Question On The 3:1 Theory

[locosoundman]

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

YES! YES!

PLEASE do not associate 3:1 with anything related to stereo mic techniques.

Jeremy - I love you man, but PLEASE don't mention 3:1 (or 1:3) in the context of ORTF or AB mic spacing. For stereophonic techniques it is the source angle/width with regard to the mic array that determines the spacing/angling of the mic's and the distance to the ensemble. For example: the ORTF array (110-degrees/ 17cm) is optimised for a 90-degree source angle. Also, the proper amount of interchannel correlation of amplitude and phase must be taken into account.

Please reference Farview's first post - which covers the whole 3:1 thing with absolute clarity. 3:1 has NOTHING to do with phase coherence, it simply is a guideline to minimize phase cancellation between adjacent spot mic's under the right set of circumstances.

It will also help ensure that you get the sax in the sax mic and the trumpet in the trumpet mic and that you can adjust their relative balances (within reason) without coloring the other open spot mic's.

[akg414]

So this would be good for two mics used to record an acoustic guitar - 3:1 away from the guitar...?

Does this work for two mics on a guitar cabinet (with on speaker) as well?

[farview]

So this would be good for two mics used to record an acoustic guitar - 3:1 away from the guitar...?

If you want a close mic and a far mic on the guitar, sure. If you are trying to mic it in stereo, no.

Does this work for two mics on a guitar cabinet (with on speaker) as well?

Only with a close mic and a distant mic as long as you leave the distant mic quieter than the close mic.

The 3 to 1 rule really didn't have much to do with using two mics on one source. It's about isolation. You can get the same effect by putting two mics anywhere you want and just make sure to turn one of them down so it is at least 9db quieter than the first one.

[akg414]

So this would be good for two mics used to record an acoustic guitar - 3:1 away from the guitar...?

If you want a close mic and a far mic on the guitar, sure. If you are trying to mic it in stereo, no.

Does this work for two mics on a guitar cabinet (with on speaker) as well?

Only with a close mic and a distant mic as long as you leave the distant mic quieter than the close mic.

The 3 to 1 rule really didn't have much to do with using two mics on one source. It's about isolation. You can get the same effect by putting two mics anywhere you want and just make sure to turn one of them down so it is at least 9db quieter than the first one.

Ok, (forgive me), but I'm a bit confused, and a bit getting it.

Can you give me a real world example of where/when to use a 3:1 ??

[chris harris]

Ok, (forgive me), but I'm a bit confused, and a bit getting it.

Can you give me a real world example of where/when to use a 3:1 ??

If you're recording two people in the same room. Say you've got a guy playing banjo and a guy playing fiddle. you want the fiddle player at least 3 times further away from the banjo player's mic than the banjo player is.

[akg414]

Ok, (forgive me), but I'm a bit confused, and a bit getting it.

Can you give me a real world example of where/when to use a 3:1 ??

If you're recording two people in the same room. Say you've got a guy playing banjo and a guy playing fiddle. you want the fiddle player at least 3 times further away from the banjo player's mic than the banjo player is.

Got it. Much clearer now.

The thing that got me confused is in Bobby Owsinski's book (Engineer's Handbook), he shows two conga drums - with two (AKG 451) over head - and it has arrows showing 1 foot up, and 3 feet apart. Misleading because it looks as if they're miked for stereo.

[ashcat_lt]

Also, as mentioned before, in close micing a drum kit. You want the hi-hat mic 3 x as far from the snare as the snare mic (and vice versa). Also (this is a bit different) can help when choosing placement for monitors on stage in a live setting.

Can anybody offer a more in depth explanation of why 1:3 works? I can dig that in XY the mics are close enough that the comb filter happens in the ultrasonic frequency range, but I'm not quite getting it otherwise.

[farview]

Can anybody offer a more in depth explanation of why 1:3 works? I can dig that in XY the mics are close enough that the comb filter happens in the ultrasonic frequency range, but I'm not quite getting it otherwise.

3 to 1 has nothing to do with stereo mic techniques, it never did.


The only reason the 3 to 1 rule gets rid of phase problems is because the far mic is much quieter than the close mic. That's it. There is no magical explanation beyond that.

[farview]

The thing that got me confused is in Bobby Owsinski's book (Engineer's Handbook), he shows two conga drums - with two (AKG 451) over head - and it has arrows showing 1 foot up, and 3 feet apart. Misleading because it looks as if they're miked for stereo.

Were they actually talking about the 3 to 1 rule? Or did you just assume because of the dimensions?

[akg414]

The thing that got me confused is in Bobby Owsinski's book (Engineer's Handbook), he shows two conga drums - with two (AKG 451) over head - and it has arrows showing 1 foot up, and 3 feet apart. Misleading because it looks as if they're miked for stereo.

Were they actually talking about the 3 to 1 rule? Or did you just assume because of the dimensions?

Yeah it was the whole 3:1 rule. I wish I had a scanner, I'd post the picture. He's talking about phase problems, and then show these two congas with the two mics directly over each drum. With a super-imposed arrow from the skin to the mic (1 foot), and from mic to mic (3 feet). It easily makes you believe it's for miking one source with two mics.

Anyone else have this book and can relate?

[Professor]

Jeremy - I love you man, but PLEASE don't mention 3:1 (or 1:3) in the context of ORTF or AB mic spacing.... etc.

Maybe you misunderstood what I meant there - serves me right for not writing one of my usual long posts.
What I have observed among young-uns, newbies, and the mis-informed, is a lot of confusion about what the 3:1 rule means. I've heard lots of guys ask, 'why would an XY pair work for an orchestra when the mics are 20-feet from the source, and the 3:1 rule says the mics should be 60-feet apart'. (That was actually asked at an AES Convention workshop, and the presenter responded, "those would be panned in stereo so it doesn't matter".)
What I try to explain is that the concept is used when one source is likely to be picked up in two mics, or when two sources playing similar or identical material will be picked up in one mic. (Although we usually illustrate something like two trumpets with a mic each, and mean for the 3:1 concept to apply to Trpt-A & Trpt-B both arriving in mic-A, and separately Trpt-A & Trpt-B reaching mic-B, that is really two instances where the concept applies.)
In general, when we think of a stereo configuration like an XY or ORTF or similar setup, we can think of it as two mics capturing one source - even if that one source is a whole drumset or a whole orchestra. If there are two trumpets playing in unison within an orchestra, we're going to get phasing of the sounds in the natural acoustic, and no amount of adjust ment of the mics will stop that, it's the fault of the composer for writing only 2 players on the unison instead of 3, and the fault of the conductor for not adding another player anyway.


But either way, it's often explained in very unclear, misleading, or just plain wrong ways. And it's also often taught along with a few laws of physics (like delay from the speed of sound, or proximity effect) and maybe with a psychoacoustic phenomenon (like the precedence effect). When it's placed in among a few "real laws" it comes off sounding like a hard and fast law in itself... not a recommendation, and not a flexible concept. I have no doubt there are guys out there with measuring tapes, moving their mics closer together to make sure they are exactly 3:1 off the sources.

-Jeremy

[roscoenyc]

Can you give me a real world example of where/when to use a 3:1 ??

these are the 2 main ways I use 3:1 (from the page before)

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

[JGriffin]

The thing that got me confused is in Bobby Owsinski's book (Engineer's Handbook), he shows two conga drums - with two (AKG 451) over head - and it has arrows showing 1 foot up, and 3 feet apart. Misleading because it looks as if they're miked for stereo.

Were they actually talking about the 3 to 1 rule? Or did you just assume because of the dimensions?

Yeah it was the whole 3:1 rule. I wish I had a scanner, I'd post the picture. He's talking about phase problems, and then show these two congas with the two mics directly over each drum. With a super-imposed arrow from the skin to the mic (1 foot), and from mic to mic (3 feet). It easily makes you believe it's for miking one source with two mics.

Anyone else have this book and can relate?

It's two congas though; it isn't one sound source, it's two.

[farview]

It's two congas though; it isn't one sound source, it's two.

But the congas are much closer to each other than they are to the mics. Both mics would really 'see' both congas equally. The 3 to 1 rule would apply if they were close micing each drum.

[Professor]

It's two congas though; it isn't one sound source, it's two.

But the congas are much closer to each other than they are to the mics. Both mics would really 'see' both congas equally. The 3 to 1 rule would apply if they were close micing each drum.

That's exactly why people get confused by those explanations.
Because there are two microphones, there is a possibility of having a phase problem between the two for each of the two drums. That is, strike the low drum and its sound will arrive at both microphones, then strike the high drum and its sound will arrive at both microphones. Two drums plus two mics just means two different ways to have a phase problem.
And of course, if they explain that the solution is to spread the microphones further apart so they are 3x or more the distance from the drum to the mic. Let's say they are 12" above the drums, so the engineer spreads them 36" apart. OK, but if the distance from the drum to each mic isn't equal or different by a factor of 3 or more, then he hasn't really done it right.
Very rarely does anyone explain that you can still observe the recommendation by "shrinking the 1" rather than "multiplying by 3". In the conga example, it the engineer drops the mics down closer to the drums, then distance from source-to-mic is shrinking, and 3x that distance is easier to achieve.



I do have a few real world examples where this effects what I do.
A couple of times each semester we bring the school big band into the studio, and the ensemble director likes to record the entire band live. I have to place 14 horn players in the same room. That's 4 trombones, 5 saxes and 5 trumpets. We have also found that it works better for the recordings to have an individual microphone on every one of those horns. That means 5 trumpets lined up almost shoulder-to-shoulder with a mic in front of each one, and then 5 saxes sitting next to one another, etc.
Do I sit there and frantically measure out the distances?
Nope. I walk around the room, have the players put up their horns to where they are comfortable playing and reading their music, and I place the mic in front of them, and fairly close to their instrument. I tell them that is where I want them to aim, and that is the distance I want them to maintain.
Does it work?
Yeah, for the most part.
The distance helps. The fact that they are mostly cardioid mics helps (because off-axis sounds are already down a few decibels). The fact that the mics are all dynamics helps a bit too.
Altogether, the recording method is the generally the least of our problems. And after cutting all the tracks in PT when the players aren't playing (what I call 'manual gating'), panning, a little light compression, some reverb, and a good once over for level balance, we get some good mixes. (PM me if you want a link to hear some.)


-Jeremy