if this is considered such a "no-no," why does it sound so good?

  • Thread starter Thread starter antispatula
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bubbagump said:
Explain then... I apparently don't know why the 3:1 rule exists then as I thought unless you were absolutely coincident (more or less) you would run into problems.
They are slightly offset in time which would have some effect on the top end (I don't know how high) but look at AB stereo and ORTF. There offset is intended to alow a little phase differences so it's not an either/or situation.
The main point though might be to know that 3:1 doesn't fix any phase frequiencies, it just attenuates cross bleed.
 
Hrm, then what the heck are they talking about here?

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

As I was always under the impression that comb filtering etc. creeped in. Or is this only in certain circumstances?

EDIT: This seems to explain it better.

http://www.prosoundweb.com/install/spotlight/bartlett/phase/phase.shtml

I get it now. Attenuation yes, but with the goal of minimizing phase issues in MONO.

What if two mics pick up the same instrument at different distances and they are NOT mixed to the same channel? You don't get phase cancellations. Instead, you get stereo imaging. The location of the instrument's image between your house speakers depends on the delay between mics, the levels at those mics, and where you panned them.
 
mixsit said:
They are slightly offset in time which would have some effect on the top end (I don't know how high) but look at AB stereo and ORTF. There offset is intended to alow a little phase differences so it's not an either/or situation.
The main point though might be to know that 3:1 doesn't fix any phase frequiencies, it just attenuates cross bleed.

With two mics an inch apart you may notice stuff starting around 5k.

As far as attenuating crossbleed- the magic level is around 9db. If you listen to two out-of-phase signals, once one of them is around 9db less in volume than the other, you won't hear audible cancellation, according to the propellerheads.

3:1 says if you put a second mic three times as far from the first as the first is to the source, the attenuation will be around 9db. So when you listen to both mics AT THEIR PROPER RELATIVE VOLUME you won't hear the comb filtering. It's still there, though.

3:1 is really about relative amplitude, not distance. 3:1 assumes the same mics set at the same gain and played back at their proper relative levels, ie the far mic is going to be down about 9db, just like you would hear it if you listened from one foot away and then backed off to four feet.

The classic misuse of this is a near/far mic on a guitar amp. You see it all the time.

"I put one mic a foot away from my amp and another three feet away, and I'm hearing comb filtering. Why? I followed 3:1"

No, you didn't. And you shouldn't have anyway.

First of all, the second mic is supposed to be at least three times farther from the first mic as the first mic is to the source, not three times the distance as the first mic is. So if your near mic is one foot away, your far mic needs to be at least four feet away.

Second, most people don't understand the amplitude thing. So they bring up their far mic track enough so it crosses that 9db threshold, and hear cancellation. And are confused.

Because thirdly, they thought there was a magic distance ratio that eliminates comb filtering. There isn't.

People who claim 3:1 spacing eliminates comb filtering when using a near/far mic placement have either 1) chosen a placement that puts the filtering either out of the audible range or in a range where isn't offensive or 2) unknowingly have the relative levels of their tracks set so the one is at least 9db quieter than the other.
 
The two mics in question are practically touching one another. I doubt there's going to be an issue.

.
 
This is all great info. I always thought the 3:1 deal was a wave length consideration (much like using 1/4 wave lengths in room treatment to knock things down), not attenuation. But it doesn't make sense the more I think about it as the 1 in 3:1 is not a constant thus wave length considerations will always differ. Reading the above and understanding the 9db difference translating to ~1db of comb filtering makes it clear.
 
How did you strum the guitar if you had 2 mics 4 inches from the soundhole?
Just curious.
 
bubbagump said:
.. the 1 in 3:1 is not a constant thus wave length considerations will always differ.
Ding! :D

mixsit said:
His (Anti's) 2nd is back a bit but not much. (='s some phase on the high end)..
And I should correct this. I initially thought the 2nd mic was 1" back from the first (as well as to the side). :rolleyes:

So let's make that '= distance =time =phase.'
Thank you. :)
 
tdukex said:
Sorry, the sound is not that good. It may not be boomy but it is bass heavey and compressed.

And ittam is correct, there is no stereo image.

You will almost surely be better off placing one mic at the 12th fret (or there abouts) and one at the bridge or bout.

Also, if the room isn't too crappy, back the mics off to about 12" and let the guitar breath just a little.

I actually like the sound I've produced, but to each his own.
I've tried the 12th fret practice, whith quite terrible results. I get a really ugly tone, and do not understand why. Perhaps I should expirement more, and either way appreciate the constructive critisism
 
antispatula said:
I actually like the sound I've produced, but to each his own.
I've tried the 12th fret practice, whith quite terrible results. I get a really ugly tone, and do not understand why. Perhaps I should expirement more, and either way appreciate the constructive critisism

So you have tried one mic 12" out from the 12th fret and another mic 12" out from the bridge and then panned them at 10 and 2 and got an ugly tone? Try the 14th fret and angle the mic slightly toward the sound hole.

If you are using a single mic I would point it at the neck joint, not the 12th fret.
 
antispatula said:
I actually like the sound I've produced, but to each his own.
I've tried the 12th fret practice, whith quite terrible results. I get a really ugly tone, and do not understand why. Perhaps I should expirement more, and either way appreciate the constructive critisism

which microphones have you tried? those small capsule measurement microphones sound pretty similar in various placements.
 
If it sounds good to you, it IS good.

All the general rules work most of the time in average situations on most equipment for most people.

Having said that:
I hate the sound of my own guitar if soundhole mic'ed. Too boomy, as one would expect.
I like omnis spaced about 10" apart at about 18" distance, centered between the 12th fret and soundhole. ...always in stereo, never mixed. That gives an "accurate" sound, but not necessarily an "enhanced" sound.
 
omnis are great for close up mic'ing, sdc or ldc also i pad down the ldc sometimes, and usually use hp filtr
 
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