It was originally developed as a sort of stereo A–B recording method adding a center fill. The technique was developed in the early 1950s and first commercially used in 1954 by Arthur Haddy, Roy Wallace, and later refined by engineer Kenneth Wilkinson, and his team at Decca Records, to provide a strong stereo image.
A Decca Tree setup uses five omnidirectional microphones, three arranged in a "T" pattern, and an outrigger pair further to the left and right. The stem of the T faces the orchestra, and the microphones on the crossbar of the T are placed about 5 feet apart. The centre microphone is placed 2.5 feet out. Former Decca engineer John Pellowe describes the specifics of the setup as follows:
Well we used to have a thing called a Decca tree which was an arrangement where [at] the front edge of an orchestra about 3.2 metres up in the sky you would have a centre microphone roughly in line with the edge of the orchestra, and then maybe 2.5 feet back and 5 feet apart you would have 2 more forming a triangle, omnidirectional microphones. These were Neumann [m50’s] I’m talking about...
The centre microphone would be looking right into the centre of the strings in front of the conductor. You would have the conductor out front, then there would be a couple of desks of strings before you get to the woodwinds, and we would be looking right into the centre of those strings with that microphone. Then we would have the [rear] two, the left and right [mics on the] tree, which would again be looking right into the first violins and the celli, if that was the way the orchestra was set out, and then we would have a couple of outriggers which were maybe twenty feet apart 3.2 metres high again, 10 foot 6, and they again would be omnidirectional... 5 feet away from the edge of the orchestra 10’6” high looking down into the strings. ... it was a very controversial method of recording, because when you have that many spaced omnidirectional microphones you lose a lot of the directional cues, which is absolutely right, the way that we would deal with that was we would pan the left and right tree half left and half right, and the outrigger mics we would pan hard left and right and we would paint an artificial stereo image... the reason we did this and consistently did it and got away with it and got wonderful reviews and many many awards was simply that the localisation cues were missing, but the sound was fantastic.
The reason that the Decca system survived as long as it did was that it was comparatively adaptable to different acoustic spaces. It was comparatively easy to auto-balance it and you didn’t have to fiddle with it much, generally speaking in order to make it reliable.
The Decca Tree was originally used in orchestral situations, fitted on a tall boom and suspended in the air, roughly above the conductor.
The technique traditionally uses three omnidirectional microphones, traditionally of the Neumann M-50 small-diaphragm pressure transducer tube condenser type, to record in stereo. These microphones are not truly omnidirectional at the higher frequences, but exhibit some high frequency lift and directionality which is likely to positively affect stereo imaging of the Decca Tree arrangement. Variations have been performed using a coincident pair, in X-Y, Mid/Side (M/S), or Blumlein positioning, in place of the center microphone. The Neumann M49, Km 53, and KM 56 were also evaluated and used for early sessions by the Decca team, and later the Schoeps mk2S were used by the team for live productions where the m50 proved too cumbersome.
The Decca Tree is a great sounding stereo miking technique often used in large orchestral or choir performances, but it can also be used as a room miking technique for recordings. When used for room miking drums, its wide stereo image captures the nuances of bigger environments better than most other techniques. In smaller rooms however, the Decca Tree does not work as well.
Ron Streicher, author of "The Decca Tree — It's not just for stereo any more" has also described methods for employing a Decca Tree for surround recording. He utilizes a SoundField MK-V for the center, a pair of Schoeps MK21 sub-cardioid condensers for the left and right, and a pair of Schoeps MK41 hypercardioid condensers for the left and right surrounds. The MK-V affords a number of possibilities to the Decca Tree, as it is a four-element transducer that can be decoded into 5.1 and 7.1 sound fields on its own, using the SoundField SP451.
- Decca Tree Recording with Georg Neumann pressure microphones M 50 - in German — pdf
- The Decca Tree — A classic microphone placement system of the 1950s
- "The Decca Tree — It's not just for stereo any more" (PDF)
- A Decca Tree primer — Wes Dooley, Audio Engineering Associates AEA — pdf
- Stereo Bars and Decca Trees — Wes Dooley, Audio Engineering Associates AEA — pdf