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Author Topic: Don't have a wide mic bar? Give PAS with figure 8's a try  (Read 5655 times)

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Offline MattH

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Re: Don't have a wide mic bar? Give PAS with figure 8's a try outdoors
« Reply #15 on: July 09, 2016, 12:27:21 PM »
Here is my first experiment with PAS figure 8's. I was FOB about 2/3 back and spaced the mics 30 cm. I realize this is closer and wider spaced than OP's suggestion but I wanted to try it anyway. I'm glad I did ;D

http://bt.etree.org/details.php?id=587549

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Offline Gutbucket

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Re: Don't have a wide mic bar? Give PAS with figure 8's a try outdoors
« Reply #16 on: July 11, 2016, 09:41:35 AM »
Hi Matt, thanks for the link.. just jumped on the torrent with the intention of listening tonight. I'm somewhat confused by your etree note mentioning "PAS Blumlein", which I interpret as "coincident fig-8s pointed at the PA (no spacing between mics)", yet above you mention a 30cm spacing. When you say "closer and wider" do you mean recording from a position close to the stage with the microphones spaced apart more widely, or a relatively wider angle between mics in order to point them directly at the PA stacks?  What do you estimate the angle between the two microphones to have been?


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Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<<

Offline MattH

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Re: Don't have a wide mic bar? Give PAS with figure 8's a try outdoors
« Reply #17 on: July 12, 2016, 09:06:39 AM »
Hi Matt, thanks for the link.. just jumped on the torrent with the intention of listening tonight. I'm somewhat confused by your etree note mentioning "PAS Blumlein", which I interpret as "coincident fig-8s pointed at the PA (no spacing between mics)", yet above you mention a 30cm spacing. When you say "closer and wider" do you mean recording from a position close to the stage with the microphones spaced apart more widely, or a relatively wider angle between mics in order to point them directly at the PA stacks?  What do you estimate the angle between the two microphones to have been?

I was closer in that I was FOB and not at the SBD or behind. I was wider in that the mics were separated more than the 18 cm you suggested. It was closer to 30 cm due to my mic bar and the way my LD's mount. I would estimate the angle was about 60 degrees.

I feel like I got something sort of Blumlein-like in it's "airiness"
mics: Soundfield ST450, JW mod Milab VIP-50's, Milab VM-44 Links (Matched Cards, Matched S-Cards), BR mod Nak 700's
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Offline Gutbucket

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Re: Don't have a wide mic bar? Give PAS with figure 8's a try outdoors
« Reply #18 on: July 12, 2016, 11:35:26 AM »
The spacing you used is pretty much right in line with what this proposed method suggests as optimal for that particular mic angle.

The closer spaced example in the first post of the thread (fig-8's spaced about 7" (~18cm) and angled ~50 degrees apart) was mean to be something doable with a typical mic bar width, for a what I suspect will be a common PAS angle.  I chose that particular example because it represents an improvement over using cardioids with the same spacing and angle by just switching the mics to bi-directionals.  In that case the 50 degree angle between microphones and the resulting SRA of 90 degrees doesn't actually match up with each other, so it's not an optimized PAS configuration in terms of the Improved PAS idea I initially pitched here at TS a few years back as typically implemented using cardioids and supercards.  It's just something close to what tapers are already doing for PAS.  I later later realized that the fig-8 pattern provides an advantage at narrow mic angles in requiring somewhat less spacing which lead to this thread.  Your spacing is close to the Improved PAS concept of matching the SRA and mic angle by modification of the spacing.

With the Stereo Zoom, the correct amount of spacing between the two mics corresponds to the angle between them (or vice-versa), and in the case of PAS, the angle between mics is going to be the angle between the stacks, or at least pretty close to it.  Attached below is the same Michael William's Stereo Zoom table for a pair of figure 8s I linked in the first post of the thread, on which I've added some red dots along a red line.  The red line indicates all the combinations of mic spacing and angle where the angle between the mics is the same as the the stereo recording angle (SRA), just as we'd like it to be for PAS.  The appropriate spacing between mics can then be read from the bottom of the graph below where the red line intersects with and the horizontal line indicating the angle between mics:


For the left-most red dot, the angle between mics is 80 degrees and the spacing between mics is zero or coincident.  That combination produces an SRA of +/- 40 degrees or 80 degrees total, which is the same as the angle between mics. (This is pretty much the standard coincident Blumlien setup*)

For the second red dot from the left, the angle between mics is 70 degrees and the spacing between mics is ~19cm. That combination produces an SRA of +/- 35 degrees or 70 degrees total, same as the angle between mics.

For the third red dot from the left, the angle between mics is 60 degrees and the spacing between mics is ~35cm. That combination produces an SRA of +/- 30 degrees or 60 degrees total, same as the angle between mics.

The fourth red dot is just off the edge of the graph, but indicates an angle between mics of 50 degrees and a spacing of ~55cm, for an SRA of +/- 25 degrees or 50 degrees total.
And so forth..


According to this figure-8 PAS hypothesis, the spacing you used is very close to the 60 degrees ~35cm combination and pretty much exactly what you'd want for that particular mic angle.
« Last Edit: July 13, 2016, 09:04:59 AM by Gutbucket »
musical volition > vibrations > voltages > numeric values > voltages > vibrations> virtual teleportation time-machine experience
Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<<

Offline Gutbucket

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Re: Don't have a wide mic bar? Give PAS with figure 8's a try outdoors
« Reply #19 on: July 12, 2016, 12:56:24 PM »
*A foot note on Blumlein config, Williams, and my own experience..

For the left-most red dot, the angle between mics is 80 degrees and the spacing between mics is zero or coincident.  That combination produces an SRA of +/- 40 degrees or 80 degrees total, which is the same as the angle between mics. (This is pretty much the standard coincident Blumlien setup*)

The standard traditional Blumlein setup of coincident figure-8's crossed at right angles to each other is typically used with all sound sources placed comfortably inside the 90 degree front quadrant.  Interpreted in terms of the Stereo Zoom, the instruction for making sure all sources fit "comfortably inside the 90 degree front quadrant" is acknowledgement that the total SRA is somewhat less than 90 degrees.  William's table indicates an SRA of about +/- 35 degrees or 70 degrees total.  Also notice that on William's graph, 90 degrees with zero spacing, lies within the upper grey shaded area.  The grey areas indicate combinations with increased angular distortion near the edges or center of the playback image.

For those reasons, a slightly narrower angle of 80 degrees between coincident fig-8's and the resulting matching 80 degree SRA angle, represents something of an "improvement on standard Blumlein".  And indeed over the years I've found I've found I prefer a slightly narrower angle than 90 degrees for Blumlein, partly because it provides a somewhat more solid center.

Playing with Image Assistant on the hauptmikrofon website http://www.hauptmikrofon.de/stereo-3d/image-assistant/ima-3-app, one can see the effects on the curves in reducing the angle between coincident 8's by 10 degrees, or by leaving the angle at 90 degrees and spacing the mics apart slightly.


I feel like I got something sort of Blumlein-like in it's "airiness"

Unfortuantely I didn't get to listen last night, hope to tonight..
« Last Edit: July 12, 2016, 02:40:59 PM by Gutbucket »
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Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<<

Offline Gutbucket

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Re: Don't have a wide mic bar? Give PAS with figure 8's a try outdoors
« Reply #20 on: July 13, 2016, 09:26:49 AM »
 I like it.  Open, clear, natural.   The low frequency roll-off of the 8 pattern can be compensated for pretty easily.  Diffuse field correlation sounds significantly low (good), which helps it sound enveloping and not closed in.  Some listeners might prefer a stronger and more monophonic center, which could be achieved with slightly less spacing or the same spacing but slightly less angle.

I quite enjoyed listening to this.  Did you notice any significant difference in the pickup of audience noise immediately nearby verses what you expected?  There is of course lots of rearward sensitivity due to the rear lobes of the bi-directional pattern, yet the overlaping null planes of the two patterns should significantly reduce pickup of noise arriving from immediately below (your noisy self  ;)), and somewhat to the sides depending on mic angle.

Thanks for trying this out and posting the link!
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Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<<

Offline EmRR

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Re: Don't have a wide mic bar? Give PAS with figure 8's a try outdoors
« Reply #21 on: December 21, 2017, 10:24:48 PM »
For those reasons, a slightly narrower angle of 80 degrees between coincident fig-8's and the resulting matching 80 degree SRA angle, represents something of an "improvement on standard Blumlein".  And indeed over the years I've found I've found I prefer a slightly narrower angle than 90 degrees for Blumlein, partly because it provides a somewhat more solid center.

I've found MS matrix of a pair of fig-8's (same pattern as 90º Blumlein, if mixed correctly) to give a more solid center than Blumlein in many cases, and better retention of highest frequencies when summed towards mono.  80º or less could be very useful with some distances and PA widths.  I need to try the Faulkner approach.   

I am liking, at least for my purposes, the flatter than normal bottom response of the MKH 30's and MKH 800 Twin, much more like what I get from ribbon mics.  Big, non-stealth mics though. 

Offline noahbickart

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Re: Don't have a wide mic bar? Give PAS with figure 8's a try outdoors
« Reply #22 on: December 22, 2017, 09:16:25 AM »
^^^^^^^^^

For the record Blumlein himself used two figure 8 microphones in a M/S array.....
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Offline EmRR

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Re: Don't have a wide mic bar? Give PAS with figure 8's a try outdoors
« Reply #23 on: December 22, 2017, 09:30:12 AM »
Yes, so I hear. It would seem one of the strongest arguments to make to the person skeptical of MS. 

Offline Gutbucket

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Re: Don't have a wide mic bar? Give PAS with figure 8's a try outdoors
« Reply #24 on: December 22, 2017, 09:30:31 AM »
There is much to be said for Mid/Side getting the center correct.  The mid mic points directly forward, taking best advantage of the mid microphone's on-axis response and minimizing off-axis response irregularities for the center response.  Even though PAS it's not (usually) coincident, it's the same in that way - each mic on-axis with the PA speaker on each side.

Also there should be less response variation due to minor phase cancellations at very high frequencies in the mono sum.  With Mid/Side Blumlein the Side signal cancels out in the mono sum, and what remains is the signal from the Mid microphone alone.  With X/Y Blumlein the Side signal also cancels out in the mono sum, but the remaining Mid signal is not just the signal from one mic alone but the common signal of both mics in combination, with slight response variations due phase differences from not quite perfect coincidence above some frequency.
musical volition > vibrations > voltages > numeric values > voltages > vibrations> virtual teleportation time-machine experience
Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<<

Offline Gutbucket

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Re: Don't have a wide mic bar? Give PAS with figure 8's a try outdoors
« Reply #25 on: December 22, 2017, 09:34:43 AM »
For the record Blumlein himself used two figure 8 microphones in a M/S array.....

Don't forget he started with head-spaced baffled omnis. Before figure 8 pattern microphone was available to him.

Yes, so I hear. It would seem one of the strongest arguments to make to the person skeptical of MS.

I don't follow, why so?
musical volition > vibrations > voltages > numeric values > voltages > vibrations> virtual teleportation time-machine experience
Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<<

Offline dactylus

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Re: Don't have a wide mic bar? Give PAS with figure 8's a try outdoors
« Reply #26 on: December 22, 2017, 02:45:05 PM »
Here is my first experiment with PAS figure 8's. I was FOB about 2/3 back and spaced the mics 30 cm. I realize this is closer and wider spaced than OP's suggestion but I wanted to try it anyway. I'm glad I did ;D

http://bt.etree.org/details.php?id=587549

Is there a chance that any of you could seed this torrent posted on bt.etree for 30 minutes?  I should be able to snag it in that amount of time.  Thanks!!

Snagged it!!  Thanks!
« Last Edit: December 23, 2017, 09:39:35 AM by dactylus »
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Offline EmRR

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Re: Don't have a wide mic bar? Give PAS with figure 8's a try outdoors
« Reply #27 on: December 22, 2017, 09:06:05 PM »

Yes, so I hear. It would seem one of the strongest arguments to make to the person skeptical of MS.
I don't follow, why so?

In that Blumlein's use of MS authenticates the legitimacy of a technique that a lot of people don't believe can work, because they haven't researched it or tried it.  If you need an argument for a skeptic of MS, it seems the best one to me....if they know anything about Blumlein.....hope that makes sense. 

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Re: Don't have a wide mic bar? Give PAS with figure 8's a try outdoors
« Reply #28 on: December 22, 2017, 11:44:04 PM »
Dug into the pattern charts a bit.  I see that MS with two figure 8 gives you the ability to virtually change the angle of a pair of Blumlein figure 8, after the fact, with a change in the blend.  Another win.   When you change Blumlein width with panning you only change the presented width between playback speakers, as opposed to a virtual pattern repositioning.  This would seem to change the expected relationship of the combined pattern nulls, and explains the changes in the high frequencies.  It ideally shouldn't be panned anywhere between outputs at all.  All theories with ideal poor patterns across all frequencies, of course.  The real world will treat us differently. 

Offline Gutbucket

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Re: Don't have a wide mic bar? Give PAS with figure 8's a try outdoors
« Reply #29 on: December 26, 2017, 04:26:38 PM »

Yes, so I hear. It would seem one of the strongest arguments to make to the person skeptical of MS.
I don't follow, why so?

In that Blumlein's use of MS authenticates the legitimacy of a technique that a lot of people don't believe can work, because they haven't researched it or tried it.  If you need an argument for a skeptic of MS, it seems the best one to me....if they know anything about Blumlein.....hope that makes sense.

Yes, quite.  I'd misread your statement as stating the opposite (overlooked the 2nd "to"), reading it as stating the argument would make a person skeptical of Mid/Side, rather than it would make for a good argument to convince someone otherwise skeptical of Mid/Side.
musical volition > vibrations > voltages > numeric values > voltages > vibrations> virtual teleportation time-machine experience
Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<<

 

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