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Author Topic: Measuring for ORTF when using a Riser  (Read 3869 times)

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Offline KenH

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Measuring for ORTF when using a Riser
« on: February 11, 2009, 11:34:09 AM »
Sometimes my KM184's sound overly bassy and even a bit boomy. Running KM184s> V3 > digi > HDP2, almost always run ORTF 110deg, 17cm.

I'm wondering if there's a problem with my ORTF setup. When using a riser, how do you measure the 17cm ?

I know ORTF is 17cm, 110deg. Ideally (or necessarily) with the mics on the same horizontal plane (HP).  The KM184's can't be on the same HP because the ends meet, so ORTF is an approximation at best with 1 mic crossed over the top of the other. A riser is involved to achieve the desired height to get the top mic over the bottom mic to get the 110deg.

If looking at the mics from the top, they'd be at 110deg, and *if* they were on the same HP, they'd be 17cm apart.  Imagine using a clear hard flat plastic template with markings for ORTF - placed over over the mics and parallel to the floor (assuming a flat surface), you see if you're set up right. This is how I set my mics up.

But, since one mic is higher, the distance btw capsules must be >17cm if you measure the distance with a string or directly from center of the cap to the center of the other.  I'm wondering if this is a problem.

Do you measure 17cm from cap to cap or (Line B below) as if the mics are on the same horizontal plane (line A below) ?
   
In the picture below, B is greater than A.   

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Offline KenH

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Re: Measuring for ORTF when using a Riser
« Reply #1 on: February 11, 2009, 04:35:28 PM »
Noone has thought about this before ?    Or didn't I explain it right ?

With 1 mic crossed over the other, how do you measure 17cm for ORTF ?
Line B, or Line A, as if the mics were on the same horizontal plane ?
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Offline Todd R

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Re: Measuring for ORTF when using a Riser
« Reply #2 on: February 11, 2009, 04:45:31 PM »
I'd measure it as A.  The sound is coming at you from the horizontal plane, so theoretically there won't be a difference in sound anyway between the non-riser height or the riser height.  The important thing is to have the correct gap between mics in the horizontal plane.
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Offline JasonSobel

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Re: Measuring for ORTF when using a Riser
« Reply #3 on: February 11, 2009, 04:58:27 PM »
I agree with Todd, just measure the 17cm in the horizontal plane.  I will also add that it doesn't make much of a difference anyway.
If you assume that the vertical distance is 1 inch (2.54cm), set the horizontal distance between the caps to 17cm, and then use the Pythagorean theorem (A2 + B2 = C2), you'll find that the actual distance between caps is only 17.1887cm.  I truely doubt that you'd be able to hear a difference of 0.1887cm anyway, so don't worry about it.

(conversely, if the absolute distance between the caps is set to 17cm, and the vertical distance if the same 2.54cm (1 inch), again using Pythagoras, the horizontal distance between the caps works out to be 16.8092cm.  again, these are very small differences, and probably not worth worrying about.)

Offline Krispy D

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Re: Measuring for ORTF when using a Riser
« Reply #4 on: February 11, 2009, 07:46:46 PM »
Ken I dare you to hear the difference between your rig at 19 CM with one mic higher than the other, and 17 CM on the same hp.  I just don't think it matters enough for what we do.  I would bet the difference is inaudible.
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Offline KenH

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Re: Measuring for ORTF when using a Riser
« Reply #5 on: February 12, 2009, 09:50:54 AM »
Cool, thanks for the input, and thanks Pythagorus!   Eliminating that as an issue, then, I think I'm going to try using HPF on the V3 to roll the bass off, and see if that helps.
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Offline KenH

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Re: Measuring for ORTF when using a Riser
« Reply #6 on: February 12, 2009, 10:07:56 AM »
reducing your combined axis angle will really help as well.
Less than 110deg ?  How much narrower would be reasonable ?
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Offline Brian Skalinder

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Re: Measuring for ORTF when using a Riser
« Reply #7 on: February 12, 2009, 10:20:13 AM »
Relatively narrow spacing (17cm) + a relatively wide included angle (110º) will capture a fair amount of reverberant sound, which may contribute to the overly bassy or boomy sound you're experiencing.  As others have said, if you're otherwise happy with the overall recording, you might try increasing the spacing of the microphones while decreasing the included angle.  Narrowing the included angle may result in capturing less reverberant / more direct sound, while increasing the spacing should help maintain the overall stereo image.

Check out the sticky at the top of this forum that links to the Stereophonic Zoom and take some time to read and understand the SZ.  It's not the be-all, end-all, but should help you make some informed decisions about how to adjust your microphone configuration to address this and other challenges you may face in various recording environments.

For example, the SZ's Figure 9 indicates that the stereophonic recording angle (SRA) of ORTF (17cm, 110º) is approximately ±49º.  However, 35cm spacing with an included angle of 40º also produces an SRA of approximately ±49º.  So the stereo imaging of these two configurations should be very similar, but the greater spacing / smaller included angle should capture less reverberant / more direct sound.
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Offline KenH

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Re: Measuring for ORTF when using a Riser
« Reply #8 on: February 12, 2009, 12:34:18 PM »
Very interesting, I'll have to re-read the SZ.  Increase distance, decrease angle.

Thanks all!
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Offline ArchivalAudio

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Re: Measuring for ORTF when using a Riser
« Reply #9 on: February 12, 2009, 01:07:51 PM »
Ken
the  vertical off set is okay , which has already been addressed
I'm with you with running ORTF - that's mostly what I use
however
if you are not close enough yep = boomy
try
DINa (17cm @ 90°)
it still uses the 17cm (average distance between human ears)  which helps to create a natural tiem delay and the stereo image
and will also help to cut out some of that room boomyness

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Offline KenH

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Re: Measuring for ORTF when using a Riser
« Reply #10 on: February 12, 2009, 04:58:23 PM »
DINa (17cm @ 90°)
I've tried DINa and it is a bit better, but I wasn't all that pleased overall.   

I'm liking the increased distance, decreased angle approach.  Now I just need to get myself out to a show!
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Offline bluewingolive

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Re: Measuring for ORTF when using a Riser
« Reply #11 on: February 13, 2009, 10:19:45 AM »
I think you should ditch the KM's.   :P

Offline KenH

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Re: Measuring for ORTF when using a Riser
« Reply #12 on: February 13, 2009, 11:49:19 AM »
I think you should ditch the KM's.   :P
Always a wize guy in the house  >:D     I've been considering it, though...
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Offline JasonSobel

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Re: Measuring for ORTF when using a Riser
« Reply #13 on: February 13, 2009, 12:28:34 PM »
I think you should ditch the KM's.   :P
Always a wize guy in the house  >:D     I've been considering it, though...

if you want to tighten up that low end, a pair of Microtech Gefell m200 would do the trick  ;)

seriously though, I had a pair of km184's for years before I got the gefells - I'm familiar with both sets of mics...

Offline jrdead

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Re: Measuring for ORTF when using a Riser
« Reply #14 on: February 14, 2009, 02:14:21 PM »
I've also noticed that quite often when running ortf my recordings sound boomy, even when recording outdoors where i wouldn't expect so much reverberent sound. And at other times, ortf has produced some of my favorite recordings. It seems like distance from the sound source may be the culprit. If i can't be within the first 15 rows i don't think i'll be running ortf anymore. Does that seem reasonalbe?

 

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