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Surround sound recording -- where to start?!

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Surround sound recording -- where to start?!

Postby mjfe2 » Sat Sep 28, 2013 8:35 am

I might have a chance to record an orchestra in a format that's more exciting than stereo. Where would I start with placing mics for say 5.1 and how are these usually mixed? Generally I'd stick up a Jecklin disk for orchestral work and then spots where I need them.
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Re: Surround sound recording -- where to start?!

Postby Hugh Robjohns » Sat Sep 28, 2013 9:38 am

You might find this old article series useful, and in particular, part 4:

When working in surround you have, first, to ask what kind of soundstage you desire. For classical work the vast majority put the orchestra in front and use the rear channels to convey the acoustic ambience and reverberation of the hall and audience (if applicable). In other words, they seek to place the listener in the best seat in the house.

The alternative format, which is more appropriate for pop music, in my view, is to put the listener within the musical ensemble itself -- sat where the viola or woodwind players might be -- so you might have violins and cellos in front of you, and brass and percussion behind. It can be fun, and can work well in some cases, but it can also be tiring and gimmicky.

As for the established surround mic techniques, there's nothing really new there. You still have the choice between coincident, near-coincident, and spaced mics for the main array, and often still need to use accent (spot) mics to improve the clarity and focus of some instruments some of the time.

The classic coincident surround mic array is the SoundField, used in conjunction with a 5.1 decoder -- the DSF-1 digital SoundField with the DSF-3 decoder is a stunning combination, for example. (There is also an analogue equivalent using the MkV or SPS422B SoundField mic and SP451 decoder, but it's not technically or sonically as good.)

A simpler (and cheaper) alternative is to use a double MS array which involves a normal MS pair facing forward with a second coincident directional mic facing backwards. Decoding each directional mic with the sideways fig-8 allows you to create front and rear-facing stereo images of configurable width, and the front mid mic can be fed to the centre channel.


Near-coincident options include the double ORTF array, which is exactly what it sounds like:


A similar arrangement is called the IRT or Theile Cross:


This is well suited as a distant 'space array' to capture the hall acoustics with better separation from the direct orchestral sound, and can be used in the same way as you might use s remote spaced pair to capture reverberation in a big hall.

The closest equivalent of the Jecklin disc is probably the Schoeps KFM360:


If you want to go down the spaced mic route -- as most classical does so it can take advantage of the naturalness of omnis -- then an extension of the Decca Tree is often used, such as one of the variations of the INA 5 array (eg, Brauner's ASM5):


...or the OCT or Fukada tree.


This last option is essentially a standard Decca Tree (but using cardioids to simulate the HF directionality of the M50s used in the original Decca array), with the addition of an IRT cross behind it to capture the room reverb, and some outriggers for extra spaciousness at the sides.

Monitoring 5.1 on location is a challenge, so the normal practice is to multitrack the mics and then rebalance in a studio later. The surround mic placement isn't that critical -- they really are just capturing room reverb -- but you do need to focus on the frontal mic placement to obtain the appropriate balance and perspectives... but that's no harder than working in normal stereo -- and can be judged easily enough with normal stereo monitoring.

Hope that helps.

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Re: Surround sound recording -- where to start?!

Postby illogicorp » Sat Sep 28, 2013 10:48 am

There's an interesting comparison of various surround microphone arrays here, and I believe you can also download the recordings as a DVD image:

The ORF Surround Listening Test
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