User manual AEA DECCA TREE

Audio Engineering Associates Decca Tree User's Guide · STUDIO RIBBON MICS · MIC POSITIONERS · TALL STANDS · ACCESSORIES The Decca Tree The stereo microphone array commonly referred to as the "Decca Tree" was originally conceived by the recording engineers at English Decca Records. It utilized three omnidirectional microphones situated at the ends of a large T-shaped fixture. The spacing between the left and right microphones was approximately 2 meters, and the central microphone was in front of these by about 1.5 meters. Placement of the array was generally a few feet behind and about eight to ten feet above the conductor's head. The three microphones are panned Left, Center, and Right respectively. Although it is tempting simply to aim the mics straight out from their support braces, it is preferable actually to point the principal axes of the microphones inward and downward, toward the sound source; this is because omnidirectional microphones always tend to become more directional as frequency increases. Because of the relatively close spacing of the outer microphones, the intensity cues necessary for good stereo imaging are combined with sufficient phase information to produce an open, spacious sound and, due to the middle microphone, at the same time maintain a solid central image. The Decca Tree is favored by film scoring mixers because of its ability to produce a good, stable stereo image, which will hold-up throughout the application of the Dolby and other surround-sound matrix systems. Using The Decca Tree The microphones traditionally employed were the classic Neumann M-50 large diaphragm tube condenser mics, which provided a characteristically warm and enveloping sound a sound which is still cherished by the engineers of London/ Decca Records. Other microphones, however, also are now commonly in use affording the option for different polar patterns and configurations. When considering the multitude of variations on the theme of the Decca Tree, the 1029 N. Allen Ave., Pasadena, CA 91104 www.ribbonmics.com Phone: (626) 798-9128 Fax: (626) 798-2378 first thing to try is adjusting the spacing between the microphones. The Left and Right microphones may be spaced closer or even farther apart, to change the spread of the stereo image. Similarly, the distance of the Center may be varied, relative to the two other mics. All you need to do is adjust the spacing and listen to the results. There are no hard and fast rules. In many situations, using sub-cardioid, cardioid, or bi-directional polar patterns for the Left and Right -- or even all three -- microphones might offer better focus by improving the direct-to-reverberant ratio. In this situation, aiming the mics becomes even more critical in order to avoid significant offaxis response problems. With more directional patterns, the spacing between the two side microphones generally decreases somewhat. A variation frequently employed by Ron Streicher is to use a stereo pair of microphones for the center pickup, such as an XY or MS array. When configured in this manner, the center pair provides the articulation for the stereo image, and the two outer microphones generate the spaciousness. As before, adjusting the relative levels and spacing between the microphones also will affect the overall perspective, and the final result is a matter of judgment and preference. When using the Decca Tree, or any spaced-microphone configuration, it is good practice to pay careful attention to the audio quality of the monophonic-sum of the stereo perspective. With omnidirectional microphones, it is very easy for the combined signal to result in an overabundance of reverberation (or indirect sound) for the mono listener. Also, due to the time-of-arrival (i.e. phase) differences at the microphones, some degree of comb-filtering will result. While not as noticeable when heard in stereo, these effects can seriously degrade the sound for those listening in mono. The best way to monitor this effect is by listening to the mono-sum (Left plus Right). If there is too much indirect sound or out-of phase information, it will become immediately evident by a loss of clarity and/or low-frequency information and a rather hollow or unnatural character to the sound. (Another way of checking mono-compatibility is to view the stereo signal on an XY phase display, such as the AEA LD-2020 Stereo Scope.) If the mono-compatibility is unsatisfactory, the first option is to decrease the spacing between the Left and Right microphones or to increase the signal level of the Center microphone relative to the two side mics. Selecting a different polar pattern for the microphones is another option. Relocating the entire array closer into the sound source also should be considered, particularly if there is an excess of reverberant information. Picture 1. Decca Tree using three 1 meter bars The AEA Decca Tree System Audio Engineering Associates has developed a modular system for configuring Decca Tree arrays. This utilizes our SMP Stereo Microphone Positioners with a central mounting bracket assembly. With our SMP-17 (seventeen inch), SMP-1M (one meter) and SMP-1.25M (1.25 meters) bars, several variations are possible. See the comprehensive document "Modular Microphone Positioning Systems: Stereo Bars and Decca Trees" for more information about modularity. The Mini Decca Tree: one SMP-1M (or SMP-1.25M) bar for the sides and a SMP-17 for the center, configured using our Mini Tree Bracket; this array is very useful for smaller ensembles or when a stereo pair serves as the center pickup. Of course, any combination of SMP bars and Decca Tree Brackets may be configured for other arrays. Additional sliders for the SMP's also may be employed when additional microphones are added to the array. The Decca Tree may be suspended from the holes at the end of the three SMP Bars, or stand-mounted using one Slider (with the female stand-coupler) on the forward bar. For maximum strength when the array is stand mounted, we recommend that all of the bars be set on top of the Bracket so that it will form a supporting base for the complete assembly. The microphones may be located as desired along the three SMP Bars -- Left, Center, and Right. When stand-mounted, be sure to position the microphone stand support Slider so that the entire array, including the microphones, is properly balanced. Whenever possible, we also recommend that the microphones be mounted below the SMP bars (i.e. hanging downward). This will minimize the tendency for the entire array to tip or rotate due to the natural effects of gravity. As with all stand-mounted microphones, it is good practice to use shockmount suspensions to attach the microphones to the Decca Tree assembly. We also recommend that the entire array be additionally isolated from the support stand using the AEA Floater shock-mount assembly. This heavy-duty unit will further reduce mechanical noise by decoupling the entire array from the microphone stand. Picture 2. MiniDecca Tree using one 17 inch bar and one 1 meter bar Other Products by Audio Engineering Associates: AEA Stereo Template Less expensive stereo bar designed for mounting Coles in ORTF and Blumlein configurations. The AEA TRP Ribbon Preamp A ribbon preamp designed for ribbon mics with ultra quiet circuitry boasting 83dB of clean gain, and no phantom power. AEA Ribbon Microphones R84 - Studio Ribbon Mic R88 - Stereo Ribbon Mic R92 - Studio Ribbon Mic specifically designed for close micing and guitar RCA Working Reproduction Microphones and replacement parts AEA R44C Microphone - Museum Quality Reproduction Our tribute to the classic RCA 44B using New Old Stock ribbon material AEA 44CX Microphone 6db more output for critical digital recordings AEA 44CNE Microphone Based on RCA LTD production - the same sound but easier to build Modular Studio Microphone Stands and Booms Coles Microphones Since 1983 we have imported and serviced the Coles 4038 studio ribbon microphone and the 4104B, "lip" mic for voice-over work in high noise environments. We sell and service the mics and stock replacement parts. CB Electronics In North America we also represent CB Electronics, a leading worldwide supplier of machine control equipment to the sound-for-picture industry. Their products specialize in professional control of and translation between bi-phase, 9-pin serial and time code machines. Their SR line provides low cost multiple machine remote controls for RS-422, Sony, and Tascam DA88 proto col machines. 1029 N. Allen Ave. Pasadena, CA 91104 Phone: (626) 798-9128 Fax: (626) 798-2378 www.ribbonmics.com Audio Engineering Associates · STUDIO RIBBON MICS · MIC POSITIONERS · TALL STANDS · ACCESSORIES