Why Classical Stereo Techniques?

In my previous post I talk about what kind of sonic imagery is present in the piece. It is essentially stereo:

1.      The tape is in stereo, exploring depth and having a sense of width.

2.      The clarinets sit symmetrically and therefore can be captured evenly in stereo.

Capturing the piece in stereo makes sense because:

1.     Stereo techniques capture depth, to a greater or lesser extent depending on the technique.

2.      Stereo techniques capture the lateral positioning of instrumentalists, again to a greater or lesser extent depending on the technique.

Stereo techniques often come with quite fixed rules. ORTF for instance is a pair of cardioid microphones with the diaphragms 17cm apart with the capsules splayed out 110 degrees apart.

All stereo techniques can be adjusted to taste, although there are schools of thought that are more scientific about this – this is not within the scope of this research. In order to give myself a variety of options for mixing it is important to plan which techniques I will record. (n.b. I have a limit of 16 channels.) 

Some Terminology:
I don't want to assume that all the readers are audio experts so I think it is worth defining some terms that I will be using frequently: 

Term	Description	Graph
Polar Pattern	Microphones do not simply pick up sound. They accept and reject sound depending on design factors. A polar pattern is defined by how it picks up unidirectionally - or not. These patterns are then plotted onto a graph to represent a microphone model’s unique pickup characterises.	N/A
Cardioid	A polar pattern that picks up principally frontally and tends to reject sounds to the rear of the mic. These mics tend not to pick up the ambience of an acoustic very well.	Image of the the polar pattern for a microtech gefell M930 microphone. (Example 1)
Omnidirectional	A polar pattern that picks up equally right around the microphone. In practice omnis are not always strictly omnidirectional and the uni-directionality of the pick up varies by frequency. These mics tend to pick up the ambience of a room very well.	Image of the polar pattern for DPA 4006a microphone. This diagram shows how the pick-up of the microphone changes depending on the frequency of the sound (essentially, omnis tend to pick-up higher frequencies more directionally) (Example 2)
Bidirectional	A polar pattern that pick up in a figure of 8 shape. These microphones reject sounds coming from the side of the mic. These mics tend to pick up the ambience of an acoustic quite well and the side rejection can be advantageous in rooms where sounds echo (slap) between the side walls.	Image of the polar pattern for one capsule of the R88 stereo ribbon mic. (Example 3)

Which techniques and why?

Array	What is it?	Why?
Faulkner Phased Array	A 4 microphones system, using a near coincident pair and a pair of omnidirectional microphones, slightly splayed out, 66 cm apart. Mics:  Shoeps CM2 Omnidirecitonal microphones Microtech Gefell M930 cardioid microphones (possibly swap out for M950s, wide cardioids, if the bass response is poor)	This array itself allows one to adjust the balance between closeness and spacious-ness. In theory this will allow me to mix a more intimate version and a more ambient version depending on the context and relative attractiveness of the acoustic. The piece is more about depth than width. Whilst the piece is wide sounding and there is plenty of lateral movement the main spatial parameter consciously composed with is relative depth between the tape and live instruments. The ability with this array to discreetly balance the perceived depth makes this potentially an ideal stereo system.
ORTF	A two-microphone system. ORTF is one of the near coincident techniques using two cardioid microphones. In ORTF they are spaced 17cm apart and angled out 110 degrees.	In a practical sense it is a part of the Faulkner array and it makes sense to record it separately. ORTF is charaterised by clear lateral imagery but often a slightly weak bass response. Swapping the M930 cardioids for M950 wide cardioids may improve the bass response - although using wide cardioids will make this no longer an ORTF array.
AB	A two-microphone system. Microphones of any polar pattern arranged so they address straight ahead. In this case, two omnidirectional microphones spaced 66cm apart.	In a practical sense AB omnis are a part of the Faulkner array and it makes sense to record it separately. AB omnis will have a very even frequency response and excellent spaciousness, but perhaps a slightly indistinct lateral stereo image.
Decca Tree	A three microphone system: 2 parallel omnidirectionals 2m apart 1 omnidirectional centre mic 1.5m ahead of the main pair. Microphones: 2 Shoeps CM2 1 other omnidirectional microphone	The decca tree is a classic stereo technique. It captures a beautiful sense of spaciousness and may allow me to simply capture the balance in the room. It may also simply capture the tape part in the room.
Outriggers	Typically Omnidirectional microphones arranged in line with the main array(s) spaced reasonably widely (perhaps as wide as the ensemble itself). (The decca tree omnis may be spaced wide enough to replace these.)	Outriggers typically add width to a recording and a sense of ambience to a main array.
Ambient Pair	Omnidirectional microphones arranged at the rear of the hall, very widely.	Ambient mics add room resonance to a recording. I will be able to use these to add ambience to any of the main arrays.
Spot Microphones	Individual microphones for each instrument. Typically cardioid microphones.	These will be used to add detail if needed and to provide a frame of reference for the other systems.

Example 1: http://www.microtechgefell.de/index.php/en/microphones/broadcast-a-recording/large-membrane-transistor-mics/211-m930

Example 2: http://www.dpamicrophones.com/en/products.aspx?c=Item&category=234&item=24385#diagrams

Example 3: http://www.ribbonmics.com/aea/R88.html