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Intensity Difference and Time Difference stereophony in about equal proportions
Old 24th March 2015
  #1
Lives for gear
 
🎧 10 years
Intensity Difference and Time Difference stereophony in about equal proportions

dear GS,

from "The stereophonic zoom" of Michael Williams :
http://microphone-data.com/media/fil...%20zoom-10.pdf

i read:
"for a given SRA one obtains minimum Angular Distortion by
using a combination of Intensity Difference
(Angle) and Time Difference (Distance)
stereophony in about equal proportions.
Angular
Distortion increases by a few degrees, with
systems using only Intensity Difference
(Distance = 0cm), and even more so with
systems using mostly Time Difference (Angle between microphones
= 0° or with spaced omnidirectional
microphones). "

Is this true??

so with fig 8 mikes I would best use these setups?

distance angle SRA
181 152 10
90 126 20
62 106 30
47 88 40
38 75 50
32 64 60
28 53 70
25 46 80
23 40 90
21 34 100
20 28 110
18 23 120
18 19 130
17 15 140
17 11 150
16 7 160
16 4 170
0 16 180

and what about using two pairs and SRA?
Old 24th March 2015
  #2
Lives for gear
 
🎧 10 years
Blumlein thought we used amplitude difference for mid and HF and time of arrival for LF
Being able to articulate the head is great for fore and aft calculations
Old 24th March 2015 | Show parent
  #3
Lives for gear
 
🎧 10 years
Quote:
Originally Posted by Rolo 46 ➡️
Blumlein thought we used amplitude difference for mid and HF and time of arrival for LF
Being able to articulate the head is great for fore and aft calculations
so we could use
MS for >1600 Hz
and add in AB for <800Hz?


EQ both pairs? or just mix them like that?
Old 24th March 2015
  #4
Lives for gear
 
🎧 10 years
Blumlein shuffled his MS array
Ive never done that
The MKH 30 is a mic ADB would have marvelled
Old 24th March 2015 | Show parent
  #5
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🎧 10 years
Quote:
Originally Posted by Rolo 46 ➡️
Blumlein shuffled his MS array
Ive never done that
The MKH 30 is a mic ADB would have marvelled
Ok but you can't get time of arrival differences with coincident setups?
Old 24th March 2015 | Show parent
  #6
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jimjazzdad's Avatar
 
🎧 10 years
Quote:
Originally Posted by monitor ➡️
so we could use
MS for >1600 Hz
and add in AB for <800Hz?


EQ both pairs? or just mix them like that?
As an amateur recordist of youth orchestra and wind ensemble / brass band, I found my way to the Remote Possibilities forum. Possessing neither the vast experience nor the mics that Roger has, my MS recordings seemed less than satisfactory - good imaging but not 'full'. Maybe this was due to to the mic placement, the hall...I don't know. I added a pair of omnis at ~ 40 cm. spacing to the MS pair (this is the so-called Boojum-Norman array often discussed in this forum). I have been very pleased with the improvement, especially in the low end. The spaced pair usually seems to end up 6 db or so below the MS pair. It is pretty 'adjustable' in post. I play with it until it sounds good. I have never found the need to EQ the pairs separately, but since you bring it up, I will have to experiment and see what it sounds like when applying a cross-over point to the two pairs...

And yes, wouldn't Blumlein marvel at all the toys we have today. But he would likely find much to rail against too.
Old 24th March 2015 | Show parent
  #7
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mpdonahue's Avatar
Quote:
Originally Posted by monitor ➡️
Ok but you can't get time of arrival differences with coincident setups?
The short answer is no.
All coincident systems rely on intensity differences and the dropoff of level caused by polar pattern to create a stereo field. The problem is that for a microphone to be directional there has to be a phase differential between the front and rear of the capsule diaphragm. At low frequencies the wavelength is very long and as a result there is virtually no differential between the front and back of the membrane. That is why if you look at the polar pattern vs. frequency all directional microphones become more omni as frequency descends. This causes low frequencies to be perceived without specific location/direction in coincident arrays.

Spaced omni arrays use time of arrival for higher frequencies and phase for lower frequencies to determine location and as such, the width of the array determines the perceived locations.
Quasi-coincident arrays (ORTF, NOS...) use a combination of these to arrive at their stereo pickup.
All the best,
-mark
Old 24th March 2015
  #8
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pkautzsch's Avatar
 
🎧 15 years
Quote:
Originally Posted by monitor ➡️
from "The stereophonic zoom" of Michael Williams :
http://microphone-data.com/media/fil...%20zoom-10.pdf

i read:
"for a given SRA one obtains minimum Angular Distortion by
using a combination of Intensity Difference
(Angle) and Time Difference (Distance)
stereophony in about equal proportions.
Angular
Distortion increases by a few degrees, with
systems using only Intensity Difference
(Distance = 0cm), and even more so with
systems using mostly Time Difference (Angle between microphones
= 0° or with spaced omnidirectional
microphones). "

Is this true??
It is true from a theoretical POV, and this approach is what setups like ORTF or NOS are based on. A bit of spacing and a bit of angle. These arrays are often called "near coincident" or "equivalent".
The theoretical downside of this is that you need directional mics for those setups. A directional mic can - physics! - never have a linear bass response. "True omnis", ie. pressure transducers, can and do. So if you want to use omnis for most "natural" sound and good representation of the room, you need to set them up spaced.

It Depends on music, hall, ensemble, and expectations. Knowing what the outcome should sound like is extremely helpful in choosing a mic setup.
Do you need great bass? Spaced pair.
Do you need pinpoint imaging? MS or XY.
Do you need a quick and unobtrusive setup because you have 20 minutes to get set? ORTF.

When you use two pairs, say XY and spaced, you should make sure the SRAs match. A spaced pair will spread the center a bit. So rather have the spaced pair's SRA a little smaller than the XY's if you want to use them equally. Carefully listen (on speakers!!!) if you get double imaging.
If the spaced pair is there to add a bit of spaciousness but will probably be mixed at a lower level than the XY, set it up wider.
Old 24th March 2015 | Show parent
  #9
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Bruce Watson's Avatar
 
🎧 10 years
Quote:
Originally Posted by pkautzsch ➡️
Do you need a quick and unobtrusive setup because you have 20 minutes to get set? ORTF.
Or my fav, a Boojum / JNorman / Faulkner phased array, ORTF and spaced omnis on the same stereo bar, capsules aligned. You can set this up before you leave for the gig (take the mics out for transport). When you get to the gig, add mics and cables and run up the stand. Done. Well, done with that part anyway.
Old 3rd April 2015
  #10
Lives for gear
 
🎧 10 years
thanks for all the helpful advice guys!

well mostly I hear about the fig 8s being used
in 90° XY and 20cm AB.

But what about angling spaced fig 8 (ribbons)?
for example 25 cm and 40 ° angle.
this would give a 87° SRA.

or second scenario:

MS or Blumlein ribbons close, SRA = 75
to combine with omnis AB 85cm SRA=75

third:

MS or Blumlein ribbons close, SRA = 75
to combine with omnis a couple of meters
further away so it matches the SRA of the MS pair?

which omnis are best to place really in the reverberant field?
schoeps MK3? anybody uses this?
Old 16th April 2015
  #11
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🎧 10 years
bump
Old 16th April 2015 | Show parent
  #12
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Roland's Avatar
 
2 Reviews written
🎧 15 years
Quote:
Originally Posted by mpdonahue ➡️
The short answer is no.
All coincident systems rely on intensity differences and the dropoff of level caused by polar pattern to create a stereo field. The problem is that for a microphone to be directional there has to be a phase differential between the front and rear of the capsule diaphragm. At low frequencies the wavelength is very long and as a result there is virtually no differential between the front and back of the membrane. That is why if you look at the polar pattern vs. frequency all directional microphones become more omni as frequency descends. This causes low frequencies to be perceived without specific location/direction in coincident arrays.

Spaced omni arrays use time of arrival for higher frequencies and phase for lower frequencies to determine location and as such, the width of the array determines the perceived locations.
Quasi-coincident arrays (ORTF, NOS...) use a combination of these to arrive at their stereo pickup.
All the best,
-mark
I, of course, agree with all the above, however, I have found that with surround recordings, you can achieve better/more? perceived bass performance, even when using a coincidence array, though not directional information. Equally the bass, directional information, even on spaced arrays, would likely be inaccurate, due to listening environments physical size (or at least most of them).
Old 3 weeks ago | Show parent
  #13
Lives for gear
 
🎧 10 years
Quote:
Originally Posted by monitor ➡️
bump
Can we give monitor a '6 years-on bump' on his posting....any thoughts on optimal pairings of central Blumlein or M/S with spaced omnis (for equivalent SRA) ?
Old 3 weeks ago
  #14
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emrr's Avatar
 
24 Reviews written
🎧 10 years
I’ve done satisfactory experiments with blumlein MKH 30’s and AB60ish MKH 20’s, using a complementary lpf hpf approach. I preferred the result to either alone, it seemed to confirm the perceptual theories. But then, I had bias having done the test. My tests were with thunderstorms, and I also used the approach to make some reverb IR’s.
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