The Decca Tree Microphone Technique

A 1950s-era application still reigns for film-score recording

By George Petersen

This Article Features Photo Zoom

A Decca Tree in place for a scoring session at Abbey Road Studios has three Neumann M 50 mics suspended above the conductor position.

More than 50 years after its initial inception, the Decca Tree technique has become a well-established approach used in symphony halls and scoring stages worldwide. But beyond simply providing smooth capture of string ensembles, the Decca Tree offers another benefit, as well, by retaining its strong, spacious stereo imaging even after Dolby and other stereo matrixing processes.

The 1950s brought about major changes in the recording industry. The commercial development of tape recording provided a superior alternative that far exceeded the performance of disk or wire recorders, offering low-noise reproduction that was ideal for capturing the nuances of string ensembles. At the same time, blockbuster road-show releases of films such as This Is Cinerama and The Robe ushered in a new era of multichannel cinema to mass audiences, while increasing consumer interest in stereo recording led to the development of new tools and techniques suited to the task.

A vintage Neumann M 50 microphone with grill removed reveals its omnidirectional condenser capsule set into a 40mm Perspex sphere.

In 1954, a group of engineers at London's Decca Records came up with a creative solution for recording string instruments. The result, which became known as the Decca Tree technique, consisted of three microphones on a T-shaped mount with left and right mics (each about one meter from a central stem and pointed slightly downward) and a third mic in the center, about one meter in front of the other two. This configuration provided a wide stereo spread of the outer left and right microphones with the center mic's coverage eliminating any possible "hole in the middle" effect. The entire rig was centered on the group of players and placed about 10 to 15 feet above the conductor's position, forming the perfect sweet spot.

The Neumann M 50—And More
Placement is one thing, but the other aspect of the Decca Tree's success was the selection of the microphones themselves. After some experimentation with a variety of mics, the Neumann (www.neumannusa.com) M 50 was found to be ideal in this application.

Unveiled in 1951, Neumann's M 50 takes a small-diameter (12mm) omnidirectional condenser mic capsule and sets it into a 40mm molded Perspex acrylic sphere. The combination creates a mostly flat frequency response to about 1,000 Hz, but then gradually rises +4 to +5 dB above that, to a +6 dB peak from 8 kHz to 16 kHz. At the same time, the M 50 becomes increasingly directional at higher frequencies. These particular characteristics, combined with fast transient response and smooth triode-based tube electronics, made the M 50 ideal for orchestral and string recording in the Decca Tree configuration. Here, the mics have the ability to capture the upper-end nuances and harmonics of a string section, even when used at a distance from the performers, while creating a natural blend of the ensemble.

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