Subject: Decca Tree?
From: [email-masked] (Frank Lockwood)
Date: 9 Oct 1995 13:43:16 -0400
Newsgroups: rec.audio.pro

The Decca Tree is a technique of recording that grew out of Decca's
research and development into stereo which started in 1954 with Arthur
Haddy and Kenneth Wilkinson and their team.  The first Decca stereo
products (60 records and 4 reproducers) came in 1958.

Decca has a long tradition of developing their own methods and
technology, and so they set out to develop their own method of
recording stereo as well as developing their own proprietory designs
of console and other recording equipment.

The criteria that were applied to making a good recording, as reported
by producer James Locke (quoted in:  Jim Betteridge, _Keyed to Opera_,
in _Studio Sound_, April 1987) are, in order of importance:
	1. The Musical Work
	2. The Performance
	3. The Technical Quality

The use of the three microphone technique that has come to be known as
the "Decca Tree" grew out of the desire to find a compromise between
the use of a minimal pair and the use of a multi-miking technique, in
order to maximize the clarity and depth of opera and orchestral
recordings.

The actual "tree" and the original stereo mixer were designed by Roy
Wallace.  A triangle of microphones are placed roughly ten to twelve
feet above the stage level, just behind the conductor.  There are
usually two additional flanking microphones used as well, anywhere
from either edge of the orchestra, to about one third of the way in.
The mixer is adjusted so that the centre mike goes equally to both
channels of a two track recorder, with the right tree mike and right
outrigger going to the right channel, and both left mikes to the left.

When this technique was first used in 1954, the microphones used were
Neumann KM 56s, tilted 30 degrees toward the orchestra.  Other
microphones used included the cardioid M 49 (in baffles),
omnidirectional KM 53, and finally settled in on the omnidirectional 
M50 under Kenneth Wilkinson in 1955.  The baffles used with the
cardioid microphones were four large boards fanned out from the
central point in such a way that each microphone was positioned within
its own pie wedge:

         ______________________
                   /\
                  /  \
             X   /    \   X
                /      \
               /        \
              /     X    \
                                    X = microphone

No baffles are used with the M 50 omnidirectional mikes.

The outriggers, mentioned above (additional to the Tree), also
developed to the point where the mic of choice is the M 50, facing
diagonally across the orchestra.  These mic's signals increase the
breadth and spaciousness of the stereo image.  Soloists with the
orchestra are typically spot miked.

The use of the tree has remained virtually unchanged since the '60s,
although Decca engineers have made modifications to the microphones.
In a typical Decca recording session, every effort is taken to find a
suitable recording venue with desired reverberant characteristics,
which are typically tailored by the addition of large hanging drapery
or the placement of large sheets of wood in the hall the adjust the
quality of the reflected sound.

Kenneth Wilkinson is quoted as saying (in Michael H. Gray, _The Birth
of Decca Stereo_, in _Association for Tecorded Sound Collections_,
Nov. 1987, vol. 8, no. 1, p. 7):

"You set up the Tree just slightly infront of the orchestra.  The two
outriggers, again, one in front of the first violins, that's facing
the whole orchestra, and one over the cellos.  We used to have two
mikes on the woodwind section -- they were directional mikes, 56's in
the early days.  You'd see a mike on the tympani, just to give it that
little bit of clarity, and one behind the horns.  If we had a harp,
we;d have a mike trained on the harp.  Basically, we never used too
many microphones.  I think they're using too many these days."

As for the spacing of the three mikes themselves, this varies with the
venue used and with the size of the ensemble.  For instance, when the
Montreal Symphony under Charles Dutoit is recorded in Ste. Eustache,
the centre mike is dispensed with entirely.  In chamber recordings,
the outriggers are frequently not used.  The size of the triangle
itself varies with the amount of width and spaciousness desired.

Another good source for information on this subject is an article by
Michael Gray, entitled _From the Golden Age_, that appears in _The
Absolute Sound_ magazine, Vol. 11, No. 42, pp.103 - 110.

---
             ____/      /
            /          /                    Frank Lockwood
           __/        /                Toronto, Ontario, Canada
        __/        _______