Yes, of course. The post was first of all intended as a record. But I'm willing to answer any question...
We are talking here about the different microphone arrays used in stereo recording, usually consisting of two microphones, usually of same making.
First of all the directional characteristics:
- 'omni' is an abbreviation of 'omnidirectional', meaning that it doesn't prefer any direction in space for pickup (which of course is a big simplification). Pics up a lot of the room, so not a great option in bad sounding rooms
- cardioid is a microphone with one preferred direction (again simplified).
- figure 8 is a microphone of two preferred directions lying opposite each other - literally like an eight
Now as to the different arrays usually deployed in stere recording with 2 microphones (there are techniques using more than 2 mics as well):
- AB - mostly used with a pair of 'omnis' one of them being called A and the other B - belongs to the family of so called 'spaced' arrays. It uses mostly time of arrival cues for our hearing something as Stereophonic.
- XY - mostly used with a pair of cardioids, one called X and the other Y, (and as I pointed out above depends absolutely on the mics used being directional, because here only the volume differences in different directions are providing the stereo cues) - belongs to the family of so called coincident arrays, because the diaphragms of both mics are brought together as close as possible (which has obvious limitations with real world microphones)
- MS - abbreviation of Mid-Side recording, is another 'coincident' technique deploying a pair of microphones, one of which (S - Side) by definition has to be a true Figure 8 microphone, whereas the other (M - Middle) could be of any kind. Mostly cardioids or hyper-cardioids (slightly different kind of directionality).
- Blumlein - another coincident technique deploying two figure 8 microphones crossed at 90° and with the 45° axis pointing to the center. Pics up a lot of the room sound, not so great for bad sounding rooms. Also needs a very careful placement and two relatively expensive Figure 8 microphones.
- ORTF - one of the several 'near-coincident techniques combining the advantages of coincident and spaced arrays. ORTF was developed by the French Radio and is a precisely defined arrangement of two cardioids (please do some research if you want to have more details). NOS, developed by the Dutch Radio is another one of that sort. These are easiest to realize arrays with relatively cheap microphones (though the better you can go ...)
Hope that clarifies at least the terms being used.
Here some short assessments of the different techniques.
Generally spaced and near-coincident techniques seem to deliver a more spacious and alive sound at the price of the focus and localizability of the instruments. Also the 'spread' of instruments can be tighter than real or more exaggerated (on loudspeakers).
Coincident techniques are felt as narrower, less spacious and less alive, with their advantage of having a rock solid localization and being mono compatible. There are some tricks to make coincident recordings wider and more alive, but that's already a bit of studio magic.
MS is a different animal entirely. If you just record MS to two tracks, you can't really listen to it directly, because the signal first has to undergo a transformation before it becomes a stereo signal. Some modern digital recorders have the trick on board.
The great advantage of MS is that you can change the spaciousness from fully mono to totally exaggerated space (an unpleasant sound anyway).
The mixing of MS recordings should be done on loudspeakers; it's quite difficult to properly judge it through headphones, be they as good as they may. One big disadvantage of MS is that it requires either a dedicated MS-Stereo microphone, which combined with the need for a very quiet microphone for guitar makes it expensive, or, it requires a Figure 8 microphone for the side channel, an they are very expensive if they are any good. But if you have a possibility to work with Figure 8 of decent quality for guitar recordings, that could be very satisfying.
I would say, if I had only to channels of stereo to my disposal and I would have to record a whole ensemble, I'd resort to ORTF with the two best stereo pair of cardioids I could find in my mic locker.
Recording a solo classical guitar is a very special case, because it is only one instrument, but it excites different vibrations in the whole space, so recording it just mono renders a dead and boring sound (IMHO). On the other hand you don't have the issue of representing the distances of different instruments properly in your soundstage between the loudspeakers. That's why the classical stereophonic recording arrays are not the necessarily best answer here. An ORTF pair or an AB pair could render the sound very nicely but with a spaciousness that looses focus and localization and also possibly spreads the guitar over the sound stage a bit, which feels a bit unreal.
That's why my approach would be: using an ORTF kind of an array with a third center microphone mixed to taste, making it a kind of a crossover between ORTF and MS. One also could use an AB approach with narrower spacing. Here is a lot of room for experimentation. Or do MS (see above for the disadvantage: high price).
Several tips here:
- If you record with two microphones, always pan them dead left and right, otherwise you'll have more or less phase cancellation problems resulting in unpleasant colorations of sound. If you find the array sounds too spacious, bring the microphones more together and/or turn them more inward (if cardioids).
- For XY it's almost imperative to have a matched cardioid pair
- put some time in experimenting with the positioning - the results can be different as night and day. Good idea is to find a good spot where you like to sit and play, put on a headphone and let a second person walk very very slowly in tiny increments with the microphones on a stand while you play and listen. You may find a sweet spot!
- Use the best components in your recording chain you can afford without breaking a bank - nothing is more sad than great playing drowned in the hiss and harshness of bad mics and preamps. The quality standard of even cheap equipment is not bad these days, please don't use the absolutely cheapest if you haven't to
- If you happen to record in MS technique, it's IMHO not the best idea to commit the matrixed stereo signal to 'tape'. Use the matrix only for listening back, but record the mid and the side channels on separate tracks so that you can make your spaciousness decisions later while listening to it in a relaxed mood.
Please feel free to ask more questions if you need. A lot of this stuff can be found here and there, but it's nice to have it in one spot for reference.
best wishes for your recording
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