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  #16  
Old 11-05-2011, 08:10 PM
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Originally Posted by Ty Ford View Post
FSC,

Yes I am. I have recorded with matching pairs. That's nice, but the more mics the better your space has to sound.


For solo guitar, one schoeps works nicely for me because I fill the sound space with two stereo reverbs during the mix.

Regards,

Ty Ford
I have to agree with Ty here, On two points 1. I really like one Schoeps CMC64. As far as two mics or one both techniques are viable. I think this has been discussed on a thread a while back

There are different opinions on recording an acoustic with one mic or two. And no real right or wrong, just preferences.

Many perhaps even most, prefer 2 mics feeling that it gives a nice stereo width to the sound.
However there is the fact that two or more mics does introduce phase into the equation, always.... Now how much phase and what that phase may sound like i.e. pleasing or not, depends on a multitude of factors. Mic placement being a primary factor along with room nodes freq. response etc. etc. plus if the phase gets to be too much, most DAWs have a means of flipping the phase on one mic or or one track, either during tracking or mixing.

Like Ty if I want a stereo sound there is alway reverbs, delays, stereo imagers.
or what I often do is simply dup the one track and slip (in time) the dup a few milli seconds. Then pan to taste. Of course verbs, delays, imagers and duping/slipping, also introduces phase, again its a matter of how much and how pleasing or not. Perhaps the only practical difference being, in the mono case, the phase is introduced at the mixing stage and is removable or changeable, instead of actually being recorded into the track. But in the end a matter of taste.
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  #17  
Old 11-06-2011, 06:05 AM
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Thanks Kev,

Phase cancellation due to multiple mics can also make a stereo mix sound really weird when it's played back in mono. You might think, "Mono!? Who would ever use mono!?"

Truth is, FM radios, when they can't get a strong enough signal to make stereo happen, fold the audio to mono automatically. Your clock radio is probably mono. Live PA systems are, more often than not, mono. Overhead systems in restaurants and stores are usually mono. Elevators? Mono.

The classic spread sound of a Yamaha DX7 keyboard infatuated many folks until it was time to fold it down to mono and then it pretty much disappeared due to phase cancellation! That's why I really line the Digi 003 and Mackie Big Knob. They have a front panel mono button that lets you quickly hear what your mix sounds like in mono.

The whole idea behind using matched mics as a stereo pair is to reduce phase cancellation and maintain a solid sound. There are many positions for stereo mics; XY, AB, ORTF to name a few. Each have strengths and weaknesses. I like coincident XY because the capsules are as close to being in the same space as possible, which greatly reduces phase cancellation.

For acoustic guitar, you can even try setting a stereo pair up on the vertical axis (bass/treble strings) rather than the horizontal axis (neck/body). That's more interesting to me for acoustic guitar because it's not really a stereo instrument. Yes, you listen to it with two ears in a space, but people have been trying to recreate the binaural effect of human hearing for years. They've gotten something different, but it rarely sounds exactly like what you hear sitting in front of the guitar because the pinnae, ear canals and brain are such a mighty processor.

Mic patterns can make an unexpected difference. Omnis are seldom omni directional at all frequencies, especially high frequencies. So you can get a really interesting stereo image using omni mics as well. And it will be mono compatible. Try two vertically coincident omnis. One on top one on the bottom facing the source and twisted slightly left and right to get a stereo spread on just the high frequencies.

Regards,

Ty Ford
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  #18  
Old 11-06-2011, 07:43 AM
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One mike on an acoustic guitar has always sounded phasey to me either in my recordings or recordings by anyone else. I think this is due at least in part to the rather broad area the guitar's sound comes from. It is not like a narrower sound source like say the voice or a flute. With more than one mike your brain interprets some of the phase issues as spacial information and the sound is more solid, though perhaps less focused in location. MS recording would be something to consider as a middle ground although I have settled on the spaced pair setup.

Oh, by the way if you use delay, reverb, etc to expand the sound stage of a mono recording you will have issues if that is then played back in mono just like a stereo recording has problems when played back in mono.
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  #19  
Old 11-06-2011, 08:35 AM
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A single mic on an acoustic guitar that sounds phasey is due more to the environment or to the poor off-axis response of the mic itself. All mics are NOT the same. That's why I keep mentioning the Schoeps cmc641. Somehow they have managed to make its off-axis response sound very coherent (less phasey).

It has been long held that SD mics are superior to LD mics for acoustic guitars because of off-axis problem on the wider diaphragms LD mics. Once more transparent headgrilles were used, e.g. Neumann TLM 103 and TLM 149, it became apparent that the headgrille itself was part of the problem. Sound passing through the headgrille would bounce around inside the capsule before and after it hit the diaphragm because the headgrille was stopping it from exiting. Reflected sound intermingling with the direct sound results in phase cancellation.

The TLM 103 and TLM 149 mic grilles are visually and, as it turns out, acoustically more transparent. While grille transparency itself is not the only factor, having a transparent headgrille makes a big difference.

Some mics are more "beamy." In that case, the diaphragm and capsule are creating frequency response anomalies where a frequency or frequencies are more (or less) linear depending on the specific angle that the sound strikes the mic and diaphragm. These are sometimes, but not always, more apparent around the edge of the pattern of a directional mic. It's weird, but I have heard them.

I learned about this by the generosity of mic design engineers at Neumann, Gefell and Schoeps whom I met while reviewing mics for trade magazines.

Regards,

Ty Ford
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  #20  
Old 11-06-2011, 08:50 AM
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I have the TLM 103 and it has the same issues with a single mike on an acoustic guitar. Ultimately it is what you are listening for and what you want to hear that makes your recording choices (that and your budget).
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  #21  
Old 11-06-2011, 09:20 AM
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No question that one mic on an acoustic gtr will sound different than two mics,
and of course which one is preferable is a subjective preference.

Also the problem with any discussion on Phase or more specifically phase differential which is a time domain issue, is that numerous complex physics laws are in play especially comb filtering, which is the audible effect related to phase issues.

Here is a very good and brief article from Sound on Sound addressing this
The third paragraph sort of speaks directly to this.

How do I prevent comb-filtering when close-miking?
Published in SOS February 2008
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The crack team of Paul White and Hugh Robjohns have travelled the world solving readers' problems. Here, they down the Hob Nobs and answer some of your recording queries in our Q&A mini-series, Sound Advice.

Hugh: What we're talking about here is sound arriving at different mics at different times due to the different physical distances between the sound source and the mics. Sound travels relatively slowly at around 340m/s (roughly one foot per millisecond or one metre in three milliseconds). So if you place one microphone a foot behind the other, the more distant mic will capture that sound roughly 1ms after the closer one.

Paul: In these situations, complex filtering occurs whereby some frequencies are enhanced and others attenuated, depending on the exact time difference between the two signals. A graph of such an affected waveform shows lots of sharp peaks and troughs that look not unlike the teeth of a comb (as shown below). Hence the term comb filtering is commonly applied to the phenomenon. The filter notches and peaks are strongest when the two signals are exactly the same level, and once you're familiar with the rather coloured sound that comb filtering creates, you'll always recognise it when you hear it again.



Hugh: So how can you prevent this from happening? Well, the simple answer is not to use multiple mics on the same source in the first place, and to minimise any spill from a loud sources that could reach several mics in the room. If that is not physically possible, or if you deliberately want to combine the outputs of two or more mics, then you need to be prepared to spend some time optimising the combined sound. As Paul mentioned, the comb filter effect is at its worst when the signal level from the two (or more) mics is the same. So it helps if you make one mic's contribution much less than the other's. That way you'll get some of the tonal flavour, without nasty 'phasiness'. Something more than 10dB of level difference is typically needed, although you may get away with less in some situations.

Paul: Minimising spill between microphones is also key to keeping unwanted phase effects at bay, so cardioid mics can sometimes be used in place of omnis where their directional characteristics may be exploited to reduce the amount of unwanted sound getting into the mic. Acoustic screening between microphones, where practical, will also help and, in some situations, such as with tom mics on drums, you can use gating to mute the mics' signals, so they don't contribute the mix when not being hit.

Hugh: You can also often improve the situation by time-slipping one of the microphone signals inside your DAW to re-establish time alignment. If you anticipate having to do this, it is helpful if you have a timing reference to work with on the recording. The simplest way is to record a sharp click at the start of the take a bit like the classic sync clapper board used in old film shoots. Simply tap the instrument once with something to generate a simple, clear click, wait a few seconds to make sure the reflections from that sound have died down, and start the performance. When everything is finished, it will then be easy to find that click at the start of the appropriate tracks and use it as a reference marker when time aligning the relevant tracks. Whether you slide the more distant mic track forward, or the closer one back depends on how the overall source timing works with the other tracks.

Paul: Sometimes, the precision of time slipping tracks isn't necessary or required, and a simpler approach will suffice. If you fade up two or more channels, flipping the signal polarity of one with the preamps's 'phase' button will be sufficient to confirm whether that mic's contribution is constructive to the mix or not. You will usually find that there is obviously more bass in one signal polarity than the other * you would normally select the position that provides the most bass.

Hugh: Most larger consoles incorporate a 'Phase Meter' to try to provide warning of this situation, and most DAWs will have a similar facility somewhere. Phase meters are scaled from +1, through zero and on to -1. If the two channels are perfectly time-aligned and carrying identical levels, the meter will show +1. Perfect mono! In general terms, when listening to a normal stereo mix, anything on the positive side of zero will produce acceptable mono without audible phasing problems. If the needle (or LED marker) dips below zero and stays there, you have some kind of timing/phasing problem, and listening in mono will reveal that. It's not uncommon to find the phase meter dip briefly under the zero mark especially when there are complex reverbs involved and as long as it is only a brief dip towards -1, there is probably nothing to worry about.

Published in SOS February 2008
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  #22  
Old 11-06-2011, 10:18 AM
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Kev, what I am talking about with the acoustic guitar is a related but different issue than in the link you gave. Just focusing on the guitar top, it is a spread out sound source. For example any particular place you put a mike sound from the bridge area and from the lower bout area arrive at the mike at different times and interfere with each other In addition what you have in a guitar top are Chladni patterns ( see for example http://www.bbc.co.uk/news/science-environment-13573631 ) These are somewhat semi independent sound sources. All of this arriving at the ears in a mono recording causes a phasey, or if you will, thinner sound. The neat thing is that in a stereo recording where different sounds arrive at each ear the brain interprets some of that to spacial information and it sounds better for a solo acoustic guitar, at least IMO.
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Old 11-06-2011, 12:04 PM
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Rick, hey I understand what you are saying about the guitar top and different freqz. coming from different locations on that top. And the basic psychoacoustics of stereo. Interestingly, If I remember correctly I think It was Taylor that ran some tests and determined that the lower freqz actually came off of the lower area opposite of what seems intuitive as to how the strings are arranged.

Be that as it may, it seems logical to conclude that with two mics (and all else being equal) your going to get twice the effect you mentioned "For example any particular place you put a mike sound from the bridge area and from the lower bout area arrive at the mike at different times and interfere with each other" so It would then follow that you might have the potential to have twice the comb filtering problems with two mics... But OTOH there are certainly many many great recordings of guitars done with stereo mic techniques. So there ya go

And a couple more things would then seem to make sense, that a SDC in cardioid or super cardioid narrowing the pic up pattern would then be the better option and also following this line reasoning it would seem that for instance with a single mic placing the mic further out , say more in the 3 to 6 foot range might also better address the sound board freqs differences. The Schoeps are actually considered to be quite good in this regard But then of course the more the room will come into play.
And just so were clear I am not at all opposed to the two mic techniques, in fact I used to routinely use a pair of shure KSM 44 for acoustic guitar.
One thing I have been intending on experimenting with is actually using my Schoeps in more around the 14 fret and then use my Brauner Phantom out a bit. Unfortunately I have been to busy remodeling to do any recording, but thats another story.
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  #24  
Old 11-06-2011, 12:20 PM
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Be that as it may, it seems logical to conclude that with two mics (and all else being equal) your going to get twice the effect you mentioned "For example any particular place you put a mike sound from the bridge area and from the lower bout area arrive at the mike at different times and interfere with each other" so It would then follow that you might have the potential to have twice the comb filtering problems with two mics
Like I mentioned in the earlier post, different wave patterns arriving in the two ears is reinterpreted by the brain ino spacial info, at least in part, and thus hears less of a thin phasey sound. Two exact wave patterns in each ear (i.e. mono) will not be so interpreted.
Take any of your nice solid stereo recordings, mono either channel to both ears and you will hear the phase issues I am referring to.
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Old 11-06-2011, 02:46 PM
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Like I mentioned in the earlier post, different wave patterns arriving in the two ears is reinterpreted by the brain ino spacial info, at least in part, and thus hears less of a thin phasey sound. Two exact wave patterns in each ear (i.e. mono) will not be so interpreted.
Take any of your nice solid stereo recordings, mono either channel to both ears and you will hear the phase issues I am referring to.
I will try that again, because I am married to no technique .. But if memory serves me having done this exercise a few years ago. That is going to be 1/2 of a two sided stereo recording collapsed to one side and is certainly going to sound less spacious horizontally. So the question i guess is, is that the same as a phase issue ? Actually this exercise was conducted at a studio down in LA with seven engineers present and to a man all felt that in fact that mono version was indeed clearer with less artifacts or comb filtering, while the stereo recording was fuller with a broader range of detail low to high , if minutely more smeared from comb filtering So I guess Its in the ear of the be listener.
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Old 11-06-2011, 04:11 PM
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That is going to be 1/2 of a two sided stereo recording collapsed to one side
It's 1/2 of a two sided stereo spread to both right and left channels. Regarding what other people have said about what may involve different particulars, I suggest setting up your own test, doing your own listening, and drawing your own inferences and conclusions.
Again, I am referring to a miked (no pickup) solo acoustic guitar. Voice and guitar, guitar and other instruments, or simply another instrument altogether, and you have a different ball game to consider.
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Old 11-06-2011, 05:43 PM
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Take any of your nice solid stereo recordings, mono either channel to both ears and you will hear the phase issues I am referring to.
Ok guess I was confused by the above sentence. I take it you mean send both channels or as some would say sum to mono, correct ?
And actually that is how we conducted the exercise in LA perhaps I was not clear about that or the fact that I was one of the 7 participants.

But as I said I am always willing to examine new techniques and revisit old ones because I truly believe my own sig line , for me It's the journey that really matters. Gotta get back to mixing cheers.
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Old 11-06-2011, 06:50 PM
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Ok guess I was confused by the above sentence. I take it you mean send both channels or as some would say sum to mono, correct ?
Nope, that is not what I mean. There is only one choice left.
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Old 11-06-2011, 07:13 PM
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This thread has really gone off the deep end. Didn't the OP simply aske about the how closely matched a possible 2nd km-184 would be to the one he already has?

Phase problems with a single mic? I don't think so. You might not like the results of a particular mic and or placement but that has to do with the mics performance. Interior case reflections have nothing to do with polarity. Simple cure for that - remove the grill. (Don't lose it or the screws that hold it on.) Dick Rosmini would do stuff like that all the time to see if it made any difference. Often it did and to the improvement of the sound.
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Old 11-06-2011, 08:01 PM
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Though not in the traditional sense of phase issues with multiple mikes there can be phase issues mic'ing a physically broad sound source, and one with a non uniform sound, with one mike, phase issues not in the mike but in the waveform at the mike's location. It is not the fault of the mike, just the nature of the instrument being recorded and why it is hard to get a good recording of an acoustic guitar.
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