because it isolates one mic from the other. It's the isolation (the lack of bleed) that keeps the phase problems in check, not because it's some magic point in space where all the frequencies become time-aligned. (that can't happen)

As long as the two mics are at equal gain (not equal volume) the signal coming out of the distant mic will be 9db lower than the close mic. That difference in volume makes the phase cancellation (which is still there, by the way) so quiet that it isn't a problem.

However, if you match the volume of the close and distant mics, you will have all the phase problems you would expect.

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Post by locosoundman » Wed Jun 04, 2008 2:12 pm

To be even more precise, the 3:1 rule (guideline, theory, whatever) applies to multiple sound sources with the same intensity level (more or less). It wouldn't help you much if you were trying to record an mbira in the same room as a Marshall stack.
If you've ever tried recording a drumset with the mics right next to each other, you'll notice no stereo image, if they're 9 feet apart and a foot and a half off of the center source, you may notice that there is no "center" in your recording.
This could open a whole other can of worms. but you are correct in that there is a correlation between the distance between mic's and the distance to the sound source in a spaced-mic stereo array. Generally speaking (not taking into account any directional characteristic), the closer the array gets to the sound source, the closer the mic's must be to each other to maintain a coherent image. Of course, there comes a point at either extreme where the mic's are too close or too far apart to maintain the image - either there is too much correlation (mono) or too little (hole-in-the-middle) - but all that is off topic I think.
leave the tape measure in the toolbox and put the mics where they sound good.
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Post by rhythm ranch » Wed Jun 04, 2008 5:01 pm

farview wrote:The 3 to 1 rule is about isolation... The 3 to 1 rule can make it easier to avoid phase problems, but only because it isolates one mic from the other. It's the isolation (the lack of bleed) that keeps the phase problems in check, not because it's some magic point in space where all the frequencies become time-aligned. (that can't happen)
To follow up on farview's post - The "3" is also non-magic because it's a minimum, which is why it's at least 3:1.

Because the "rule" depends on isolation, the farther, the better.

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Post by Professor » Wed Jun 04, 2008 6:22 pm

Well said by everyone.

I like to teach it as the "Greater than 3 to 1 recommendation" because of all the confusion that seems to surround how it is usually taught.


I'll also toss in the notion that as a ratio it is reversible, meaning that the distance between two mics can be the "1" and the distance from the mics to the source can be the "3". That helps make sense of something like an ORTF pair over a drumset.


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Post by rhythm ranch » Wed Jun 04, 2008 7:49 pm

Excellent point (as usual) Jeremy.

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Post by rwc » Wed Jun 04, 2008 10:05 pm

what makes more snese to me is having the mics not pick up the same thing. the 3 to 1 rule is one way of not having mics pick up the same thing, but it confuses people who ask "then how does ortf/XY work?", Unless you want to use phase fuckups to your advantage, which is something I wouldn't recommend to anyone who hasn't already made great, phase coherent, interesting recordings, I say fuck this rule, and go for what sounds good, and try to keep a stereo pair from picking up the same thing. get to know your mic's pickup pattern, and how it hears things. Get to know how it hears things in conjunction with the other mic you are using for a stereo pair, whether it is matched or not. instead of aiming to obey the 3 to 1 rule, aim to do what the 3 to 1 rule is trying to get you to do in the first place.. keep you from pointing two mics at the same shit from different places.

the 3 to 1 rule exists to keep you from having mics pick up the same shit and cancel out, like a spaced pair 20 feet over a piano that are pointing down, parallel, that are 3 feet apart. but you can do this with mics right next to each other far from a source.. like blumlein, or xy, or ortf.. so fuck this rule!

like when newscasters get close together and you can't hear them as well.

there's also a sick world of sonic creativity between phase coherency and total mess that creates larger than life sounds and stereo fields you'll never get from adding reverb, panning, or standing in the room.

but, you can also dig a miserable hole for yourself when stuff sounds like cock and balls. this is why listening to what you are doing is important when you are doing some retarded bullshit to get a sound you want. do not satisfy yourself with being impressed by the fact that shit works and you hear something faintly resembling a drumset, or a choir, or a piano while recording. Do not satisfy yourself with the fact that musicians aren't walking out on you because of your perceived incompetence. Do not fear that musicians will get pissed off at you taking time to dial in a sound, because it's them who will ream your ass for the rest of your life to everyone they meet when their record sounds like unrefined crap!

do not stop moving shit, swapping shit, hacking away in the daw/console until you have something that sounds like what you have in your head. and if you have nothing in your head, get something in your head that sounds like a finished record by listening to everything you can, from every genre, on as many stereos as you can, for the rest of your life.

it's your trip.. have fun. :)

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Post by mwingerski » Wed Jun 04, 2008 11:19 pm

????? wrote:

do not stop moving shit, swapping shit, hacking away in the daw/console until you have something that sounds like what you have in your head.
.
At what point do you have to quit worrying about whether or not you've got the perfect stereo sound and start to worry about whether or not you're going to get a decent performance out of a bunch of worn out musicians who are wondering why the hell you're tweaking around with 30 different mic positions.

At some point, it moves out of theory and into reality. 3:1 is often useful. But listening is the important part.

Keeping a session moving is more important than anything else.

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Post by rwc » Thu Jun 05, 2008 4:20 am

mwingerski wrote:Keeping a session moving is more important than anything else.
Keeping a session sounding good is more important than anything else!

Especially if your material is going to be mixed by someone else. If you have to mix your own crap, you can badmouth yourself to yourself. If someone else gets junk, they'll badmouth you to everyone. Having other people mix your work is like having your mom and dad visit come parent-teacher conferences.

There's a balance between keeping a session moving, and taking that little extra time while the musicians are talking to each other, tuning their instruments, rehearsing, and getting their shit together to get 500% better sounds to disk/tape. The people who understand how to work that balance without stopping the flow of a session make the difference between "legitimate engineer" and "POHDUZAH!", IMO.
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Post by MoreSpaceEcho » Thu Jun 05, 2008 5:44 am

????? wrote:Keeping a session sounding good is more important than anything else!
+1 million.

of course you always try to work as fast and as unobtrusively as possible, but if shit isn`t working that great, then definitely take the time to fix it or you`re gonna be paying for it later.

in my experience, musicians have NEVER minded me taking a minute to tune or swap out a snare, fuck with mic placements or whatever. they understand that i`m doing it to make their record sound better and generally, people like that.

if i can be patient with them figuring out their parts in front of the mic for an hour, they can be patient with me moving said mic for 2 minutes.

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Post by roscoenyc » Thu Jun 05, 2008 6:55 am

like the Proff said 3:1 is a suggestion.

main places I use it...


1. If I've got a band playing open (w acoustic and or amps) together in the room I'll measure the OH to Snare and set up the band that distance X 3 around the drums probably with some go-bo's too. This same thing works well for a live vocal in the room (especially with a mic like the M-500 positioned null towards the drums)
Also good distance for room mic.

2. multiple mics on a guitar cabinet

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Post by farview » Thu Jun 05, 2008 9:04 am

????? wrote:what makes more snese to me is having the mics not pick up the same thing. the 3 to 1 rule is one way of not having mics pick up the same thing, but it confuses people who ask "then how does ortf/XY work?", Unless you want to use phase fuckups to your advantage, which is something I wouldn't recommend to anyone who hasn't already made great, phase coherent, interesting recordings, I say fuck this rule,
The 3 to 1 rule does not apply to any stereo micing techniques. XY doesn't have any real phase problems because the mics are so close to each other that the sound hit both at about the same time.

Phase is a time shift. Any time you have two mics at different distances from a source, you will have phase discrepancies. They could sound good, they could sound bad, but they are always there. Those timing differences are one of the things that give our brains the spacial cues that allow us to know the direction of a sound.

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