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Decca tree

The Decca Tree is a pioneering microphone technique developed in 1954 by engineers Roy Wallace and Arthur Haddy at the Decca Recording Company in , designed primarily for capturing the full spatial depth and balance of orchestral performances using a simple array of three microphones suspended above the conductor's . This setup evolved from early experiments in the 1950s amid the emergence of stereo recording formats, initially employing Neumann M49 cardioid microphones on a T-shaped steel bar to address the challenges of phase coherence and mono compatibility in orchestral captures. Later refinements by recording engineer Kenneth Wilkinson in the 1960s standardized the configuration with Neumann M50 omnidirectional microphones—known for their pressure response and spherical design that enhances directionality above 1 kHz—arranged in an isosceles triangle: the left and right microphones spaced approximately 2 meters (6.5 feet) apart, and the center microphone positioned 1.5 meters forward, all elevated 2.5 to 3 meters (8 to 10 feet) high. Optional outrigger microphones, placed 3 meters to the left and right at the same height, were sometimes added to widen the stereo image without introducing excessive phase issues. In practice, the left and right microphones are panned hard left and right, respectively, while the center feed is split equally to both channels, producing a warm, enveloping sound with excellent localization of instruments and natural , particularly suited to venues like London's Kingsway Hall. This approach prioritized over multi-miking, avoiding comb filtering and ensuring seamless transitions to mono playback, which was crucial in the pre-digital era. The Decca Tree's influence extends beyond , becoming a staple in , , and even modern pop recordings, with contemporary adaptations using microphones like DPA 4006 or Schoeps 2 for similar capture while maintaining its core philosophy of capturing acoustic reality with fidelity. Its enduring legacy lies in democratizing high-quality stereo imaging, influencing recording standards at studios like and remaining a benchmark for immersive audio techniques today.

History and Development

Origins at

In the , established itself as a pioneer in high-fidelity recordings, emphasizing natural sound reproduction and orchestral balance through innovative engineering practices. Building on its earlier full frequency range recording (ffrr) system introduced in the 1940s, Decca focused on capturing the full dynamic and tonal range of symphonic performances, particularly with British orchestras in venues like Kingsway Hall. This commitment drove the label's technical advancements during a period when the recording industry was shifting from to stereophonic formats, aiming to preserve spatial depth and instrument separation in orchestral settings. As the transition to gained momentum in the early 1950s, Decca engineers began experimenting with spaced arrays to address the limitations of single-point mono techniques, seeking to enhance and the sense of orchestral width without compromising coherence. These efforts culminated in the development of the Decca Tree around 1954, a configuration named after the label and designed specifically for classical ensembles to achieve immersive spatial representation. The technique emerged from initial stereo trials, including an experimental session on December 23, 1953, and was first implemented commercially in March 1954 for a recording by engineers Roy Wallace and Arthur Haddy. The Decca Tree quickly became integral to Decca's landmark classical recordings, contributing to the label's renowned "Decca Sound" in stereo releases from the mid-1950s onward, such as those featuring the London Philharmonic Orchestra under conductors like , including early stereo releases like Handel's in 1955. By prioritizing a simple T-shaped array suspended above the orchestra, the method facilitated natural that became a hallmark of Decca's classical catalog during this era.

Key Innovators and Timeline

The Decca Tree microphone technique was primarily developed by engineer Roy Wallace at , who designed the initial setup in 1954 using three M49 cardioid s mounted on a T-shaped bar to capture orchestral . Arthur Haddy, head of Decca's recording operations, contributed to the early research by evaluating venue acoustics and overseeing the transition to experimentation, while Kenneth Wilkinson, a senior balance engineer, later refined the configuration in the late 1950s by incorporating microphones for enhanced width and phase coherence. These innovations built on Alan Blumlein's foundational work in recording techniques, such as the coincident pair, but the Decca Tree's distinctive three- spaced array addressed common pitfalls like the "hole-in-the-middle" effect—where central sounds appeared weak—by positioning a forward center to blend seamlessly with the outer pair. The technique's timeline began with its assembly and first practical tests in 1954 at Decca's London studios, marking an internal shift from mono to stereo amid the company's emphasis on classical recordings. By 1958, it saw application during sessions in venues like Vienna's Sofiensaal, where Wallace's setup was used for orchestral works such as Robert Stolz waltzes. Through the late 1950s, refinements introduced Neumann KM56 microphones and later standardized on Neumann M50 omnidirectional models, with microphone spacing adjusted closer over time to improve phase alignment and reduce comb filtering, culminating in uses like Benjamin Britten's Peter Grimes in 1958 using a KM56 Tree with M50 outriggers. Although no formal patents were filed for the Decca Tree itself, the technique remained a closely guarded proprietary method within until the early 1960s, relying on custom-built consoles and internal documentation to maintain its edge in high-fidelity classical production. This secrecy underscored Decca's engineering team's collaborative expertise, with Wallace's standalone tree philosophy complementing Wilkinson's hybrid approaches to achieve the label's renowned spatial depth.

Technical Configuration

Microphone Arrangement

The Decca Tree employs a basic configuration of three arranged in a T-shaped that outlines a triangle, with dedicated left, center, and right positions to capture a wide image. This geometric setup positions the center forward relative to the left and right pair, ensuring balanced coverage of the sound source. In electrical mixing, the center microphone signal is typically blended equally into both the left and right channels to eliminate any perceived hole in the stereo center, while the left and right microphones are panned hard to their respective sides for maximum width. This approach enhances the overall coherence without requiring additional processing during recording. The microphones are mounted on a horizontal T-bar or boom, which provides rigid support and precise spacing, and is suspended overhead above the conductor or primary sound source to optimize perspective. To address phase considerations inherent in spaced microphone arrays, identical microphone models are emphasized across the three positions, promoting uniform frequency response and minimizing comb filtering effects that could arise from inter-microphone spacing and time-of-arrival differences. Mono compatibility checks during setup further help mitigate potential phase cancellations.

Positioning Guidelines

The Decca Tree is typically positioned at a height of 2.5 to 3 meters (8 to 10 feet) above the conductor's head to capture a balanced of the while minimizing phase issues from below-stage reflections. This elevation allows the microphones to envelop the sound source evenly, with the array positioned above the conductor's podium to capture the from the front while blending direct and ambient sound. The spacing between the left and right in the main is generally 1.5 to 3 to achieve optimal width without compromising mono compatibility or introducing excessive time differences that could blur the image. The center is offset approximately 1 to 1.5 forward of this pair, forming a T-shaped or isosceles triangular configuration that enhances . For extended setups, are placed 3 to 6 to the left and right of the main array's center, aligned at the same height and often in line with the rear pair, to widen the field for broader ensembles. In reverberant halls, placement guidelines emphasize positioning the tree slightly farther forward and higher within the venue to harness natural reverb for a of , while avoiding excessive distance that could introduce unwanted blur or in the low frequencies. Engineers adjust the array's proximity to reflective surfaces to capture controlled ambiance that supports the orchestra's transient clarity without overemphasizing decay tails. Adjustments for ensemble size involve scaling the overall setup proportionally: for full symphonies, wider spacing (up to 3 meters between main mics) and outriggers are employed to encompass the expanded soundstage, whereas smaller chamber groups or reduced orchestras use tighter configurations (1.5 to 2 meters spacing) positioned closer overhead to maintain intimacy and focus. This scalability ensures the tree adapts to varying stage footprints, with height potentially reduced to 2 meters for compact setups in drier acoustics.

Microphones and Equipment

Preferred Omnidirectional Types

The Decca Tree technique relies on microphones to achieve uniform pickup across the orchestral stage, capturing a natural and spacious image without directional bias. This pattern ensures even sensitivity to sources from all angles, preserving the acoustic ambiance of large ensembles in classical recordings. Ideal microphones for the Decca Tree exhibit a flat from 20 Hz to 20 kHz, allowing faithful reproduction of the full in orchestral music, from deep to high harmonics in strings and woodwinds. Additionally, low self-noise levels, typically below 15 (A), are essential to handle the subtle and quiet passages common in classical without introducing audible hiss. Classic choices at Decca included tube-based models such as the M49, set to its cardioid pattern in early stereo orchestral sessions for its warm, detailed capture. The KM56, a compact tube , was prized for its clarity in early implementations. Later refinements standardized the M50 —known for its pressure-gradient response and spherical design that enhances directionality above 1 kHz—as the preferred option, offering transparent sound with minimal coloration. As solid-state technology emerged, the Schoeps MK 2 capsule became a favored choice, providing a extending to 28 kHz when paired with compatible preamplifiers. For optimal performance, in a Decca Tree must be matched in and impedance, often as factory-paired sets, to ensure balanced output levels across the three positions and prevent phase inconsistencies in the mix. This matching is critical for maintaining , with variations as small as 1 dB potentially disrupting the array's coherence.

Common Alternatives and Substitutions

When preferred , such as the classic Neumann M50, are unavailable due to their vintage status and high cost, engineers often turn to budget-friendly substitutes that approximate the desired response and natural tonal balance. The AKG C12 VR, a modern reissue of tube , can be configured in mode to serve as an effective stand-in, offering a warm, detailed sound suitable for orchestral capture in Decca tree arrays. Similarly, the Rode NT2000, a versatile multi-pattern , provides an accessible option with solid low-end extension and clarity when set to , making it viable for smaller-scale or entry-level Decca tree implementations despite its more pronounced proximity effect compared to dedicated omnis. For contemporary high-end applications, microphones like the DPA 4006 and Josephson C617 have gained acclaim for their exceptional transparency and low self-noise in Decca tree configurations, closely emulating the spacious, uncolored imaging of historical setups. The DPA 4006A, with its ultra-linear and minimal coloration, is frequently deployed in orchestral recordings to deliver precise and ambient detail without the need for extensive processing. The Josephson C617, featuring a pure diaphragm for neutrality, is similarly praised for maintaining phase coherence across the array, enhancing the technique's signature depth in modern classical productions. In scenarios requiring adjustments for closer miking or enhanced directivity, cardioid outriggers are occasionally substituted for traditional ones, though this is rare in pure Decca tree applications due to potential disruptions in and phase alignment. Such tweaks, as seen in variations like the Fukada Tree, use cardioids in the main array with omni outriggers to balance focus and ambience, but engineers note caveats including reduced width and possible comb filtering when deviating from omnis. Vintage microphones like the ELA M 251, valued for their lush mode in classical contexts, face availability challenges owing to rarity and maintenance issues with original tubes and capsules. Today, these are often emulated through high-fidelity replicas such as 's own ELA M 251E reissue, which recreates the original's smooth highs and warmth using updated components, or via digital plugins like Universal Audio's emulation for modeling in DAWs.

Applications in Recording

Orchestral and Classical Music

The Decca Tree has been a cornerstone for capturing the spatial depth and cohesion in orchestral and recordings since its development in the mid-1950s. Positioned approximately 3 meters above the conductor's , the array's three primary s—typically arranged in an with left and right elements spaced 2 to 3 meters apart—create a wide image that mirrors the orchestra's layout. This configuration allows for clear separation of instrumental sections, with the left microphone emphasizing strings and woodwinds on stage left, the right capturing brass and percussion on stage right, while the forward center microphone anchors the overall balance and highlights soloists or the conductor's focal point. In practice, this excels in symphonic works, providing a natural sense of width and depth that preserves the orchestra's antiphonal effects, such as the call-and-response between string and brass sections in large-scale pieces. The technique's mono compatibility ensures the recording translates well across playback systems, a critical consideration for classical releases intended for both home listening and broadcast. Engineers like Kenneth Wilkinson refined the setup during Decca's golden era, adjusting microphone angles (often 30 degrees inward) to enhance localization without phase issues, resulting in recordings that convey the live hall experience with remarkable fidelity. Prominent examples from the 1950s and 1960s showcase the Decca Tree's impact on classical discography, including Georg Solti's recording of Wagner's Der Ring des Nibelungen with the Vienna Philharmonic (Decca, 1965–1970), which utilized the technique to capture the epic scale and orchestral detail. These recordings, part of Decca's broader symphonic output during the period, established benchmarks for stereo classical production, influencing subsequent generations of engineers. To achieve precise balance in complex ensembles, the Decca Tree serves as the primary array, augmented by selective spot microphones for individual sections or solo instruments. Close-placed cardioid or spot mics—often on principal strings, woodwinds, horns, , and —are blended at low levels (typically 10-20% of the mix) to reinforce detail without disrupting the Tree's cohesive image. This hybrid approach, pioneered by Decca engineers, allows for subtle corrections in perspective, such as boosting a solo or without altering the overall orchestral blend, ensuring the recording retains a natural, unamplified quality. The technique thrives in acoustically favorable venues that provide natural reverb, with Kingsway Hall in serving as Decca's primary location from the through the . The hall's domed ceiling and resonant wooden interior delivered a warm, enveloping ambience, ideal for the Decca Tree's capture, which integrates the orchestra's direct sound with the space's reflective qualities. Recordings made there benefited from this synergy, producing a sense of grandeur and immersion that artificial reverb could not replicate.

Adaptations for Other Genres

In jazz and chamber music recordings, the Decca Tree configuration is often scaled down to accommodate smaller ensembles and more intimate spaces, reducing microphone spacing to approximately 2 meters between the left and right omnis while positioning the center microphone about 1.5 meters forward to maintain balance without overwhelming the natural dynamics of the performers. This adaptation preserves the technique's spacious stereo imaging but minimizes phase issues and excessive room sound, making it suitable for capturing acoustic instruments like piano, guitar, or percussion in closer proximity. For and film scoring, the Decca Tree has been integrated into hybrid setups that blend orchestral elements with contemporary production, particularly at studios like where it supports soundtrack recordings by providing a wide, mono-compatible foundation for strings and ensembles. In film scoring, engineers frequently employ the standard three-microphone array with Neumann M50 omnis for main capture, adding outriggers or spot mics to enhance clarity in large scoring stages, as seen in orchestral sessions for scores like those in The Lord of the Rings. Modern pop applications extend this to mixes, where the Tree forms the frontal triplet in immersive arrays. Adaptations for live versus studio environments involve height and positioning adjustments to account for stage monitoring and hall acoustics, with the Tree suspended higher in concert venues to reduce direct bleed from monitors while incorporating additional omnis to capture controlled reverb without muddiness. In studio settings, the array is lowered closer to the source for drier, more defined imaging, whereas live concert hall recordings leverage the natural reverberation by widening the spacing slightly to emphasize spatial depth. In the 2020s, the Decca Tree has seen renewed use in spatial audio for ambient recordings and scores, often expanded to a "Decca Tree-3D" variant with height channels for immersive formats like 7.1.4, enabling VR-compatible captures in and gaming applications that require 360-degree soundscapes. This setup, using microphones with spheres, supports ambient electronic or orchestral elements in soundtracks by providing natural room integration and object-based positioning for platforms like .

Advantages and Limitations

Key Benefits

The Decca Tree technique excels in delivering a natural sense of depth and width in recordings, achieved through the spaced arrangement of that capture the orchestra's spatial layout without relying on artificial panning or post-processing. This configuration immerses listeners in a realistic soundstage, mimicking the live hall experience by preserving the ensemble's inherent positioning and . A key strength lies in its coherence and accuracy, where the central microphone blends seamlessly with the outer pair to minimize comb-filtering effects and ensure robust , outperforming simple spaced-pair setups that often suffer from cancellation when summed to mono. This three- blending maintains across playback formats, making it particularly reliable for broadcast and archival purposes in production. The technique's simplicity in setup is another major advantage, requiring only a minimal number of microphones mounted on a T-shaped bar suspended above the , which enables efficient capture of an entire in live-to-two-track sessions without extensive spotting or complex arrays. This streamlined approach reduces preparation time and logistical demands, ideal for venues with limited access or time constraints. Finally, the Decca Tree contributes to a timeless sound quality that has defined classical releases, faithfully preserving the hall's natural ambiance and warmth to create recordings with enduring spatial richness and emotional depth. Its emphasis on capture avoids coloration, resulting in a spacious, uncolored that highlights the acoustic nuances of performance spaces.

Potential Drawbacks

The Decca Tree microphone technique exhibits significant sensitivity to the acoustics of the recording environment. In dry or dead spaces, the microphones fail to capture sufficient natural , resulting in a sterile or unnatural orchestral image. Conversely, in overly reverberant venues, the omnis pick up excessive room reflections, often leading to muddiness and blurred transients that compromise clarity. This dependence on ideal acoustics limits its effectiveness in non-optimal settings, such as smaller or untreated rooms. Achieving precise balance among orchestral sections poses another challenge with the Decca Tree. The spaced array captures an overall soundfield but struggles to isolate individual instrument groups evenly, particularly for quieter or positioned-off-center sections like violas or woodwinds, risking uneven levels without the addition of spot microphones. Misplacement of the tree can exacerbate this, causing some sections to dominate or recede in the mix, demanding meticulous adjustments during setup. In modern contexts, the technique can encounter pitfalls related to phase coherence, with comb filtering artifacts arising from time-of-arrival differences between the spaced , especially if spacing deviates from precise guidelines (typically 1.5–2 meters), manifesting as hollow or notched frequencies in the stereo image when summed to mono. The Decca Tree's dependence on premium omnidirectional microphones, such as the M50 (vintage models priced around $29,000 each as of 2025), contributes to its high cost and relative rarity outside major studios. Custom T-bars for mounting add further expense (around $750 in the early ), rendering the setup inaccessible for budget-conscious engineers or small facilities that lack access to such specialized, often vintage equipment.

References

  1. [1]
    The Decca Tree | The Secrets Behind This Technique
    Aug 9, 2021 · It was devised and assembled for the first time in 1954 by Decca Recording Company´s engineers Roy Wallace and Arthur Haddy. The first version ...
  2. [2]
    Microphones: The Decca Tree Technique - Tape Op
    History. In the 1950s, stereo was an emerging format. · In Use. The left and right mics are spaced two meters apart (about six and a half feet), and the center ...
  3. [3]
    How the Decca Tree Grew - AudioTechnology
    Feb 19, 2012 · The original trees back in '54 and '55 used Neumann M50s with a variety of baffles. The microphones were positioned close together so the ...
  4. [4]
    A Look At The Decca Tree Stereo Recording Technique
    The Decca Tree, the standard for orchestral recording, comprised of a spaced pair with a center mic connected to a custom stand and suspended over the ...
  5. [5]
    The Decca Tree - PS Audio
    Sep 14, 2022 · The classic Decca Tree setup uses three omnidirectional microphones ... hole in the middle" in their imaging; it points the sound source.
  6. [6]
    Revisiting The Crystal Clarity Created By The 'Decca Sound ... - KCUR
    May 26, 2015 · A new 53-disc CD box called "Decca Sound" celebrates the history of Decca's pre-stereo recordings from the early 1950s. It was just around this ...
  7. [7]
    Decca Records: A History Of 'The Supreme Record Company'
    By the late 50s, Decca had rolled out Full Frequency Stereophonic Sound (FFSS), and, with John Culshaw now heading up the technical advances, Haddy and his ...Missing: 1950s | Show results with:1950s
  8. [8]
    Guide to collecting - Decca | Spiral Classics
    Decca started issuing LPs in 1950, and started issuing Stereo LPs in 1958. They produced some of the finest stereo LPs, and many collectors particularly value ...
  9. [9]
    The Decca Tree - Mixonline
    Sep 1, 2003 · We can trace its origins to March of 1954, when engineers RoyWallace and Arthur Haddy at the Decca Studios in London prepared for arecording ...
  10. [10]
    Decca tree - DPA Microphones
    A stereo microphone technique developed by Roy Wallace and Arthur Haddy at Decca Studios in London in the 1950s, most used for orchestral recordings.
  11. [11]
    Belated RIP: Roy Wallace, Inventor of the Decca Tree - AllMusic
    Nov 14, 2007 · Wallace first brought out the "Decca Tree" at Decca's first experimental stereo session, held December 23, 1953, attaching three Neumann M49's ...Missing: Philharmonic | Show results with:Philharmonic
  12. [12]
  13. [13]
  14. [14]
  15. [15]
    Untitled
    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, Kenneth ...Missing: history key innovators timeline
  16. [16]
    [PDF] AEA Decca Tree ManualC (WP) - OpusKlassiek
    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 ...
  17. [17]
    Decca Tree / SB-DT - Grace Design
    Out of stockThese are configured to provide a 2 meter spacing between left and right microphones and a center microphone 1 meter forward. Since the stand mount adapter can ...
  18. [18]
    Immersive/object-based audio recording techniques
    Choosing five identical microphones instead of just a specific microphone ... The Fukada Tree is a Decca Tree array, but with five cardioid microphones ...
  19. [19]
    MK 2 | Microphone capsule - SCHOEPS Mikrofone
    Rating 5.0 (1) Technical Specifications ; Maximum sound pressure level (THD < 0.5 %). 130 dB-SPL with CMC 6 134 dB-SPL with CMC 1 ; Length. 22 mm ; Diameter. 20 mm ; Weight. 17 g.
  20. [20]
    Complete Set for Recording with a Decca Tree - SCHOEPS Mikrofone
    The Decca Tree is a triangular arrangement of three omnidirectional microphones. The microphones should be placed at least 1.5 m apart to reduce crosstalk.Missing: configuration | Show results with:configuration
  21. [21]
    DPA Microphones Deployed For A Range Of Events Around The U.S.
    Dec 21, 2022 · I barely used any EQ on them and, as expected, the main Decca Tree setup with DPA 4006 performed beautifully, striking the right balance ...
  22. [22]
    ELA M 251E - Telefunken Elektroakustik
    The ELA M 251E is a reissue of a legendary mic, with a smooth, open sound, ideal for vocals and acoustic instruments, and has a warm, clear tone.M 950E Tube Microphone... · M 850E Tube Microphone... · M 950ES Dual Tube...Missing: Decca emulation replicas
  23. [23]
    A Look At The Decca Tree Stereo Recording Technique
    The spaced pair is a great technique for stereo recording, and a variation used on orchestras for more than 50 years is the Decca Tree.Missing: first date commercial<|control11|><|separator|>
  24. [24]
    Kenneth Wilkinson - Positive Feedback
    Nov 13, 2020 · ... 1950s ... famous "Decca Tree." Kingsway Hall had been Decca's classical recording studio since it was originally leased by Decca in about 1926.
  25. [25]
    What are some classical recordings that were made using the Decca ...
    Sep 25, 2021 · Well pretty much the entire Decca catalog of symphonic works 1955 to the early 80's would be Decca tree in 3 or 5 mic configurations.
  26. [26]
    An Extraordinary Recording of the Beethoven Septet
    Jan 1, 2021 · The legendary 1959 Decca Tree microphone setup had worked its magic once again. And, as good as it was, we were surprised to discover that side ...<|separator|>
  27. [27]
    Kingsway Hall | The Skeptical Audiophile
    Wilkie's Decca Tree recording is overflowing with the kind of clear, spacious, realistic sound that can only be found on the better vintage vinyl LPs ...Missing: reverb | Show results with:reverb
  28. [28]
    Decca Tree Recording - Page 7 - Gearspace
    Nov 27, 2017 · ... Decca tree"... on chamber music I found some other preference. ... I am pretts sure, he refers to a scaled down version, without outriggers ...Several questions concerning Decca treeDecca Tree Spacing?More results from gearspace.com
  29. [29]
    Abbey Road Head of Audio Products, Mirek Stiles, writes about what ...
    Dec 4, 2018 · Most spatial arrays, beyond the Decca Tree, were alien to me before taking part in a joint experimental recording session with Gavin Kearney ...
  30. [30]
    Mics for orchestral film score recording? - Gearspace
    Jan 10, 2019 · It seems like the Neumann M50 is the standard for decca tree mics. I was wondering if there is a standard for outrigger mics for orchestral film ...Decca Tree Recording - Page 8Decca Tree w/ DPA 4060?More results from gearspace.com
  31. [31]
    The Evolution and Art of Immersive Audio Recording Techniques for ...
    Apr 29, 2024 · Techniques such as the "Decca Tree 3D", the "Polyhymnia Pentagon," and other arrays with omnidirectional microphones have a strong foothold for ...
  32. [32]
    Wondering if the Decca Tree is over-hyped a bit? - SOS FORUM
    Jan 13, 2024 · You need to add at least two outriggers (perhaps omni) and spot mics. It can end up a 100 channels if you do it the Deutsche Gramophone way.
  33. [33]
    Immersive Audio | SCHOEPS Microphones
    For recording music in 5.1.4, 7.1.2 or 7.1.4 using a stereophonic approach, main microphones with spheres such as the “Decca Tree-3D” are used successfully.
  34. [34]
  35. [35]
    Classical Recording: A Practical Guide In The Decca Tradition
    ### Summary of Decca Tree Positioning from "Classical Recording: A Practical Guide In The Decca Tradition"
  36. [36]