Recording an orchestra: main pair, outriggers and spots
An orchestra recording typically builds a picture from several layers: a main stereo microphone system, a pair of outriggers, and spot microphones for individual sections. The main system carries the stereo image and the room. The other layers refine it.
The main system
Usually a stereo pair or a Decca tree, placed above and slightly behind the conductor, 3 to 4 m above the floor. The recording angle of the system should match the angle that the orchestra covers when seen from there. Moving the system back makes the orchestra look smaller; moving it forward makes it fill more of the picture.
Outriggers
A spaced pair of omnidirectional microphones to the left and right of the main system, panned fully left and right. They widen the image and give the outer string sections a presence that a central pair cannot reach.
Spot microphones
Spot (or support) microphones are placed close to sections that need help: woodwinds, harp, timpani, solo instruments, double basses. They bring clarity and balance, but they come with side effects:
- Their sound arrives earlier than the same sound at the main pair. Without correction, the spot microphone's position determines the localisation of that source (precedence effect).
- They add close, dry sound that does not match the room.
Delay them
Delay each spot microphone by the difference in travel time: the path from the source to the main pair minus the path from the source to the spot microphone, divided by the speed of sound.
delay = (source-to-main distance − source-to-spot distance) / c
| Source to main pair | Source to spot | Delay |
|---|---|---|
| 6 m | 1 m | 14.6 ms |
| 8 m | 1 m | 20.4 ms |
| 10 m | 0.5 m | 27.7 ms |
| 15 m | 1 m | 40.8 ms |
At 343 m/s, each metre of path difference is about 2.9 ms. With the delay set, the spot signal lines up with the same sound in the main pair, the main pair determines the position, and the spot adds clarity only. Some engineers add a few extra milliseconds on top so that the main pair is clearly first (precedence effect); treat that as a separate, deliberate choice rather than part of the alignment. Compute the delay with the delay and distance tool.
Level
Raise the spot microphone just until you notice the effect, then lower it a little. If you can hear it as a separate source, it is too loud. Combining two signals of the same source at different levels follows the usual addition rules, see Adding levels correctly.
Pan
Pan the spot microphone to the position of the source in the main pair's image, not just according to the stage plan.
Common mistakes
- Using too many spots, which turns the picture into a close-miked mix.
- Forgetting to delay them.
- Placing spots so that they pick up more of other sections than their own, which causes comb filtering, see Comb filtering.
Draft: written by an AI assistant, awaiting technical review.
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