The Modified Decca Tree Project

The mission : Record the chamber choir singing “O Magnum Mysterium” in the music lodge.

The strategy :

Quick links on Decca Tree :
The Decca Tree []
Decca Tree – origins and surround usage [PDF]

So, the original Decca Tree consists of 3 omni mics arranged in a triangle – to get both the worlds of spaced pair stereo field and coincident-pair accuracy. I’m not going to go on about the Decca Tree, if you’re interested to find out, the two links above should provide enough detail to munch on.

So there’s the original 3-omni decca tree – and then the slightly modified with 2 omnis at the back and an M-S pair in front to give more accuracy if needed. Now, the MS pair requires a figure-8 mic + a normal cardiod, but I only had two C414B mics available, and they are the only ones I had which were switchable between cardiod/h-cardiod/fig8/omni (newer ones have wide cardiod as well, but these old B-ULS didn’t have it). Other mics at my disposal – 2x AKGC3000B condensers (cardiod/h-cardiod), 4x AKGC1000S hyper/cardiod condensers, 2x AKG C451B cardiod condensers.

Obviously I only had 2 omnis available so if I were to do a decca tree the 2x 414s would have to go to the back, leaving only cardiods&h-cardiods left, not enough to do any sort of M-S / Blumein pair (2x fig8s). (It would be interesting to try out spaced cardiods, though)

Final decision – Decca Tree being a new step for me, I decided to play it safe, setting up my usual ORTF C451B pair in the centre front as a fallback, and also as the front mic mix in the decca tree. Not knowing how a timedelay+intensity front near-coincident pair would affect the mix when the two rear omnis were added, I also decided to add in the (only intensity-based) crossed-pair C3000B, which I reasoned would kind of ‘imitate’ a rough M-S setup (I haven’t tried MS though, so I can’t say).

MISSION INTERRUPTION : Chamber choir would NOT be recorded on the day of planned recording – due to certain ‘key’ singers being absent, so the recording would have to be postponed.

Oh well, I shall not have brought in all my equipment for nothing. I still decided to try out my new setup, very roughly. Now, as my understanding (and experience) goes, the decca tree is suited for large ensembles such as (choirs?) orchestras or large instrumental sections. However because of the cancellation, I decided to use it for an unusual use – to record a piano+saxophone.

Since it was just a test, I decided to set it up roughly. Standing in the middle of the base of the triangle, (my assistant) extended his arms forwards and placed the XY + ORTF pairs in front, then extended his hands either way and I placed the omnis at either side, forming a triangle.
Omnis were raised up to about 2.5metres (not sure, I can’t estimate) while the centre pairs were put at about 2.2metres. (Now, I think the verticle distance between them could be smaller, and I think I set it up a bit too high). My positioning in the hall wasn’t good – I set it up in the middle, too far away from the players, but I was too lazy to move it all after that (would have to move ALL the mic stands, since I don’t have a DeccaTree T-stand).


Decca Tree Demo [MP3 128kbps, 13sec, 204KB] – Alex Neville-Payne on Alto Sax, Me on piano, playing, well, Londonderry Air.

Please don’t overload my server by downloading it too much, haha.

Thoughts –

Gave a nice wide stereo field, excellent low-end response (give it to those 414s), horrible location for recording (too much room noise – I set it up too high and too far, I think), I think one of the C3000B mics was facing the wrong way, giving me some really weird effects. HF response was a bit low as well, not sure why.

I have not had the chance yet to listen to the recording on proper headphones/monitors, so my conclusions may be, well, inconclusive. Or inaccurate. It’s almost impossible to judge on headphones. But actually I think the array gave an accurate feel of what the room sounds like (horrible!) so I’m please. I’ll probably make some minor changes for the actual choir recording. And Mr. Rhind-Tutt may be able to get me a 3rd AKG C414 for the recording, in which case I can set up a proper M-S front pair! I’m quite happy with the recording, given I didn’t actually measure the distances between mics or anything – (even the height of the spaced pair wasn’t the same, as seen in the picture below)

So now when do I get to record the actual choir?

Some low-quality images taken from a camera phone :
Hard to see the centre pair, you can make out the 414s on either side

Laptop & Soundcraft mixer & E-MU 1616M

The centre pair up close! C3000Bs on top as crossedpair, C451Bs on the bottom as ORTF!

Some ORTF [17cm, 110 degrees apart] C451B samples for reference :

Harpsichord(me)&Recorder(Katy) [MP3, 188KB] – This was from the evening recital with me set up in the worst place possible, at the back of the room. Katy said I could use this 12second sample, at least I think she said I could hehe. One of my less successful sounding recordings, but given the circumstances, it was great!

Piano+Fr. Horn [MP3, 110KB] – Slightly better recording (Horn played by Edwin Li, piano by me) – although angle was too wide between the two mics, I discovered later.

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