String quartet - 3 condensers, some 57s\58s

[Hugh Robjohns]

Not much... Try it!

[Aural Reject]

Good that it went well but what's ortf ____ at 90*?

You and me both, eh?

For the benefit of others, the French ORTF mic array has a very precise specification: 170mm capsule spacing with a 110 degree mutual angle.

If the stereo mic array doesn't have that exact spacing and that exact mutual angle, it ain't ORTF... it's simply a near-spaced stereo pair of your own design.

For reference, there are several other precisely defined near-spaced mic arrays, such as the Dutch NOS (300mm and 90 degrees), or the German DIN (200mm, 90 degrees)... etc

Varying the capsule spacing and mutual angle alters the stereo acceptance angle and the imaging, and altering these parameters along with the distance from the source helps to find the optimum sound stage and aural perspective. So there's nothing wrong with altering the mutual angle or capsule spacing of an array to achieve the desired sound... just don't call it a defined array when it isn't because it causes unnecessary confusion (and sometimes mirth )!

I’ve used the ORTF system and even got the measuring tape out! and it’s worked fine, but I’m wondering, how much does it have to be out so you’d hear a difference?

As Hugh has said, using your ears and fiddling on appropriate lab monkeys is the best way....but if you cba or don't have a home office licence....

http://www.sengpielaudio.com/HejiaE.htm

[Hugh Robjohns]

The sengpiel calculators are very good, but I mostly use the Neumann Recording Tool app on my phone to visualise mic arrays tweaks as it's interactive and quicker to use (and easier to do when on location).

As a general rule, though, reducing either the mutual angle or the capsule spacing of a stereo array reduces the source width as heard over stereo speakers (and vice versa).

This is because reducing the mutual angle (or spacing) means the interchannel level (or timing) difference for an off-axis source also reduces. Smaller level /timing differences between channels produce images closer to the centre — hence a narrower source image.

Thinking of it on a different way, if you reduce the mic angle/spacing then to appear fully in one or other speaker the off-axis source has to go even more off-axis.

As a guiding technique to optimal mic array placement, I'd suggest rigging what you think might work — ORTF or whatever — switch the monitoring to mono, and move the array nearer or further from the source until the perspective (direct/reverb balance,) is just on the dry side of ideal.

Then revert to the monitoring to stereo and notice the slightly more reverberant character. Repeat adjustments until happy with the mono/stereo compromise.

Next, consider the stereo imaging. Does the source fill the soundstage appropriately?

If it's too narrow, try increasing the mutual angle and/or capsule spacing slightly (5 degree and 1cm increments) — being mindful that more direct signal is potentially being captured off-axis and with more risk of comb-filtering, so generally with more colouration. Check mono compatibility again.

If the source is overly wide then consider reducing the mutual angle and/or capsule spacing.

Also, be aware that changes to the mutual angle and capsule spacing not only alter the stereo recording angle (and thus source image width), but also the image linearity or 'spatial distortion' — the relationship between the incidence angle in the recording environment and the perceived angle in the stereo image portrayed by the speakers.

Spatial distortion can be significant in some configurations, which is why we have different standard arrays optimised for different stereo recording angles.

For more on that, see Michael Williams' books and articles.

[Aural Reject]

The sengpiel calculators are very good, but I mostly use the Neumann Recording Tool app on my phone to visualise mic arrays tweaks as it's interactive and quicker to use (and easier to do when on location).

Totally agree…but I’m, er, cough on a coffee break in the office and had that bookmarked

[Drew Stephenson]

As a general rule, though, reducing either the mutual angle or the capsule spacing of a stereo array reduces the source width as heard over stereo speakers (and vice versa).

I do find this weirdly counter-intuitive. My primitive brain says that if you narrow the mutual angle, the actual source takes up more of the space between the on-axis lines of the microphones, therefore when you play it back it should come out as a wider sounding source. A bit like zooming in with a camera lens.
I understand why this isn't the case, from your answer below, but my brain is really not happy about it!

[Hugh Robjohns]

I do find this weirdly counter-intuitive.

You're not alone. Most students of the subject struggle too.

My primitive brain says that if you narrow the mutual angle, the actual source takes up more of the space between the on-axis lines of the microphones, therefore when you play it back it should come out as a wider sounding source.

What matters to the speaker image is the interchannel level difference. More width needs more difference... but a narrower mutual angle gives less difference — and when the angle is zero, no difference and thus dual mono.

[Wonks]

I often find things are often easier to understand if you take them to one extreme or another. in this case, assume that both mics are parallel to each other and close together. It's easy to see that the stereo image width would be small/almost non-existent and you'd get close to a mono image.

Moving the mics apart, or widening the angle between them (within reason), can then only give you a wider stereo image.

[Drew Stephenson]

(still don't like it though!)

[Arpangel]

(still don't like it though!)

I’ve tried a textbook ORTF pair on our piano and it didn’t cut it, I’m using a wide, spaced pair of cardioids about 18 inches off, and it sounds like our piano, perfect.

[tea for two]

Zoom H2n has M/S facility which I wasn't aware of until now.

Reviewed 2012
https://www.soundonsound.com/reviews/zoom-h2n
"Initially I wondered if the M/S facility would work properly or be a marketing gimmick, given that this is a budget product. I'm happy to report that I found it extremely effective. Although the parameters can be adjusted on-board, in RAW mode, I found leaving this until the mixing stage was the best option, and the M/S decoder was joyously simple to use.

The quality of the mics is about the same as those on similarly-priced products I've tested: sound quality is reasonably good, and certainly usable, but not exceptional. Importantly, handling noise is very low — all the more impressive when the entire recorder is about the price of a typical budget condenser mic!"

So now I'm interested in acquiring H2n 2nd hand so as to checking out its M/S facility.