The development of stereo reproduction happened almost simultaneously on both sides of the Atlantic in the 1930s by EMI and Bell Labs respectively. Exactly how to capture stereo information using microphones quickly developed two schools of thought, the British favouring capturing level differences between the two channels using directional mics in a "Blumlein Array" named after Alan Blumlein, who worked on early stereo recordings for EMI. The alternative, spaced pairs captured arrival time differences and was more popular in the US. Both are capable of a convincing stereo presentation when used with care. In this Heads or Tails article, Julian and James present their reasons for favouring one over the other:
Coincident Pairs - Julian
I'm not against spaced pairs, this isn't an either/or choice but I probably tend towards coincident mic arrays, though not overwhelmingly so. However, if it were a binary choice and I had to choose one over the other I would come down in favour of coincident arrays.
Why Do I Favour Coincident Pairs? - In a word, reliability. There is a difference in flavour between spaced and coincident but, while at their best, spaced pairs sound great, they are easier to get wrong.
This is usually because of mono compatibility and if mono isn't important then a lot of these issues go away but it is relatively easy to capture out of phase information using spaced pairs. It is impossible using a coincident pair at anything other than the highest of frequencies.
Not Just XY - Coincident doesn't just mean an XY pair of crossed cardioids, it can mean an M/S pair or a Blumlein array of crossed fig 8 mics - two of my favourite techniques.
Because of the nature of M/S pairs, they are very quick to set up because there is little need to match the gains between the mics when tracking, an M/S pair is, by definition, symmetrical. A Blumlein pair of quality ribbons is an amazing sound, I recently made an orchestral recording using such an array and it sounded brilliant.
Moving Sources - While placing a spaced pair of mics can be tricky, the biggest enemy of spaced pairs is movement. I'll happily use them for a piano recording, drums are fine too but players of instruments who move present the biggest problems. Acoustic guitarists, even when seated, move. Violinists are worse and though I wouldn't use a pair of mics on a violinist, I've had other, open mics within earshot of moving violinists plenty of times (an unintended, spaced array) but the worst case scenario for me has been recording an accordion. A wide instrument which is difficult to cover with one mic but with two sound sources which move as part of being played. Difficult with spaced pairs, much more stable with coincident.
Centre Image - Which brings me to my last point about coincident pairs - a solid centre image. I like the way coincident pairs sound accurate, with precise placement within the panorama. Spaced sounds lush but vague, coincident sounds more well defined.
And you only need one mic stand if you've got a stereo bar...
Spaced Pairs - James
Like Julian, I use both of the techniques that we are covering in this article. However, I think I can clarify my use of both techniques very easily. I will normally favour a coincident pair when recording distant material or for room mics. I have found that a Mid -Side paired configuration (M/S) can work fantastically as a room mic array. I will almost always use a spaced pair for closer instrument or group micing where I want a strong stereo image. This is where I feel the wide spaced pair really "wins" over a coincident pair.
Benefits Of Spaced Pairs - A spaced microphone set up will create a three-dimensional feeling in the recorded material. A well-positioned spaced pair can provide an adequate amount of decorrelation between the signals. Meaning the time it takes for a signal from the left side to get to the right side microphone will create the stereo image without too much blurring of the image or issues with phase.
Spaced techniques, in general, give a nice full sounding large sweet spot and you get a sense of an enlarged and enveloping soundstage in a larger listening field.
Drawbacks Of A Spaced Pair - The main issues with spaced pairs are the setup and tweak time. You are going to need twice as much hardware in the form of stands and cabling and then you are going to have to spend more time adjusting the distance, hight, and angle from of both mics to the performance. But get it all right and the results are well worth it.
How I Use a Spaced Pair - So how spaced is spaced? For me, it depends on the instrument in question. Most of my recording time is spent recording pop and rock bands and Drums. I will always use a spaced pair over the drums. Depending on what part of the kit I am recording, be it just overheads or maybe I am trying to get a "picture" of the kit as an entire instrument (when using a smaller number of mics). The microphones might be around 1m apart, normally about 50 cm to 1m above the highest part of the kit (normally the cymbals). The greater the distance apart the greater the hole in the centre of the image. This could have been why the "Decca Tree" configuration was created, but discussion of that technique we will save for another article.
So as stated earlier this is not an either or discussion but one of taste. The best way to find out which approach works for you is to try both and see which you prefer.
We have many articles and videos available from you to check out on this subject and we have included some of them below.