Question On The 3:1 Theory

[metanoiastudios]

ashcat_lt mentioned to me that, along with the principle of the 3:1 (OR GREATER) rule, there is also a guideline of -9db or so. If the 3:1 theory is used to reduce phase issues in terms of time delay, how does volume come into place? perhaps this is related to the "comb filter" aspect of phasing?

[DJ_LBP]

i think it means that the volume difference between the two is so great, that the fluctuations due to cancellation are not audible. that's the way I'm reading it.

interesting stuff!

[Jon~T]

Rather than to start a new thread for the same topic, I'll resurrect this one.
Great posts btw, turned my concept of the 3:1 rule on it's head and now I don't know if I understand it better or worse.

Anyway, today I posted some pictures from a recent session and it's created a lot of controversy between me and the engineer.

The pictures can be seen here: http://www.audiogeekzine.com/?p=525
The final positions of the mics were more angled and about 1 foot back.

I suggested room mics next time, she said she prefers KISS and a 3:1 configuration worked with the mics used.
I say 3:1 rule doesn't apply to stereo miking.
The debate is whether this is a stereo miking situation (my opinion, as there are two mics panned left and right) or not because the mics aren't matched.
semantics ensue.
She refers me to http://www.recordingeq.com/articles/321eq.html
I ask where it says the word 'stereo' in the article (go ahead search!), and then it got worse from there.

Any thoughts on this?
3:1 apply in this situation?
stereo yay or nay?

[JohnDavisNYC]

that pin block sure must sound good!

[Jon~T]

helpful, thanks.

[farview]

The 3 to 1 rule has nothing to do with stereo mic techniques. It never did. Otherwise coincident pair and ortf wouldn't work.

The only reason the 3 to 1 rule works is because of the volume difference between the two mics.

[Jon~T]

The 3 to 1 rule has nothing to do with stereo mic techniques. It never did. Otherwise coincident pair and ortf wouldn't work.

The only reason the 3 to 1 rule works is because of the volume difference between the two mics.

That's what I've learned here in the past week, I'm looking for a text that specifically says 3:1 does not apply to stereo miking. It seems to be assumed almost everywhere that it does, and thats where this confusion comes from.

[Jon~T]

Then this goes and confuses everything again.
http://books.google.ca/books?id=Emke4iz ... t#PPA77,M1

[saint360]

The 3 to 1 rule has nothing to do with stereo mic techniques. It never did. Otherwise coincident pair and ortf wouldn't work.

The only reason the 3 to 1 rule works is because of the volume difference between the two mics.

Crown seems to agree with farview's way of looking at the 3:1 guideline:

http://www.crownaudio.com/mic_web/tips/mictip6.htm

[locosoundman]

Looks like the article SHE referred you to actually says it flat out:

The Three To One Rule works on the basis of using distance to reduce the pickup of one sound source in the microphone intended for another source.

Another note (though a bit off-topic in this case): your pic's show a C414 and a C3000 as a "stereo array" on the piano. Typically a 2-mic stereo array will consist of two of the same make and model of microphone.

[Jon~T]

miking the piano was a matter of 'look at this picture of how it was set up last time and do something similar. I would have loved to try out different positions, but it wasn't my session.

The way we miked it I would consider to be a stereo pair as it's one piano with two mics, on each side and panned away from each other.

[locosoundman]

Simply panning them hard left and hard right does not necessarily make them a "stereo array." This is where the ambiguity kicks in.

3:1 rule and stereo mic techniques are actually diametrically opposed to each other. In the case of 3:1, you are trying to minimise the interaction between two (or more) mics to get greater separation between microphones; with minimalist stereo techniques, you are trying to use the interaction between two (or more) mic's to create a cohesive whole.

It may be a matter of semantics, but with true stereophonic recording, you are trying to create a sonic "image": meaning that there will be localisation of sound sources between the speakers. This is achieved by a certain blend of similarity and difference between the signals being picked up/generated by each mic, which means that the one mic must pick up a certain amount of the same sound source that the other is picking up, else there will be no "image."

The placement and mic choices in the picture seem to indicate more of a "low string/high string" multi-mono approach to recording the piano. Due to the distance between the mic's and the fact that the frequency response of the microphones are not really the same, it probably would not generate a cohesive stereo image. In this case, if you are looking to de-correlate the low and high regions of the piano, the 3:1 rule could apply.

But, before you get out the protractors and tape measures: at the end of the day, if you and/or the musicians were happy with the result, this is all that really matters.

[firesine]

Then this goes and confuses everything again.
http://books.google.ca/books?id=Emke4iz ... t#PPA77,M1

Haha, that looks more like a 2:1 rule over the congas. If they want me to take their book seriously they should get better pictures and stop making up distances to support their conclusion.

Also, did it sound good?

If so, who cares?

I use two different mic's for stereo pickup all the time (especially MS) and I really don't think that matters. It's all about capturing the instrument in a stereo soundstage, not what kind of mics you use.

[locosoundman]

I use two different mic's for stereo pickup all the time (especially MS) and I really don't think that matters. It's all about capturing the instrument in a stereo soundstage, not what kind of mics you use.

This works for MS sometimes. I have had differing experiences - for instance once I was using KM140 for the Mid and C414 B-ULS for the side. The imaging was a bit weird - it would either be centered or stretch and/or collapse to one side or the other. When I replaced the 140 with another C414 B-ULS it worked much better. Using a KM120 with the 140 probably would have also worked well.

Any time you are mixing one of the mic's equally to both channels, it is easier to get away with using a different type of mic in the array. MS can work if the high-frequency response of the mic's is similar since the Mid mic gets mixed equally to both channels. Other situations where it could work are 3- or 4-mic techniques (Decca tree, M3 if the center mic is the different model or even M4 if you use two different pairs)

It depends on how anal you are about the imaging in the stereo sound stage. I am pretty anal about it (as if you couldn't tell ) since this type of minimalist recording is how I pay my rent.