Film Orchestration - Part 4: Orchestra Recording

After we talked about Orchestra seating and differences between studios and concert halls in the past parts, it is essential to talk about how orchestras are recorded and what sort of microphone signals are used to assemble a soundtrack mix.

It should be noted that the general approach to record a concert performance and a soundtrack recording doesn't differ that much. However with soundtracks there might be occasional "experimental" setups which I will talk about later.

All orchestra recordings are based on a "main mic" signal which builds the fundament of the mix later on. Main mics are usually microphones that are placed overhead the conductor or at the axis of the conductor. Their purpose is to record the ensemble sound and basically capture the entire ensemble at a "medium distance" which would on its own create a good sounding recording of the orchestra with a proper impression of left and right and depth of the orchestra.

In film scoring the most common set up of these microphones is the so-called Decca Tree  which you can see in the upper half of the image below:

It usually consists of three microphones pointing left, center and right a few feet above the conductor. There are some rough guidelines on how far apart they should be and how they should be angled but a good engineer will adapt according to the room, the size of the ensemble and other factors.

There are other commonly used main mic setups that sometimes leave out the center mic and use different angles like ORTF and AB mic setups, but most common indeed is the Decca Tree Setup.

In standard setups there are usually a few more microphones that support the decca tree. One would be the "Out" Or "LL" and "RR" microphones which are placed usually on the same axis as the main microphone on the left and right side of the orchestra.

In the following images, these microphones are labeled LL and RR:

Their task is to capture the "outermost" signals on the left and right side so when you add them to the main mic you get a wider sound and a clearer stereo image.

In the mic setup on the two pictures above you can see some more microphones:

A and B: Their use in this case obviously was a decision by the engineer. I mentioned above that such a setup also sometimes is used as main microphones. In this case they are a little further away from the orchestra and spaced quite far apart, probably to provide a more ambient signal for the mix.

Two more microphones that are part of the standard setup are called RS and LS here which stands for Right Surround and Left Surround. They are usually placed quite far in the room or high above the orchestra to capture the room sound. They can be added to the mix to create more ambience or alternatively in a 5.1 mix be routed to the rear channels.

Additional to this set of "main mics", there are spot mics spread out in the orchestra. These are usually quite close to soloists or sections:

Their purpose is to record the details of the sound and to be used in the mix to create more presence of certain instruments when needed.

Here are two charts that illustrate the placement of mics in two different venues:

The first one is a quite reduced set-up with just a few spot mics, no surround mics and 4 Main Mics spread out at the axis of the conductor.

The second one is the setup from the photos above which captures more details. Interestingly, no close mics are placed in the Trumpets and Trombones as in most cases they are "loud enough" anyway. But many engineers do indeed record a close signal of those as well.

Up to these fundamentals, score recordings and concert recordings are relatively similar. The purpose of such a setup in general is to capture a detailed image of the orchestra with a proper field of depth and stereo field without any phasing. Phasing is a general danger with multi mic setups. With the relative slow travel speed of sound, sound from the same source might hit different microphones at slightly different times and when being played back together some of these slightly out of phase signals might cancel each other out resulting in a compromised sound. Without getting too much into detail here, usually engineers will delay compensate the individual microphones with the decca tree being the reference point. So signals that are captured with the close mics are often being delayed the amount of time it takes for the sound to travel from the instrument to the decca tree so that there will be no audible delay. Additionally, a large surface area as the one that is covered by the orchestra with a lot of influence of the room around itself is relatively forgiving regarding such problems. For instance recording a drum kit in a small room with many mics is way more problematic in this regard.

This doesn't mean that mics can just be placed anywhere. In some extreme cases, just an inch of moving the mics to a different spot might make a really strong difference of how the signal sounds. Some engineers, especially the ones who are regulars at certain studios, experiment for years to find the perfect spot for microphones (and additionally pick the right microphone which is another can of worms that I don't want to open up in this post).

In the classical world, all the signals that are recorded will be more or less leveled once and very subtly treated with any effects and then the mix is more or less "done".

In the scoring world things are a bit different.

While the basic setup of recording is similar, there is more of an "anything goes" attitude when recording scores. Especially in large studios, engineers will set up additional microphones. The most well known studio/composer for such approaches is Air Studios and Hans Zimmer, who explores every corner of that room with microphones. The technical advancement and possibility to record almost endless amounts of signals simulataneously has lead to additional mic signals that can even go to the obscure as the infamous "bottle mic" at Air. Unfortunately I couldn't find a picture of it but it is basically a microphone that is hung into a large plastic bottle and placed in the room which picks up the outside with additional resonances of the bottle.

Another factor at play is that score recordings like to isolate sections much more. You might have little booths built around the brass or percussion which of course also requires more spot mics. With recording scores in sections, this quickly adds up to several hundreds of tracks in a project, including additional sample tracks etc. Zimmer's well known mixing engineer Alan Meyerson quite often has to deal with cues that have more than 1000 tracks to sculpt a mix out of.

The liberty that all these additional microphone signals create of course are really helpful for the more "produced" sound of modern scores.

An additional factor that has come into play in recent years are 3D audio formats which also are a great playground for the music, even if it is just by capturing the room reflections from the ceiling. For this we more often see "height arrays" in recordings which are usually 4 microphones placed in a rectangle within the orchestra pointing towards the ceiling.

While the standard setup of microphones remains the same with score recordings, the line-up or individual needs of a score will require to add sometimes considerably more microphones in the room to capture everything that is required to get to the sound that is desired.

Consequentially, score mixes are a bit different than "classical" mixes. In scores, mixing engineers often use the different mic signals dynamically, with for instance some sections of the cue focussing more on the close mics and with the cue growing in size or drama slowly shifting more towards the main mics or more ambient ones.

For orchestrators who work for the scoring world, the knowledge of the recording situation might be beneficial and you can orchestrate with that knowledge in mind. This of course is again only the case if you know the studio and recording situation very well. A few general take aways are possible. For instance the obvious fact that balances within the orchestra are relatively fixed unless recorded in sections. But it is clear that you cannot alter the balance of instruments against each other drastically in the mix so that it is essential to balance it properly through orchestration.

With more specific knowledge of the recording situation you can orchestrate things a bit more strategically. One of the tricks I learned from a seasoned orchestrator is when he split out a homophonic passage that was originally written for two flutes (in this case more or less a third apart) into one flute and one oboe. When asking why he did that he said that in the studio flutes and oboes have different close mics and are relatively well separated on these signals so later on in the mix there would be more freedom to slightly change the balance of these lines against each other. It might be debatable whether this possibility outweighs the decision to change the color of this section but specific knowledge of the recording at least allows for such decisions.