Towards an easier ORTF setup

[Colin McDonald]

I was going to add this on to the Audio micing church choir thread but I think it merits a new one.

I find that getting an accurate ORTF set up can be a real pain even using the DIY ORTF protractor and a supply of paper measuring tapes retained after shopping at Ikea. It often seems nearly impossible to get both the angle and the distance correct because of the mic cables getting in the way.

I was recently asked to record a 40-50 strong choir's first performance of a work new to them for their edifiction and discussion at the next rehearsal. I knew it wasn't going to be a great recording as the choir sing to a CD backing track which was to be played as a mono mix from four different places round the choir. I explained to them it was going to be difficult to achieve any great degree of separation of performers and the (probably rather muddy sounding) backing track. However, I considered that a well placed ORTF stereo array would pick up the choir well enough to do the job with a clear stereo image and that proved to be the case.

After many years of cobbling up tall stands from bits and pieces, gaffer tape and sandbags I finally acquired a proper tall stand - a K&M 20811 boom stand. That proved a joy to work with - solid well built and very stable - but the mic array proved very fiddly to set up, especially as it was at the end of the horizontal(ish) boom arm. I spent ages the day before the gig trying to get the ORTF angles and spacing correct. In the end I used a combination of a Rode stereobar (the vertical spacers are most useful), the shockmounts from a Rycote Invision stereo kit because I was using a pair of Line Audio CM3 mics which can be very sensitive to handling/transmitted noise and a large Maplin gooseneck which I covered with black PVC tape to blend in with the rest (and to stop it looking like a bathroom showerhose). I was quite pleased with the result and it did the job and won't take anything like as long the next time. I've included a few photos below.

I would be interested to hear how other folks using ORTF arrays and who, like me, who not have the budget for the rather nifty DPA solution manage an overhead ORTF array, and how easy it is to set up.

There were also a couple of Rode NT55 cardioid spots for soloists and an omni (low pass EQ'd in post) to give the backing track bass a bit of oomph.

[John Murphy]

I use a C-stand with a grip arm. Made my own stereo bar. I use Rode NT1's and they come with very good shock mounts. The stand is chrome so I dress it with black gaffers tape. Looks fine from about 3 feet. It reaches around 10 or 11 feet. Couple of sand bags and its very sturdy. j

[John Nantz]

Colin - this is a very great starter post! I’ve been quietly working on trying to create an ORTF rig with my 414s and this is helpful. More on that in a minute.

With the intent on having various mic support options, last month, actually starting late December, I started searching eBay listings for “parts”, mainly a whole bunch of thread adapters like 1/4 > 3/8, 3/8 > 1/4, 1/4 > 5/16, 3/8 > 5/16, etc, and etc., a real assortment, and some are still in transit. Got an extra boom arm, adjustable stand mount/holder, and sand bag.

Back to the ORTF rig: I’ve found several support bars on eBay that could work but haven’t ordered one yet. The Røde one you’re using looks like a good choice. I had looked at it but hadn’t figured out how to get the mic spacing at a slightly different height but your post mentioned “(the vertical spacers are most useful)” so that is very helpful info. I had seen the pictures in the listings but there was no description about how they got the mics at a different vertical height.

For eBay searches, I’ve been looking under “Musical Instruments & Gear” > Pro Audio Equipment > Microphones and Wireless Systems [search term ORTF], Pro Audio Equipment > Stands, Mounts & Holders. A couple bars of interest were the K&M 23510 and the On-Stage Stands MY500.

Also looking at getting some more “sand bags” but there are so many styles and colors to choose from. Thinking of using water bottles instead of sand.

Going forward, for choir work the ORTF arrangement looks like the easiest approach, with establishment of the overlap angle being what seems like a difficult and critical part.

Really great post!

For the collectors and audio history buffs, came across an interesting eBay post:
“TUNER FM MONOPHONIQUE ESART ORTF FRENCH BROADCAST CONSOLE RACK PART”
A couple months ago I read about the history of how the French came up with this system and it was very interesting.

[Colin McDonald]

Thanks for the replies so far. I meant to add that for most choral performances - especially those which involve pipe organ - I go for spaced omnis, but on this occasion I needed a bit of focus while still being able to cover the whole width of the choir.

There’s an iPhone app called Stereo Mic Tools (screenshot attached) which predicts the angle of coverage for various stereo setups and lets you see what changing distance or angle does to the coverage.
Useful, but you still have to test the setup and listen carefully and adjust if it’s not sounding as hoped.

There’s also a Neumannn app dedicated to their mics for those lucky enough to have the budget for these.

Both apps are easier than looking up published tables for stereo imaging data, though the article linked is well worth reading.

EDIT: Answering my own question again, but just found this 3D printed CM3 ORTF mount. This appears to fit in a single shockmount.

The ORTF mic mount index page is at www.shapeways.com/marketplace?type=&q=ortf

[Steven Reid]

@Colin, I use a ShapeWays mount for a pair of Line Audio CM3s in wide ORTF configuration. There is nothing faster, easier, and more compact (visually unobtrusive) that I've found for mounting a stereo pair in my years of recording (see pic).

[Bruce Watson]

Originally Posted by Colin McDonald

I would be interested to hear how other folks using ORTF arrays and who, like me, who not have the budget for the rather nifty DPA solution manage an overhead ORTF array, and how easy it is to set up.

Most people wanting ORTF or NOS typically use a spacebar similar to your Rode. Grace Designs makes a nice one, etc.

Yours is the first I've seen using a gooseneck. Most people seem to use as little mic stand as possible, meaning they'll mount the spacebar on the top of the stand and raise it into position. No boom, no gooseneck. Nice and balanced so fewer sandbags. Those that use a boom tend to extended it at not much more than a 30 degree angle; few put a boom at a 90 degree angle like you are showing in your pix. The reason is that it's usually quite difficult to balance such a configuration.

If you're really interested in stereo configurations, you might want to search around the Gearslutz location recording forum. All kinds of acoustic location (that is, not studio) recordists people there, from amateurs like me to Grammy winning pros. And lots has been posted over the years on how to do ORTF, the pros and cons of various spacebars, stands, tall stands, etc. so search around and see what you can find.

[Colin McDonald]

Thanks for your post, Bruce.

Yours is the first I've seen using a gooseneck. Most people seem to use as little mic stand as possible, meaning they'll mount the spacebar on the top of the stand and raise it into position. No boom, no gooseneck.

You are of course correct about the normal mounting of an ORTF setup, which is on top of a vertical stand, but actually the reason for using the boom was the required placement of the mics closer to the choir (sorry I didn’t have time to do photos at the sound check or performance). Placing the mics on top of the main stand would not have separated the choir enough from the backing track as there were 2 of the stage monitors used for playing the backing track to the choir placed right at the base of the boom stand and I couldn’t persuade their tech to change their normal setup for the recorded performance.

The reason for using the gooseneck is the boom :-) - the array would otherwise have been at 90 degrees to the normal orientation of an ORTF setup.

I note with interest that the shapeways 3D printed mount I linked to above seems to require a similar (horizontal) attachment of the shock mount to whatever holds it - mounting in on top of the main stand would result in the mics pointing at the floor as far as I can see, but I’ll confirm that when mine arrives.

Nice and balanced so fewer sandbags.

As I mentioned in my first post, that K&M stand is extremely stable without any sandbags, but your point is taken.

Those that use a boom tend to extended it at not much more than a 30 degree angle; few put a boom at a 90 degree angle like you are showing in your pix.

Not to be pedantic, more in the interests of further explaining the setup I ended up with:

the boom was in fact at a downward angle to fit in with the natural resting angle of the gooseneck under the loading of that particular array.

Thanks for the GS tip - that’s where I found the shapeways mounts :-)

I’ve been a contributor there for a while (though not on this topic) - perhaps I should have looked there first before making my initial post, but I’m unrepentant about starting a discussion on dvinfo following on from the “Audio mixing church choir” thread.

Sorry if the above appears in any way ungrateful - your points are indeed most valid.

[Paul R Johnson]

I'm a bit amazed to be honest here. The biggest issue for me is always the location, and the makeup and physical placement of the sound sources. To many people, not enough people - too much or less depth available, and of course stage size compared with the available mic position.

If you couple this with the fact that if you change the angle of the mics, or adjust the spacing, the difference in anything other than a superb room, with amazing performers is so small it frequently cannot be heard. In many cases, the 'perfect' setup is compromised by the fact that when you stand at the microphones, very often the on axis direction is not where the sound source is!

Toeing the mics in because the width is less than you expected, or for some reason the performers are clusters with a gap centre - one I did last year had the piano dead centre for the second half of the evening, so the choir and musicians were all either side of it, with hardly anyone on centre line, because the full stick lid blocked their nightlines. In this case, I opened the angle out, which of course produced the hole in the middle - but the outermost violins were quite a angle from centre.

If you have never tried recording X/Y AND a spaced technique at the same time - just listen and see if you can tell the difference. You probably will hear one - but can you tell which is which?

The use of a protractor just made me smile.

[John Nantz]

So, for discussion purposes, if one has a couple cardioid pattern mics set at an angle, say, 110º give or take, is the overlap (too much or not enough) not that big of a deal? Or just not that big of a deal compared to all the other factors such as the mic’s placement relative to the sound sources?

My on-line “research” seemed to indicate that if there was too much of an overlap that the combined signals could be too strong; hence, something important and to be avoided.

Editorial comment: It’s getting more difficult to post a picture on line now because everything I looked at cautioned that “Images may be subject to copyright.”

Edit: If the angle isn't crucial that would make my life so much easier! I was actually thinking of how I could "map" the overlap using the vu meters on the Tascam while running a signal through the mics.

[Steven Reid]

Originally Posted by John Nantz

So, for discussion purposes, if one has a couple cardioid pattern mics set at an angle, say, 110º give or take, is the overlap (too much or not enough) not that big of a deal? Or just not that big of a deal compared to all the other factors such as the mic’s placement relative to the sound sources?

My on-line “research” seemed to indicate that if there was too much of an overlap that the combined signals could be too strong; hence, something important and to be avoided.

John, if you're willing to spend a little (more) time, you might like playing with this visualization tool for stereo recording to understand better how microphone polar patterns, distances, and angles affect what is recorded and, especially, what you hear in playback through two speakers. It might help shed light on what is "a big deal." Ultimately, your ears will be the best guide.

As an example, I regularly use a main pair of SDC's that are actually sub-cardioids. The tool to which I linked above will tell you that in ORTF configuration for these microphones, the stereo recording angle (SRA) is quite large (146.4*), meaning that when the microphone pair is placed beyond a certain distance from performers, the stereo image on playback will seem "squashed", e.g., musicians at far left and right will sound/appear closer together upon playback. In contrast, in an NOS configuration (or wide ORTF), the SRA is reduced to around 100*, meaning that the stereo image as recorded will be better spread between two speakers upon playback, e.g., far left musicians actually sound/appear far left. Hence, for my selection of sub-cardioids, *and all other variables being the same* (room, distance to performers, height of mics), I use NOS or a wide-ORTF configuration.

Is this a "big deal"? Probably not to a casual listener. But the attention to the details above will likely expose the most pleasing stereo image over one that is just OK.

[John Nantz]

That’s an interesting link. I played around with various settings, including the polar patterns and the ORTF configuration, and it appears that the combined polar is not affected all that much with angle, assuming the resultant polar is reasonably accurate.

Question: what about the distance from the source? Couldn’t find an input for that, or the width of the source. Or does one need to calculate this separately? Couldn’t figure out the meaning behind the various colored bars.

#2: Are there some instructions that go along with this? Note: I didn’t go to the link in the bottom right corner under “Program information”.

I hope Colin comes in with his questions!

[Gary Nattrass]

Another reason I personally use an MS mic ( Sony ecm-MS-957) it is far easier to place and is less likely to be in shot or disturbed. The Sony outputs A/B and has a rotating front capsule so you can have it end fire or side address.

[Steven Reid]

Originally Posted by John Nantz

That’s an interesting link. I played around with various settings, including the polar patterns and the ORTF configuration, and it appears that the combined polar is not affected all that much with angle, assuming the resultant polar is reasonably accurate.

Question: what about the distance from the source? Couldn’t find an input for that, or the width of the source. Or does one need to calculate this separately? Couldn’t figure out the meaning behind the various colored bars.

#2: Are there some instructions that go along with this? Note: I didn’t go to the link in the bottom right corner under “Program information”.

I hope Colin comes in with his questions!

I'm not sure what you mean by "combined polar" and "resultant polar." The tool simply allows you to visualize a stereo recording angle (SRA) when you fix certain variables. Distance to a sound source is not a variable because that doesn't affect SRA. Rather, as the link to "program information" explains, you can gauge (or even input for reference (two of the colored hash marks)) an orchestra recording angle, which is obviously fixed once you pick a distance from sound source to microphone. Then select polar pattern, angle, and distance between microphones to adjust SRA accordingly. If you're forced to mount microphones, say, unusually close to a wide-spread orchestra (because of venue physical constraints), then you probably would adjust variables to result in an SRA that is wide enough to cover most of the orchestra without, hopefully, leaving a 'hole' in the middle of your stereo image. Too narrow an SRA in this example would result in a lot of musicians being hard-panned left and right. Yech.

I hesitated introducing a link to this handy tool in the thread because it addresses just one factor among several others, such as placing mics to balance direct and diffuse sound, height of microphones, angle with respect to floor.

In reality, at a live performance where sight lines, conductor preferences/ego, physical constraints of the venue, and precious time to set up often work against the fiddling of mic placement, I can just set up a pair of SDCs in ORTF or NOS configuration and be confident that the configuration's relatively forgiving nature and my placement got me to ~90% of where I needed to be. And making *that* happen in a timely and easy manner hopefully brings my little diversion back to the OP's post and my reply showing one way that I mount a pair of mics.

[John Nantz]

Originally Posted by Steven Reid

I'm not sure what you mean by "combined polar" and "resultant polar."

Understand ... I should have explained it but ... mea culpa. My thought was the additive or cumulative effect of the left (L) plus the right (R) mic polars. Where the two (L & R) polars overlap there should be more volume but the grey polar curve, for some reason, didn't have a bump to show that. So that seemed odd.

Originally Posted by Steven Reid

The tool simply allows you to visualize a stereo recording angle (SRA) when you fix certain variables. Distance to a sound source is not a variable because that doesn't affect SRA. Rather, as the link to "program information" explains, ....

That first part is what puzzles me and I'll have to follow up and read the "program information". But my thought was that the fore and aft distance to the sound source, a choir in our case, would be a factor to consider because one wants to capture the whole width of the group in a good part of the cardioid but, I think, not necessarily a whole much beyond that otherwise there could be extraneous (non choir) noises being picked up, such as audience coughs or maybe even room acoustics. Of course, when the choir is singing then everything should be quiet so maybe that's not a problem.

In my case, last December, the harp was way off to the far left side of the conductor and forward of him by maybe 2 or 3 feet. In the ORTF mode with minimum L & R overlap the left mic would have easily captured it so that should be good. In other cases, there is usually a piano sitting in that approximate position.

Originally Posted by Steven Reid

I hesitated introducing a link to this handy tool in the thread because it addresses just one factor among several others, such as placing mics to balance direct and indirect reflections, height of microphones, angle with respect to floor.

Thanks for the link and pointing out the limitations.

Originally Posted by Steven Reid

In reality, at a live performance where sight lines, conductor preferences/ego, physical constraints of the venue, and precious time to set up often work against the fiddling of mic placement, I can just set up a pair of SDCs in ORTF or NOS configuration and be confident that the configuration's relatively forgiving nature and my placement got me to ~90% of where I needed to be. And making *that* happen in a timely and easy manner hopefully brings my little diversion back to the OP's post and my reply showing one way that I mount a pair of mics.

Great wrap-up! Very appreciated.

Gary - I'll check out that Sony ecm-MS-957 mic
Sooo much to think about!

[Steven Reid]

Apologies for further hijacking...but, John, I think you're addressing all good points and questions. Might I suggest you enjoy some time reading, searching, and listening within the audio sub-forum that Bruce linked above? In addition, I can recommend an excellent book on recording that, I think, more than adequately addresses your points in very accessible prose. (FYI, I've read and learned from it!)