Orchestral recording basics

It is generally better to use a stereo main microphone rather than trying to use a multimicrophone setup, because you need to mix everything down while recording and you can only use headphones for monitoring. It takes a lot of experience to get a good mix using headphones.
If you are recording to two-track, using a good sounding main microphone pair or a main stereo microphone should be your first choice.
Try to get the soloists to play in front of the orchestra so their sounds will not be drowned out by the orchestra and you will get a well-balanced recording. This also improves the communication between the conductor and the soloists.

Recording locations may be anything from dry to extremely reverberant, so we would like to suggest three different microphone setups. Also, remember that you should select your microphones to match the acoustics of the recording room.

ORTF technique (for more reverberant rooms)

Mount two cardioid mics (AKG C 480 B + CK 61 or C 391 B) on a short stereo bar, angling each 55° off axis (110° between the two mics), making sure the distance between the capsules (the centers of the two diaphragms) is 17 cm (6.7 in.).

Place the microphone pair about 2 to 2.5 meters (6 1/2 to 8 feet) higher than the floor of the performance area (where the orchestra sits), about 1.25 to 2.00 meters (4 to 6 1/2 feet) behind the conductor. If the floor of the audience area is higher or lower than the performance area you'd have to deduct or add the difference in height. Slightly point the whole array about 5° down.
Listen carefully to the results and adjust working distance and height until you are satisfied.
This miking technique will reduce the amount of ambience in your recording and provides good imaging.

The Decca Tree (for good sounding rooms with short reverberation times)

Use 3 omnidirectional Mics (C 480B + CK 62). You will have to mix the three mics down to two tracks, which is not very difficult. Set the L and R microphones to unity gain and the center mic to -5 dB to -10 dB. Listen carefully, you should not be able to hear the center mic, but you shouldn't get the impression of a "hole in the center" either.

Place the center microphone right behind the conductor, and make sure all microphones are about 1.8 to 2 meters (6 to 6 1/2 feet) above the performance area floor.
As omnis are not omnidirectional at all frequencies but tend to approximate a cardioid at higher frequencies, point them at the orchestra/choir (not as shown in the picture!).
This array will pick up much more reverberation and provide a recording with beautiful ambience. If you don't have enough space for one of the two setups described above, try the

XY technique

Mount two cardioid microphones (similarly to the ORTF technique) on a stereo bar, angle them 90° angle as shown above, with the capsules of the two mics above (just short of touching) each other.

Place the setup right behind the conductor 2 meters (6 to 6 1/2 feet) above the performance area floor, pointing 5° down. This will give you less ambience in the recording and you may have to add some artificial reverberation later on.

As mentioned before, this can only give you a basic idea of correct recording, as there is no out-of-the-box solution that suits every situation.
Our final suggestion is probably the most important: Take your time, listen, listen again, and do not be ashamed to move your mics during rehearsals. Experiment until you get the best sound!
As for peaks: During rehearsals, set your recording levels at - 6 dBfS (6 dB below maximum) for the loudest passages. This will leave you enough headroom for the performance recording. (Experience shows that musicians and singers are louder during the actual performance than they were during the rehearsals.)

By Georg Burdicek