The Decca Tree

September 14, 2022
 by Paul McGowan

Wikipedia describes the Decca Tree as a 3 microphone spaced array most commonly used for orchestral recording. 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 Ernest Wilkinson and his team at Decca Records, to provide a strong stereo image.

The classic Decca Tree setup uses three omnidirectional microphones arranged in a “T” pattern outlining a triangle, often equilateral; the center microphone is mixed with the two spaced microphones to fill the “hole in the middle” in their imaging; it points the sound source.

Here’s a picture of it.

This works really well for large groups or big halls, but it has a fatal flaw. Listening back to recordings I’ve made using this technique, the stereo image is really good but lacks the hall ambiance.  The perfect setup would have both hall ambiance and live stereo capture with control over the center fill.

As I get more involved in the recording process I wind up experimenting a lot. As mentioned in my post, Being There, the first step in any quality recording is to listen. Listen from every angle you can. Once you get a handle on how it sounds live you can then work to capture the essence and life you hear in the music.

(This is in essence the same technique we use designing equipment. Knowing what it should sound like we work with the circuits until it does. Voicing.)

One of the first lessons is that a single mono microphone doesn’t cut it. A singer, solo guitar or horn, or even a small group cannot be captured as they sound live with a mono microphone. Why? For the same reason you can’t either. Plug one ear with your finger and close your eyes and listen. We have two ears and two eyes for a reason.

What’s needed is a stereo microphone—even for a single source.

The most realistic stereo microphone setup I have found is the Blumlein. This two microphone setup was invented by stereo sound’s inventor, Allen Blumlein. The technique places two figure-8 pattern microphones at 45˚ angles to each other. This creates a 360˚ capture that looks like this:

Placed properly it sounds remarkably live. Many Octave recordings employ this method.

The modified Decca Tree setup I have been using as of late combines a Blumlein left and right capture with a center fill provided by the third microphone, typically a front facing cardioid pattern.

The results have been amazing and I cannot wait for you to hear them in upcoming Octave releases.

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31 comments on “The Decca Tree”

  1. Our ears being sound detectors are much more complex devices than a simple microphone. The shape of out head and our pinnae and ear canals act as filters detecting the vector characteristics of the sound waves reaching the ear resulting in the HRTF. Not to mention the complex signal processing of our brain! Thus a better mic tech I would be a dummy head. However there still is the problem of two loudspeakers creating inter speaker crosstalk.

  2. Wow…so that’s five microphones all up? 😮
    Fun, fun, fun!

    I wonder how the Cowboy Junkies managed to do it in
    1987 with only one single Calrec ambisonic microphone.

    1. The ambisonic microphone isn’t really just one mic but four closely spaced subcardioid or cardioid microphones arranged in a tetrahedron.
      Sounds like I know what I’m talking about?
      No, just repeating what I’ve read.

      Begs the question though, why doesn’t Paul use ambisonic microphones?
      Make everything four times better.
      Or just more complicated?

    2. Sam Phillips, maestro of Sun Studio in Memphis, Tennessee, used a single omnidirectional microphone to record early blues, country, rock ‘n’ roll, rockabilly, etc. The set up consisted of placing the mic on a stand in the center of the room and then using his ears to determine what he considered to be the optimal locations for the musicians to stand and sing and play to make a good recording. Masking tape ‘X’ marks the spots. Live in the studio. Fix it in the mix, wtf is that? Was it great fidelity? Well, not really. Was it great music at the dawn of an era? Absolutely!

  3. Awesome teaching and learning. I have learned more from this Forum that all Audio Forums combined since I began Surfing the Net regularly from 1996. Now I want to experiment with this on my SUNN MX4112 Mixer. Another project for my Man Cave.

  4. How about with a 5.n array? Use the Decca tree for the 3 front channels and plus a couple of spaced omnis further back to capture the hall sound to be mixed/balanced into the rear channels.

    And so to bed.

  5. Is it possible to include what microphone techniques used in the notes about the recordings. I believe you’ve upgraded the recording equipment as well. For instance I know you’ve been recording your newest Octave releases in DSD 256.

    Many buyers might want to know before purchase the technical parameters used during the recording.

    I’m sure all the Octave recordings issued are excellent.

    But it would be interesting to purchase several recordings since Octave was founded from the beginning to present to hear the progression in the recording chain and microphone layouts used. Perhaps the consumer could even provide feedback on the progression. I’m sure many PS Audio fans have systems that would discern the progression.

    Is there a beta testing program available?

    I’m interested because for maybe the first time the consumer could provide valuable feedback to the recording engineers. All in the effort to make the very best recordings possible.

  6. Unlike most audiophiles, I believe that playback is only half the fun. A *REAL* audiophile wants to go out, capture it live and bring it home. You’ve then heard it live and then have the ultimate reference to go against. Does it sound in your listening system anything like what you heard live? When you just playback commercially recorded music, you’re listening to the engineer at the other end as much as the music.

    So many audiophiles love the Miles Davis “Kind of Blue” recording, which I feel is one of the worst engineered stereo jazz recordings I’ve ever heard. Just awful. Bassist Paul Chambers sounds like he’s down the hall. You may want to chalk it up to it being done in 1959, but this recording of the Victor Feldman trio (Feldman on vibes, Scott LaFaro on bass, Stan Levy on drums) is terrific and sounds like it was done last week.

    In a world where people drop $4000 on a power conditioner or $6000 on a DAC, you can do remarkably good recordings with very modest equipment. Most of the recordings I’ve done over the past 20 years have been of my wife’s string quartet. All highly accomplished professional players from SF Bay Area orchestras. At the link below you can hear them, along with a local professional pianist, doing the Dvorak Piano Quintet. I have an image of the the performance which shows where they were sitting and the location of my microphones.

    I’m using a pair of modified Oktava cardiod condensor mikes ($600 used), in an ORTF configuration, run into a Focusrite Clarett 4Pre USB audio interface ($699 new today), into a Windows laptop ($250) running the free, open source Audacity software ($0). I’m recording at 96khz/24 bit resolution. The playback you hear here is done without EQ, reverb sweetening or down sampling. I just edited out the stuff before and after each track. My own favorite track is the 2nd movement. Here you are listening to the live, master recording.

    One of the issues with live recordings done this way, is that you only get what the musicians create. You can’t change the balance between them, and you have to live with the acoustics of the room. Every room sounds different. Paul talks about “hall ambience”. The way you try to capture that is to balance the sound of the room with the sound of the source – the musicians. You get more room sound the farther back you get, but you lose the presence and some of the imaging the farther back you go as well.

    The ORTF configuration is the French national standard, and has the mike capsules space 17 cm apart, angled at 110 degrees. You get two different cues from playback this way. Sounds are louder in one mike than the other depending on where the source is. The violinist on the left will be louder in the left mike than the right, thus playing back louder on your left loudspeaker. The second cue is that the violinist’s sound also reaches the left microphone first, and thus on playback, the phase of her sound will also be earlier in the left loudspeaker. I find this technique to give pretty good imaging. I assume that y’all have pretty good playback systems and in listening to these master recordings, will hear some decent imaging.

    I don’t have the luxury of using my own studio, controlled acoustics and a vastly larger budget like Paul does. I have a friend (with a much larger budget than mine) who does both Decca tree and Blumelein techniques. For his Blumlein work, he uses a 4 channel, one point cardiod mike, where all of the mike elements are oriented at 90 degrees from each other. He runs it into a four channel recording DAW (Digital Audio Workstation) on his Mac laptop. Depending on how he mixes it, he can do one point, coincident stereo recording, or Blumlein.

    A lot of guys like the Blumlein technique, but just like my ORTF method, is very dependent upon where you sit in the room. Most people who do this use a coincident pair of ribbon mikes. My friend with the 4 channel cardiod condensor mike can perfectly emulate a pair of ribbon mikes, but with a much greater accuracy as ribbons tend to not have anything like a flat response. He can also custom adjust the comparative gain on the front and back channels to give the kind room ambiance that sounds good to him. He mixes on his hi-end system at home, which is a pair of the Dutch & Dutch 8c studio monitors. Pretty sweet reference if you ask me.

    Before I got my current rig of the Oktava mikes and Focusrite Clarett USB audio interface, I used the VERY cheapest setup money could buy. I had a pair of Behringer C2 cardiod condensor mikes ($60/pair when last sold) and a used M-Audio USB audio interface ($100 used). Those recordings sound pretty damn good and far, far better than you’d expect. If you didn’t know how cheap the gear was, you’d still think they were wonderful recordings. Here is a master track using this embarrassingly low cost gear of my wife’s group doing the first movement of the Ravel String Quartet, using this gear, at 96 khz/24 bit. I think it sounds pretty decent.

    Spend all you want on your hi-end rig, meticulously clean your vinyl, and you still won’t have 1/10th the joy of bringing it home live from your own efforts.

    1. Russ, Thanks for the education on doing your own recording. I thought you comment about “Kind of Blue” points out something very important about. The most important thing about great music is the music. As audiophiles we all want our music to be well engineered when recorded, mixed and mastered and then played back on gear that does not alter the sound. However, good engineering and good sounding playback gear does not make great music. The only thing that makes great music is great music, like “Kind of Blue”. While poor engineering and poor playback gear can do a lot to harm great music, the best great music will come through even when poorly engineered and played back on mediocre gear.

    2. Agreed. I’ve been recording orchestras since I was a kid, recording the orchestrates my older sister played in, using my JVC cassette deck and a couple of radio shack condenser mics (back when cassette decks had built in mic preamps!). Good fun, and a great learning experience.

      I do love ORTF. Several years ago we used it, along with a wide mic pair and some spot mics, to record the American Bach Soloists performing Handel’s Messiah at the Grace Cathedral in San Francisico and it turned out excellent!

      1. Really? Betcha my wife was in the orchestra. She has both a “modern” violin, made by George Chanot in France, in 1848, and a “baroque” violin, made in France by Jacque Chappuy in 1774. She does both “modern” orchestral work and “early music” work and has played that show with ABS a number of times.

        1. It was around 7 or 8 years ago. There was a video crew there as well for two of the 3 nights. It’s on Blu Ray if you’d like to check it out. Those vintage string instruments are really cool, as is the harpsichord and foot pump organ.

    3. Excellent! Thanks for sharing Russ! Listening to this put me in a good mood while working on stupid computer spreadsheet. The major scale is a upbeat scale…
      For the sake of sneaking in some music theory – the A major scale (Dvorak Piano Quintet in A Major, Op. 81), relative minor is F# minor.
      Very same notes just rearranged at different starting points but has a darker more somber sound to it. Blues are played in the minor scale.
      To those who may be interested here is a link to the circle of fifths invented by Pythagoras.
      A Major has 3 sharps. Related minor is F#. You can change keys from A major (modulate) to D,b,c#, and E in the same piece of music to shift moods or tempos.
      The circle of fifths is a great tool to assist musicians compose music.
      Here is a link to Nocturne in F sharp minor for comparison to the sparkly A Major scale.

      Sorry for getting fire up and once again going off on a tangent.
      Thanks again Russ for sharing.

    4. Hello again Russ.

      You have some great live recordings there ! We have talked here before and I appreciate you efforts in using a very simple recording rig. I still don’t understand why Paul won’t try a straight pair of spaced omni microphones for recording the solo organ.

      You get TONS of room acoustic and the organ fills the right and left channels with glorious TWO CHANNEL stereo, none of that ‘mixed’ up stuff.

      Paul also never mentions the technique of a ‘coincidence pair’ or FULL coincidence pair, nor the ORTF which you and I have used and are equally common schemes.

      My latest recordings are single point Mid Side, does some nice things (is mono compatible) and also captures lots of space especially with organ/orchestra and chorus works (O:

  7. Would it better capture hall ambiance if instead of one single point source cardioid mic in the center, you used TWO in an ORTF or near-ORTF arrangement? Love learning about all these techniques. Thanks!

    Oh, just want to mention that it might be slightly confusing to newbies, that the picture of the Decca Tree above does NOT have that third mic screwed in place in the center but you can see where it would go, however I thought if you were “really” recording you’d want it about 1.5 meters in front of the others, and that photo looks like it hasn’t been finished setting up.

    1. Yup, there could have been a better example photo for us. You can buy nice Decca Tree mounts these days that are not too expensive. Mixing the 3 omni mics is an art. A pair of omni mics will not ‘localize’ the musicians on stage, but adding the center makes that all happen when mixed correctly.

  8. Paul, Do have a link to a reference for the Blumlein diagram that you posted. I would be nice to understand what it means in more detail. For example what do the small light green arcs between R and R2, L and L2, … represent?

  9. Another interesting variation of the Decca tree is to use an MS mic for the center instead of an omni. That gives you the flexibility, post recording, to focus the center by being able to adjust the center’s width from omni all the way to cardiod.

  10. These recording techniques were invented and developed in London, primarily for classical recordings and live broadcasts. The sound quality was perfected because the sane venues were used by the same engineers with the same performers over decades. The same applies to many artists/labels around the rest of the UK and Europe. Very few recordings that I listen to are made in studios. I have very rarely had issues with the quality of classical recordings.

  11. My Hauptwerk organ program utilizes six channels of long samples recorded simultaneously from L and R at the organ console, L and R midway out in the nave or hall, and L and R near the back of the nave or hall. The adjustable mixer allows the channels to be mixed real time to suit the player’s preference. I think the best sound is a mix of the console (closeup) samples and the midway out in the nave or hall samples. If I want even more ambience I can add in the near back of nave or hall. If I use only the close-in samples the pipes sound drier with more emphasis on the high frequencies. Adding in the remote samples results in a fuller sound with more emphasis on the midrange and lower frequencies and reverberation. High frequencies attenuate faster than low frequencies when travelling through space, and this is noticeable in large churches and cathedrals. It is nice to be able to adjust the virtual listening position on the fly and not rely on a fixed position chosen by a mixing engineer.

    Another great feature of Hauptwerk is that every voicing parameter of each individual pipe (tone, amplitude (volume), frequenc emphasis, chiff, etc.) can be adjusted to suit the room and listener’s preference. It is like voicing a real pipe organ when it comes from the factory and is assembled in the space. Any objectionable room anomalies can be tamed through this voicing procedure to produce a well-balanced sound customized for the space.

  12. Just a quick comment to applaud Russ Button for offering his perspective on this post.

    If you want to explore just how good Blumlein technique can be, listen to what Kavi Alexander has accomplished. His many excellent releases on his own Water Lily Acoustics label showcase the benefits of that technique. It works particularly well more for intimate close-up recording opportunities, rather than for use in very large halls. All dependent upon placemevt and the hall, of course.

    Another interesting technique which has proven useful to me when capturing orchestral performances, is to place an ORTF pair centrally, over the conductor’s position and also place flanking omnis some distance, to the left and right, with respect to the central ORTF pair. Careful level adjustments can render a good sense of space and localization, again, all depending upon the hall.

    I prefer to use Milab DC-196 microphones for a great deal of my live archival recordings. The flanking omnis are usually MBHO 603’s

    Happy listening!

    1. Over the music director is usually the problem with commercial recordings of orchestral performances. Strings always sound up front and too close and don’t often sound like they are in the same space as the rest of the ensemble. Case and point, if there isn’t artificial reverb added in post, they are drier then the brass section at the rear of the stage.

      I want to pull the bows out of my ears and NOSE LOL.

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