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[timrob]

frank w.scott wrote on Sun, 06 November 2005 19:33

timrob wrote on Sun, 06 November 2005 23:03 The KM85 is known to have quite a bit more low end than KM84... While the highs are similar. The KM85 is the one with the built in bass rolloff.  It has a nice -12dB at 50 hz which starts the rolloff from around 200 hz. It was made for the spoken word.  It works quite well for any source with lots of bass and proximity effect.

Right. It needs the rolloff because the capsule has more bottom than a KM 84 capsule. At least that is my understanding. Even with a rolloff starting at 200 it won't be down that much between 150 and 200 which is where you generally will find boominess on Acoustic Gtr.

I've only used the 85 a couple of times. I tend to go for Shoeps with wide cardioid on Acoustic gtr. Much more natural highs to me.

[frank w.scott]

Eh... take a look at the freq curves for the KM85 and KM84.  I misquoted the rolloff start for the KM85.  It actually starts near 500 Hz.  At 200 hz it is -4Db, and -8Db at 100 HZ.  The KM84 is level down to around 200 hz where it then begins a slight rolloff to -3 Db at 50 HZ.

The KM85 was specifically designed to be used when proximity effect was NOT a desired effect, such as close speech.

The KM84 is vastly more "boomy" than the KM85.  I own and use both.

[timrob]

frank w.scott wrote on Sun, 06 November 2005 21:08

Eh... take a look at the freq curves for the KM85 and KM84.  I misquoted the rolloff start for the KM85.  It actually starts near 500 Hz.  At 200 hz it is -4Db, and -8Db at 100 HZ.  The KM84 is level down to around 200 hz where it then begins a slight rolloff to -3 Db at 50 HZ. The KM85 was specifically designed to be used when proximity effect was NOT a desired effect, such as close speech. The KM84 is vastly more "boomy" than the KM85.  I own and use both.

Ok, You got me. Still with that much rolloff, why should you even need to consider flipping phase/polarity on a channel to control low end.?

[Barry Hufker]

Getting back to polarity, A/B stereo can never be (or at least shouldn't be) totally in phase.  That's because it relies on time of arrival (phase) and amplitude to achieve stereo.  The only time both mics might be exactly in phase is if they are mounted one above the other.

And in using the 3 to 1 rule, you are (according to the rule) trying to keep one source from leaking into a nearby mic.  So, I don't get why you'd want the 3 to 1 rule, then potentially you don't have a center in your stereo image.  The way it's mic'd at the moment it should almost be as tho' you have no common signal and therefore no in-phase signal between the two channels.

Barry

[frank w.scott]

Depending upon the type of instrument, and it's own tonal attributes will dictate what setup I use.  There are times when I want the raw tone of an instrument to come through, in this case an acoustic guitar.  This requires relative close miking to pinpoint areas of the guitar that will reproduce the raw tone.  Other times I may not want the raw tone, such as violin, however I won't be using a stereo setup on the violin.

If you look at my previous post on page 1, I can manipulate the amount of phase from completely -1 to solid +1 by how much each mic is panned into the other.  So it all really depends upon what sound or tone I'm looking for.

I've found this phase thing to really be interesting.  I think what is occurring is that only the low frequencies are being phased out up to a _certain degree_ and that can be adjusted by how much I pan each track into or away from each other.

Even using mics like the KM85, proximity affect on the acoustic guitar is a reality when doing close miking (8-12 inches), but I cannot and have never figured out another way to achieve raw tone without dealing with this proximity affect.  At least until now.

I'll perhaps post an mp3 of my results sometime.

[timrob]

Barry Hufker wrote on Sun, 06 November 2005 23:51

Getting back to polarity, A/B stereo can never be (or at least shouldn't be) totally in phase.  That's because it relies on time of arrival (phase) and amplitude to achieve stereo.  The only time both mics might be exactly in phase is if they are mounted one above the other. And in using the 3 to 1 rule, you are (according to the rule) trying to keep one source from leaking into a nearby mic.  So, I don't get why you'd want the 3 to 1 rule, then potentially you don't have a center in your stereo image.  The way it's mic'd at the moment it should almost be as tho' you have no common signal and therefore no in-phase signal between the two channels. Barry

Well, I guess stereo miking is the one area you get to disobey the 3 to 1 rule for effect.

With any non conincident pair you'll have acoustic phase differences dpending on the spread. But you'll never have a signal 180 degrees out of phase unless a mic's polarity is electrically inverted.

We use the terms phase and polarity interchangably sometimes(as I'm certain you understand), but one has to be careful because they are actually two different though related things.

As I understand it, phase has a time component where polarity does not.

What Frank is talking about here has little to do with stereo. I think he agrees that a wide spread sounds strange with polarity reversed. So with that technique you are limited to pretty much a mono or near mono representation. Of course, you still have the option of flipping polarity back to normal after the fact. So you still really have all options available.

Years ago, I experimented a lot with micing Guitar Amplifiers using 2 microphes. One close and one far, inverting the phase of the latter and playing with the distance. It gave some interesting results. In the end it was more of a "hey, look what happens when I do this" kind of thing. After a while, I lost interest, because it wasn't a 100 percent reliable tactic. I didn't always have time to dink around with a mic that really wasn't contributing that much to the overall picture.

Frank, I'm glad you found a technic that works for you. It is not for me and I can't help thinking you might get better results by varying distance and angle of the microphones to get the sound you're after.

Peace,

[frank w.scott]

Quote:

What Frank is talking about here has little to do with stereo. I think he agrees that a wide spread sounds strange with polarity reversed. So with that technique you are limited to pretty much a mono or near mono representation.

I agree, I'm not trying to get stereo, I can get that easily, nor is my issue with the phase, I can handle phase and can have two mics perfectly in phase if I wanted to.
My only issue here is the _proximity affect_ with close miking of certain instrumetns most notably the acoustic guitar, but not just your typical chunky bright guitar we have all come to know and hear in most pop music.  The acoustic guitars I am referencing are along the lines of Martin, Santa Cruz, Gallagher, etc... These dreadnought guitars have a tremendous amount of low-end boost when close miking.  

But I disagree on the amount of stereo I can get when phasing out the low end.  The mid-low to high remains at least in this scenario, and it may change with a different set of mics, albeit I'll have to reconsider.

Quote:

Frank, I'm glad you found a technic that works for you. It is not for me and I can't help thinking you might get better results by varying distance and angle of the microphones to get the sound you're after. Peace,

I know of a technique used by a couple of engineer's of whom I respect deeply where they induce phasing by varying the distance of one mic to the other.  They will position one mic farther away from the source than the other mic until they hear the target frequency they want to cut begin to fade out.  Usually this is going to be the low end.

It is shaping response by phasing.  I would love to learn how to do this but I do not have the experience or the patience.

[timrob]

FWIW, I work with Folk and Bluegrass artists and record these types of instruments all the time. Martin, Collings, Santa Cruz, Taylor, Gallagher, NGC...etc.

[frank w.scott]

Then I suppose you are pretty familiar with Billy Wolf's methods of recording acoustic music.  Someday I'd like to be that good.  Proabably not in my lifetime.  Funny thing is tho, some folks don't like the tone he gets, I grew up on it.

[timrob]

Well, I'm not particularly familiar with exactly what methods he uses. I like a lot of the records he's done.
I can imagine he uses microphones, preamps, eqs, and compressors though.

[frank w.scott]

I would if I was recording a band, but my main stuff is usually one instrument or two at the most.  I'd like to be able to record a whole bluegrass band or soemthing of that nature but alas my talent is within the confines of single instruments.

Cheers, I think this thread is exhausted.

[crm0922]

frank w.scott wrote on Sun, 06 November 2005 16:31

- Full pan left and right: Completely out of phase, jumps between -1 and 0.  Extreme wide stereo (false sounding). - Pan left 50%, right 50% Jumps between 0 and +1, in phase although not completely. - Pan left 50%, right 0% Completely in phase, stays solidly at +1 - Pan left 20%, right 20% Completely in phase, stays solidly at +1 So, anyway it seems I can have my cake and eat it too.

No one else seems to have pointed out the fallacy in this experiment.  You seem to be missing the fundamental science behind what is going on here.

In your first "completely out of phase" test with the hard panning, you are seeing the actual signals' phase relationship.  Almost completely out of phase.  This is generally not a good thing unless a phasey special-effect is desired.

As you are panning them closer towards the center you are NOT removing signal from left and right, you are simply adding more of the left signal to the right and vice-versa.

Big surprise, the signal becomes more and more in-phase as left and right become more and more the same.  If you used two fully out-of-phase sine waves you would achieve the same result.  Complete nulling of the signal, but no out-of-phase content at all when both are panned center.  Maybe a better test is 1k on each side and 2k on one side only.  As you pan inwards, you'll be left with only 2k signal if the 1k components were at an equal level.  Now imagine that at integral-multiple relatitionships to the mic distances up and down the frequency spectrum...

The fact is, there is massive comb-filtering happening if the mics are in front of the same instrument and one mic is polarity flipped.  The fact that this sounds ok to you notwithstanding, the conclusion that the phase error doesn't happen as you pan inwards is incorrect.

The 20% pans and 0%/20% are only revealing the limited resolution of the phase analysis.

If you want a more natural sound, this would be the dead last thing you should do.  The sound will change based on panning, but also based on speaker distances, listener's rooms, your head position, etc. after the recording is a done deal.  This is why keeping a modestly accurate phase relationship using multiple mics is a goal for better sound.

If the proximity effect is bothering you, perhaps try omni mics?  Intentionally comb-filtering with left and right pairs sounds dangerous to me as well.

Chris

[frank w.scott]

"Intentionally comb-filtering with left and right pairs sounds dangerous to me as well"

I'm not understanding this.  Dangerous in an electrical kind of way as in dangerous to the mics' circuits or just dangerous ina  final sound/listener kind of way?

I agree with everything else you said.  Mono sounds excellent, and I'm able to shape the sound to my taste.  I'm varying the left and right signals between 10%-40% pan depending upon the sound I want.  And with it being in phase as the unwanted signals are cancelled out, it's sounding good on various speakers and distances.

Another neat thing that can be done is to raise or lower the volume of one channel to further change the sound in case I want more of one mic than the other.    

[CHANCE]

An audible example of using phase cancellation, is in TV news helicoptors. There are 2 mics in the chopper, one for vox, and one for ambiance. The vox mic cancells out the ambient noise of the helicopter. On one occasion I heard a very unusally noisey chopper sound. I called my local TV news, and when they showed the next traffic break, they even announced that they had to change a mic cable. (it was out of phase) I used to have this problem with some old Euro cables. I believe the Brits used to use pin #1 (vs pin #2) hot in their XLR connections

[wavdoctor]

My first thought was a bad (or miswired) cable, But the results would have been opposite of his findings..? no?

HB