I would like to learn more about using the (Optimized Cardioid Triangle) technique

[Doozer]

Do any of you seasoned veterans have any experience using the (Optimized Cardioid Triangle)? I have been using Schoeps MK41s in the ORTF configuration for orchestral and choir recordings for a few years. I augment the 41s by flanking left and right a pair of MK21s. I use the 41s for my main pair because I am usually in a less than desirable acoustic environment and the near omni would not eliminate enough of the unwanted reflections. I am considering purchasing a third 41 for a center channel and using an omni and low pass filter to fill in the low range. I would like to start a discussion on this technique with some of you folks who have some field experience using the Optimized Cardioid Triangle.

[Doozer]

If any of you have ever used this technique, would you post and let me know how you liked the results.
Thanks, Rick

[Zokuhei]

Hello Rick,

The OCT, as invented by Dr Günter Theile, is a set up with two supercardioids at the sides (mostly MK41, base distance 70 cm) and one cardioid (MK4) as center 8 cm nearer to the source. This system can be completed with additional 100 Hz lo-passed omnis (MK2s) at the sides for the low end.
I would also use a cardioid a the center, as the signals would be too devided to provide an open stereo picture. A half left signal would neither be picked up by one of the side SCs nor by the middle one.
I don't think the use of TWO omnis is absolutely necessary, as the wavelength at 100 Hz and lower is pretty much longer than 70 cm and so the stereo effect will not be as wide. But it could narrow the imaging, so that the whole picture will be disturbed.


We recently had some listenig tests at Detmold comparing 2 channel stereo to stereo + C recordings, which have shown, that the center channel provided an improvement in locating sources.
All recordings were made with Schoeps through stagetec Nexus pres and AD at 28 bit. Listening room was our Geithain room at ETI Detmold (sweet spot).
As you will need SACD and a good 3 channel monitoring system to hear the center and so the improvements, it will not be as mass compatible, but you can't deny them.


Tim Tautorat

[David Rick]

I've been using OCT arrays (and also various Williams LCR arrays) at a summer festival for three years now.

I find that the OCT gives me better control of off-side crosstalk, which results in better image stability compared to all-cardioid arrays.

With OCT, you can't design a "critically linked" 5-mic array as you can with the Williams tables, but I don't find that to be particularly necessary in a concert hall situation. Perhaps for a radio play.

I have the recommended Schoeps setup, with a pair of MK-41V's and a MK-4. But I've also had lovely results using a pair of Josephson hypercardioids (sadly, out of production) and a DPA cardioid in the center.

I do like to add the additional omni's when I can, but I space them wider than the hypercardioid mics -- as wide as my mounting bar will allow. Typically, I'll put DPA 4003's or 4006's facing upward, with the black grids on.

If you need to think about downmixing to stereo, you might consider an OCT2 array instead. This moves the center mic farther forward (compensated by electronic delay). I believe this is intended to make L&R less correlated after downmixing.

I'm not certain I totally agree with Tim on the improvement in imaging. One can get amazing imaging out of a carefully deployed hypercardioid pair. It's not as stable as OCT when the listener moves out of the sweet spot, but sitting "in the chair" I find the two-mic case to be less fatiguing to listen to. Maybe that's because of residual off-side crosstalk yielding confusing localization cues. Or maybe it's just that stereophonic listening is an acquired skill and we're all much more practiced at "decoding" L/R than LCR.

David L. Rick
Seventh String Recording

[Zokuhei]

I guess the wider spacing of the omnis is in fact the best use of them. To get real stereo imaging to the low bass might just have been left behind by Theile because just having one 70 cm bar seems much more practical.
How long is the stereo bar you're using? So how far do you tend to space the omnis, David?

The improvement in imaging was something I did not expect either. What I was totally sure about, was the fact, that LCR is the only way for stable imaging when you can not assure the sweet spot listening position.
The surprise was, that the statistics seem to show, that over 50 % of the tested Tonmeister (including me) have chosen LCR for most natural and best imaging in the blind test , sitting IN the sweet spot.
The LCR systems were not only OCT but also INA-front for example, after Hermann and Henkels, so the test does not totally fit in this topic, but for me, as someone who was also convinced, you're pretty used to 2 Channel stereo imaging it was pretty surprising.

Tim Tautorat

[David Rick]

Originally Posted by Tim Tautorat

I guess the wider spacing of the omnis is in fact the best use of them. To get real stereo imaging to the low bass might just have been left behind by Theile because just having one 70 cm bar seems much more practical.
How long is the stereo bar you're using? So how far do you tend to space the omnis, David?

If I recall correctly, I have a 1.3M bar. I was going to post a picture, but it's 60k too big to upload. I'll have to take the file home to resize it. (How does Steve post those giant photos? I guess he's a moderator.)

The improvement in imaging was something I did not expect either. What I was totally sure about, was the fact, that LCR is the only way for stable imaging when you can not assure the sweet spot listening position.

I agree on imaging, but many mix engineers still avoid using the center channel because the C speaker is inferior in many home theater systems. I don't avoid it; I figure I should make the best source material I can, and then it's the listener's responsibility to have a good system. If I produced pop music, maybe I'd have a different opinion.

The surprise was, that the statistics seem to show, that over 50 % of the tested Tonmeister (including me) have chosen LCR for most natural and best imaging in the blind test , sitting IN the sweet spot.
The LCR systems were not only OCT but also INA-front for example, after Hermann and Henkels, so the test does not totally fit in this topic, but for me, as someone who was also convinced, you're pretty used to 2 Channel stereo imaging it was pretty surprising.

The Tonmeister statistics are interesting. But I think in those tests were done with the LCR arrays designed and placed by the most experienced engineers, often the inventors of the technique in question. I'm very skilled at stereo array design and placement, but maybe my LCR array utilization is not yet as good!

Best regards,

David L. Rick
Seventh String Recording

[David Rick]

-- David

[audiothings]

please humor the 'n00b' with some pointers to resources on the 'OCT' and 'William LCR' arrays... have not come across them at the infamous 'microphone university', or other usual internet suspects...

if i may ask a more generic question, are these constructed as per some theoretical ideal or pure real world experience?

respect,

[David Rick]

Originally Posted by audiothings

please humor the 'n00b' with some pointers to resources on the 'OCT' and 'William LCR' arrays... have not come across them at the infamous 'microphone university', or other usual internet suspects...

if i may ask a more generic question, are these constructed as per some theoretical ideal or pure real world experience?

The most comprehensive discussion of OCT arrays and their alternatives is here:

Multichannel Natural Music Recording Based on Psychoacoustic Principles

"Williams arrays" are those tabulated by Michael Williams in a series of AES convention preprints. Preprints can be searched and ordered from the AES website . These papers have extensive design tables that allow you to choose an appropriate surround array for almost any recording situation. But if you use a laptop on location, Williams has put the whole set into a hyperlink document, which is available here: Michael Williams' web site.

Here's another nice web tool that helps analyze LCR arrays:

Image Assistant

To answer your second question: There's quite a lot theory behind these designs. Some of the theory is built atop a rather modest psychoacoustic foundation, IMO. But of course theory is just the starting point. Then comes listening, aesthetic judgement and adjustment. (Repeat until satisfied!)

David L. Rick
Seventh String Recording

[audiothings]

thank you sir!

looks like i have an interesting evening of reading ahead :)

[Doozer]

David, who is the manufacture of the surround microphone bar that is in the picture and where did you get it? I also want to thank all who participated in this topic; I check the post daily for input and I am reading the links.
Thanks, Rick Carlins

[RobAnderson]

Doesn't Schoeps make an OCT bar?

I recall it being a bit pricey...

[David Rick]

Originally Posted by Doozer

David, who is the manufacture of the surround microphone bar that is in the picture and where did you get it? I also want to thank all who participated in this topic; I check the post daily for input and I am reading the links.
Thanks, Rick Carlins

I built it out of AEA parts, Rick. I don't think they have a pre-configured surround package, but if you start with one of their Decca tree kits and add a few extra pieces, you can easily build what you need. Ever play with an erector set as a kid? Same idea, just lots more money!

http://www.wesdooley.com

-- David