Guidelines for a very advanced method with time alligned support microphones on a full classical orchestra. Multi-track recording techniques are mainly build up around a main stereo pair using the A-B Stereo principle. The stereo image is created from the main stereo pair and it is therefore extremely important to place the microphone pair correctly before any support microphones are set up. Guidelines for setting up an A-B Stereo pair are given in "A-B Stereo without support microphones" in this section and A-B Stereo is explained in detail in "A-B Stereo" in the section "General Stereo Microphony Techniques".

In this part the focus will be on placing and choosing the support microphones successfully and on guidelines for how to delay the support microphones to be time aligned correctly with the main stereo pair. Furthermore the focus will be on miking the instrument sections and not the individual musical instruments. Please read about the suggested microphone techniques for individual musical instrument under the relevant sections in the index.

Miking instrument sections

In order to control the different orchestra sections in the recording, it is a good idea to use directional microphones on a limited distance i.e. 1 to 1,5 meters. At these distances the loss of low frequencies due to the proximity effect will be insignificant and a first order cardioid microphone will be able to cover 3-4 musicians. The number and placement of the support microphones should be considered with respect to the -3dB points produced by the microphone's polar pattern and the law of distance to the musicians sitting off-axis to the microphone. A wide use of support microphones supplemented with relevant spot microphones for soloists will give total control of the orchestra, while a more modest number of support microphones can give the room information a higher priority in the recording.

The time alignment

If the distances from the main stereo pair to the different support microphone sections are larger than 4 meters it is a good idea to consider a time delay of the support microphones. Correct time alignment of the support microphones will preserve the timbre of the musical instruments without comb filter coloring due to phase differences between the support microphones and the main stereo pair. Furthermore a correct time alignment will be true to reflected sounds, which will give the recording important information about the room, i.e. depth, width and of cause reverberation.

The following method is developed by the Danish Broadcasting Corporation "Danmarks Radio" and is implemented in the radio concert hall "Studio 1" in Copenhagen.

Time alignment is very much dependent on the room or concert hall in which the recording is taking place. If each microphone blindly is delayed according to the distance and the speed of sound, there will be severe phasing problems if the musicians move while playing. To overcome the phasing problems while still preserving the timbre of the individual instrument the time delay has to be approximately 25% longer than the first coming sound (at the main stereo pair), calculated relatively to the first reflection (often the floor reflection). Room responses therefore needs to be measured in relevant zones, which obviously will take a lot of preparation in each new set-up or in each new location.