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Gear / Technical Help => Microphones & Setup => Topic started by: Gutbucket on April 03, 2014, 09:57:14 PM

Title: Improved PAS setups - better imaging with higher direct-sound/reverberant ratio
Post by: Gutbucket on April 03, 2014, 09:57:14 PM
I've reworked the Point At Stacks (PAS) microphone configuration setup table I posted a few years ago to make it more useful for advanced tapers, rather than simply consisting of a few spacing recommendations for the quick-and-easy PAS setup.

The table takes PAS and applies the Stereo Zoom concept and data to suggest a few appropriate microphone spacings determined by whatever angle you end up with between microphones when you point them directly at the PA speakers.  I’ll explain where, why and how to use it in following posts. Here it is below as a GIF.  I’ve also attached it as a PDF.

[edit- first, here's a copy of the original simplified table with only two columns (calculated using cardioids, the shaded row is DIN)]-
(http://taperssection.com/index.php?action=dlattach;topic=153112.0;attach=105743;image)

[and below is the new extended table with several options and information for each PAS angle]-

[edit again- Try figure 8's in PAS outdoors.  They require the least spacing between mics of any pattern, allowing even narrow-width mic bars to work).  More here- http://taperssection.com/index.php?topic=177050.0]

[extended table GIF and PDF edited to correct a typo]
Title: Re: PAS table (printable) - maximise direct/reverberant pickup & retain good imaging
Post by: Gutbucket on April 03, 2014, 09:58:14 PM
How to use the table-

1) Determine the angle between the PA speakers as seen from the recording position.

2) Consult the table. Find the angle between microphones in the left column.

3) Choose one of the four spacings indicated in the Mic spacing column immediately to the right.  The safe bet if you don’t know which to pick is the one in the grey row. 

4) Setup the mics with that spacing. If your mic bar doesn’t let you achieve that particular spacing, try to get the microphones somewhere within the range of spacings shown for that microphone angle. If you can’t do that, just get as close as you can.

5) Record. Enjoy the show. Go nuts. Go home.

6) Play it back and listen.  If you prefer a more narrow sounding presentation with the on-stage and PA sound more tightly grouped in the middle between the speakers, choose a wider SRA the next time (which means a narrower microphone spacing).  If you’d prefer something that sounds wider, choose a narrower SRA the next time (a wider microphone spacing).  Once you determine your personal preference you can always default to the same row, or you can pick and choose between them to suit the situation.

That’s it.
Title: Re: PAS table (printable) - maximise direct/reverberant pickup & retain good imaging
Post by: Gutbucket on April 03, 2014, 09:59:42 PM
The why and where-
 
The table is based on data from the excellent  sengpielaudio (http://www.sengpielaudio.com/Visualization-ORTF-E.htm) page which has been linked here at TS many times before.  It’s a great tool.

The inspiration to revisit this was deadheadcorey's recent thread titled- PAS/POoS (http://taperssection.com/index.php?topic=167412.msg2086141#msg2086141) which got me thinking again about why the PAS configuration makes a lot of sense in difficult recording situations such as rooms with bad sounding ambiences, overloud obnoxious audiences, and recording positions which are further away from the stage and PA than we'd choose, because it helps maximize the direct/reverberant pickup from a given location.  In simple terms that means it focuses as much as possible on the sound from the PA and band on stage (the direct sound), and less on the sound arriving from everywhere else (the reverberant, ambient sound). 

The most effective way to maximize the direct sound and minimize the reverberant room sound is to move closer to the source.  The extreme is stack taping where the majority of the sound arriving in the recording position comes directly from the PA and very little of it is reverberant room sound (at least in proportion to the PA sound).  The opposite extreme is the far back of an arena, where the situation is reversed and most of the sound arriving at the recording position is reverberant room sound, swamping the direct sound.

PAS using supercardioids maximizes the proportion of direct sound picked up verses the reverberant sound as much as possible from a given recording location.  It isn’t a substitute for finding the optimal recording location and it certainly can’t make the back of the room sound like the front.  It simply makes the best of a mediocre situation. From a good recording position in an excellent sounding room, other configurations may be more appropriate, but using the table won’t make a bad recording.  It’s entirely possible to have a direct/reverberant ratio that’s too high.  That’s one problem with a stack tape or a straight SBD, it’s mostly direct sound that often doesn’t have enough good reverberant room information and sounds not so 'live' but rather lifeless.

The problem with the typical PAS setup is that it doesn’t indicate how much spacing is appropriate between the two microphones. Most tapers simply use whatever spacing their mic bar provides. At the narrow microphone angles typical of PAS, the spacing between microphones is often not enough to achieve good playback imaging which evenly fills the space between speakers with phantom images (or sounds open and as if ‘you are there again’ over headphones) and provides an appropriately wide and involving audio illusion with the audience applause wrapping around the listener.


PAS is a dedicated concert tapers microphone configuration and this table quantifies it to make it a more valuable tool with improved stereo imaging.

Here's a link to the original thread discussing the first go-round at this, which partly works through the process of developing the table- !!Stereo Zoom simplified for PAS!! (http://taperssection.com/index.php?topic=153112.msg1938190#msg1938190)

This new version of the table expands on it by using supercardioid microphones as a starting point. Cardioid mics will work too, and probably image similarly for the direct sound, the data doesn’t change that much substituting that pattern (notice that the same angles on the simple table which is  based on cardioids, and the new extended table which is based on supercardioids have spacings that differ by only about 1cm), but using supercardioids helps maximize the direct/reverberant pickup ratio.
Title: Re: PAS table (printable) - maximise direct/reverberant pickup & retain good imaging
Post by: Gutbucket on April 03, 2014, 10:00:51 PM
More details on each step and on the other stuff in the table-

1) With PAS, the angle between PA speakers is always the same as the angle between microphones.  Using supercardioid (or hypercardioid) pattern microphones and pointing them directly at the PA is what maximizes pickup of the direct sound component as much as possible from the recording position.  The first step after choosing a recording position is to measure that angle.  Since they are the same, you can either meausure the angle between PA speakers or the angle between microphones.  There are a few ways to measure.   I’ve learned to measure distant angles quickly and relatively accurately by using what I call the “backyard astronomer / poor sailor method”.  A balled fist held at arms length and viewed through one squinted eye covers approximately a 10 degree arc.  Practice measuring a few known angles and you can perfect it pretty quickly.  I need to kind of stick my thumb knuckle out a bit to get a full 10 degrees.  Yes it looks funny when doing it.  Smart-phone apps now exist which make measuring angles easily without looking like you are shaking your fist at the stage.

Alternately you might simply go ahead and set up the microphones, point them directly at the PA speakers, measure the angle between the microphones themselves, then readjust their spacing once you determine what that should be.  You can measure microphone angles directly by whiping out a protractor or using an angleometer, use some creative oragami folding techniques to estimate angles, or a smart-phone app.

2) Consulting the table- If you understand the Stereo Zoom concept, here’s a few things going on here: The PA angle is the Orchestra Angle and on this table that’s always the microphone angle as well.. that’s what makes it PAS.  The grey rows provide a Stereo Recording Angle which is 10 degrees wider than the Orchestra Angle (and the stacks), which is generally a good starting point.

The options in the other rows for the same microphone angle are SRAs which are 20 degrees wider than the PA speakers, the same width as the PA and 10 degrees narrower than the PA.  That information and the total SRA angle are indicated in the columns to the right of the one indicating the closest “standard” mic setup, which is just for reference.  The only standard setup which is exact is DINa (which maybe only a standard to tapers and not the rest of the world anyway), the others are approximate.  Yes, it is true that ORTF is only ORTF if it uses small diaphram cardioids which have well behaved polar patterns angled 110 degrees apart and spaced 17cm.  The squiggly line in front indicates “approximately” and the indication simply provides a general point of reference many users will be familiar with.

3) Playback width is how far the sound sources within the SRA window extend outwards from the center towards the speakers on playback.  It describes the relationship between the SRA and the “playback window between the two speakers”. If it’s 100%, sounds originating from the outer edges of the SRA should spread out to the speaker locations, if less than 100% the outer edges of the SRA won’t extend all the way out to the speaker locations and things will be more tightly grouped in the middle.

4) The Level and Time delta columns indicate what proportion of the phantom stereo imaging is based on level differences between channels due to the angle of the microphones and how much is due to time of arrival differences due to the spacing between them.

5) Notice how wide the microphone spacings become with narrow microphone angles.  As the angle between microphones gets increasingly narrow, the level differences between them decrease rapidly and they begin behave more like omnis with regards to stereo imaging, though not like omnis at all in terms of direct/reverberant pickup ratio.  It might be difficult to setup the wide spacings indicated on the table due to practical considerations such as the limited length of the microphone mounting bar, but since decent spaced omni recordings can be made with less wide spacings it may be acceptible for you to err towards spacings which are somewhat less wide than what the table suggests in those situations.  However I doubt I’m the only one who likes omnis a few meters wide when recording from far enough away that the angle between PA speakers is only measures about 40 degrees wide or so.  When you consider it from that perspective, setting up supercardioids about a meter apart with a 40 degree angle between them will begin to seem much more reasonable than it might have at first glance, even if it’s not always so easy to achieve. 
Title: Re: PAS table (printable) - maximise direct/reverberant pickup & retain good imaging
Post by: MIQ on April 03, 2014, 11:53:54 PM
Hi Gut

Excellent post on applying the Stereo Zoom concept as usual. Thank you for posting this!

I think there may be a small cut and paste error in the 50 degree row.

(Trying to walk a fine line between shameless self promotion and adding useful info) >:D
Like you wrote there are smartphone apps that can increase the choices beyond the 10 degree increments you've listed. One nice thing about the Stereo Mic Tools app we developed is that it allows you to measure the angle of your mics when pointed at the stacks in the "bombsight" screen then quickly flip to the recording angle calculator screen to determine the exact mic spacing that makes the recording angle match the mic angle. Also we provide selection of many popular directional mic patterns including the cardioid and supercard patterns you've shown in these tables. Of course a printed copy of the table you've created will work even when your iPhone battery is dead.  ;D

FYI your original post on this is the first reference listed in the "info" page of the Stereo Mic Tools app. Much respect.  :)

Miq
Title: Re: PAS table (printable) - maximise direct/reverberant pickup & retain good imaging
Post by: deadheadcorey on April 04, 2014, 11:37:38 AM
thanks for putting this together gutbucket!
Title: Re: PAS table (printable) - maximise direct/reverberant pickup & retain good imaging
Post by: Ultfris101 on April 04, 2014, 12:13:00 PM
this is great. many thanks for the effort. I need to get much wider spreads in the small, narrow club where I typically tape from the back of the room near the soundboard. going to try that tonight.

 :coolguy:
Title: Re: PAS table (printable) - maximise direct/reverberant pickup & retain good imaging
Post by: Gutbucket on April 04, 2014, 01:25:55 PM
Thanks for the thanks. 

There is one thing I'll ask of those of you who use this which will help refine it-
Once you've used this enough to determine which SRA width choice you like most of the time (+20°, +10°, same as the stack angle, -10°), please post here with feedback to let me know your general preference.  And I mean your preference for the resulting playback results, rather than those based on setup constraints like whatever your mic bar width happens to allow.

That question is something I've wondered about and it can only be determined through trial and error.  The +20° to -10° range is a simply a best guess at an appropriate range of options.  The best answer may be mostly personal preference, may be situation dependant, or a combination of things.  I may add a row for +30 as well, to extend the options to less wide spacings which are closer to typical PAS setup as commonly practiced, and which can be more easily done with less wide bars, even though I suspect that will be a wider SRA (and narrower resulting image) than is optimal.  I doubt there is any need to go to finer than 10° angular increments.  Similarly the tolerance on the fractional centimeter and inch measurements on the table are more precise than they need to be.  Get it to within an inch or so and that's probably close enough, especially at wider spacings.

Thanks to Michael Williams for the Stereo Zoom data and research.  This is just a re-interpretation of that to present it in a way that's specific to what we do.
Title: Re: PAS table (printable) - good imaging with high direct/reverberant pickup ratio
Post by: dyneq on July 13, 2014, 05:48:02 PM
Hey All,

I'd like to experiment with this method and had a couple of questions:

To those of you who have tried this in the field: what method did you use to determine the angle between the PA speakers? The chart has 10 degree increments, and that seems like a tricky distinction to make in the field. Since the spacing is quite different for the different angles, I'd want to try and get fairly close to the actual angle, especially as I experiment to find my spacing preferences (as repeatable as possible).

Anyone experimented with it outdoors? If so, which part of the spacing spectrum did you run/prefer?

I plan to try this at Rockygrass where it was a gentle slope from the OTS down to the stage (not a well-defined bowl). After last September's flooding, it may look completely different this year.
Title: Re: PAS table (printable) - good imaging with high direct/reverberant pickup ratio
Post by: Gutbucket on July 14, 2014, 10:25:34 AM
questions:

To those of you who have tried this in the field: what method did you use to determine the angle between the PA speakers? The chart has 10 degree increments, and that seems like a tricky distinction to make in the field. Since the spacing is quite different for the different angles, I'd want to try and get fairly close to the actual angle, especially as I experiment to find my spacing preferences (as repeatable as possible).

[self quote]
There are a few ways to measure.   I’ve learned to measure distant angles quickly and relatively accurately by using what I call the “backyard astronomer / poor sailor method”.  A balled fist held at arms length and viewed through one squinted eye covers approximately a 10 degree arc.  Practice measuring a few known angles and you can perfect it pretty quickly.  I need to kind of stick my thumb knuckle out a bit to get a full 10 degrees.  Yes it looks funny when doing it.  Smart-phone apps now exist which make measuring angles easily without looking like you are shaking your fist at the stage.

Alternately you might simply go ahead and set up the microphones, point them directly at the PA speakers, measure the angle between the microphones themselves, then readjust their spacing once you determine what that should be.  You can measure microphone angles directly by whiping out a protractor or using an angleometer, use some creative oragami folding techniques to estimate angles, or a smart-phone app.
[/self quote]
Title: Re: PAS table (printable) - good imaging with high direct/reverberant pickup ratio
Post by: Ultfris101 on July 14, 2014, 10:43:01 AM
I've been using the outstretched fist method. Never actually measured to see how close it is but I've heard it mentioned a few times.
Title: Re: PAS table (printable) - good imaging with high direct/reverberant pickup ratio
Post by: voltronic on July 14, 2014, 11:01:03 AM
The best tool I have found for this is a compass bearing app with camera overlay.  You point center, note the bearing.  Pan to the far left or right of your included angle, note the second bearing.  Couldn't be easier.  I have found that the "large viewfinder" overlay (second image) is the most accurate. 
https://play.google.com/store/apps/details?id=com.appyhand.bearingcompass (https://play.google.com/store/apps/details?id=com.appyhand.bearingcompass)
Title: Re: PAS table (printable) - good imaging with high direct/reverberant pickup ratio
Post by: dyneq on July 14, 2014, 12:06:39 PM
Thanks, folks!

Since I'm after repeatability as I test/tweak this technique, I'll give the app a try. I'm the same way about cooking; follow the recipe as it is written the first few times, then adjust to my tastes!
Title: Re: PAS table (printable) - good imaging with high direct/reverberant pickup ratio
Post by: adrianf74 on July 14, 2014, 01:33:48 PM
The best tool I have found for this is a compass bearing app with camera overlay.  You point center, note the bearing.  Pan to the far left or right of your included angle, note the second bearing.  Couldn't be easier.  I have found that the "large viewfinder" overlay (second image) is the most accurate. 
https://play.google.com/store/apps/details?id=com.appyhand.bearingcompass (https://play.google.com/store/apps/details?id=com.appyhand.bearingcompass)

Thanks!

I've been using "Smart Tools" in my android phone for some time (paid app with a whole bunch of stuff in it) but they have a free "Smart Compass" app which is part of that.  Works really well, too.  I'm still gonna give the AB Bearing app a shot next time I'm out.

Smart Compass is here:
https://play.google.com/store/apps/details?id=kr.sira.compass
Title: Re: PAS table (printable) - good imaging with high direct/reverberant pickup ratio
Post by: voltronic on July 14, 2014, 02:09:33 PM
The best tool I have found for this is a compass bearing app with camera overlay.  You point center, note the bearing.  Pan to the far left or right of your included angle, note the second bearing.  Couldn't be easier.  I have found that the "large viewfinder" overlay (second image) is the most accurate. 
https://play.google.com/store/apps/details?id=com.appyhand.bearingcompass (https://play.google.com/store/apps/details?id=com.appyhand.bearingcompass)

Thanks!

I've been using "Smart Tools" in my android phone for some time (paid app with a whole bunch of stuff in it) but they have a free "Smart Compass" app which is part of that.  Works really well, too.  I'm still gonna give the AB Bearing app a shot next time I'm out.

Smart Compass is here:
https://play.google.com/store/apps/details?id=kr.sira.compass

Very cool!  It does the same thing as the AR Bearing Compass app, but looks a bit slicker.  Thanks!
Title: Re: PAS table (printable) - good imaging with high direct/reverberant pickup ratio
Post by: Ultfris101 on July 14, 2014, 02:47:56 PM
I totally forgot about the Mic Tools app! Yes, the performer's angle measurement tool is great! Just used it for the first time a few weeks ago.
Title: Re: PAS table (printable) - good imaging with high direct/reverberant pickup ratio
Post by: MIQ on July 16, 2014, 03:02:14 AM
Thanks Ultfris101!

We just added that functionality to the Stereo Mic Tools App in the latest release.     ;D

-Miq
Title: Re: PAS table (printable) - good imaging with high direct/reverberant pickup ratio
Post by: voltronic on July 16, 2014, 07:19:52 AM
Thanks Ultfris101!

We just added that functionality to the Stereo Mic Tools App in the latest release.     ;D

-Miq

Any consideration for an Android version?
Title: Re: PAS table (printable) - good imaging with high direct/reverberant pickup ratio
Post by: MIQ on July 16, 2014, 03:11:58 PM
Sorry Voltronic coding for iOS is enough fun for us.

-Miq
Title: Re: PAS table (printable) - good imaging with high direct/reverberant pickup ratio
Post by: adrianf74 on July 17, 2014, 07:22:10 AM
Sorry Voltronic coding for iOS is enough fun for us.

-Miq

Android gets no love.  Have no Apple products in my household and am not about to start now.  I'll just stick to the table as a graphic on my phone and the compass -  does the job perfectly.  Now if only my SGC clips played nicely with my couplings, I'd be happy.
Title: Re: PAS table (printable) - good imaging with high direct/reverberant pickup ratio
Post by: MIQ on July 18, 2014, 02:29:59 PM
Hi adrianf,

That sounds like a solid way of doing it. We are just happy that more people are applying the Stereo Recording Angle approach to setting up their mics. As with most stuff, there are lots of ways to get there. 

Miq
Title: Re: PAS table (printable) - good imaging with high direct/reverberant pickup ratio
Post by: Gutbucket on July 18, 2014, 02:39:35 PM
Royal we?  ;)
Title: Re: PAS table (printable) - good imaging with high direct/reverberant pickup ratio
Post by: MIQ on July 18, 2014, 10:11:53 PM
Royal we?  ;)

 :D
I always say "we" when I write about the app because there are two of us working on it.  My buddy Rob writes all the code.  I should realize that's not apparent.  :facepalm:

Rob and I are happy people are applying the concepts regardless of the process they use.  Our app just pulls together a few tools in one place to make it a little more streamlined.

Miq

 
Title: Re: PAS table (printable) - good imaging with high direct/reverberant pickup ratio
Post by: carlbeck on August 09, 2014, 10:33:31 AM
As always Gutbucket, great job on the write up & thanks for making me open my eyes to different techniques. I ran my AKG's DINa & my Telefunkens PAS last night on the same stand, I'm converted now. The DINa is a fine recording but when I switch to the PAS I can hear less room, better impact & the same soundstage without the extra "ambiance" of the room. It's an eye opening experience & as you stated in one of your threads regarding this subject, why get a great imaging recording of room reverb? PAS still gave me great imaging with better impact, thanks! As a side note, I can't believe how much more information there is on this site vs when this place was in its infancy, kudos to all!
Title: Re: PAS table (printable) - good imaging with high direct/reverberant pickup ratio
Post by: Gutbucket on August 09, 2014, 04:23:50 PM
Hey thanks, Carl.  And thanks for posting here with your real-word feedback.

Of course I really want it all, including good ambient/reverberant imaging too!  It's just that, that stuff is just further down the list of what's most important and this helps shuffle the priorities around.
Title: Re: PAS table (printable) - good imaging with high direct/reverberant pickup ratio
Post by: huskerdu on August 14, 2014, 07:14:04 PM
This is awesome...thanks!
Title: Re: PAS table (printable) - good imaging with high direct/reverberant pickup ratio
Post by: Cobiwan on August 15, 2014, 10:08:34 PM
Any advice on running Nak CP-4s PAS? What spacing should be used?
Title: Re: PAS table (printable) - good imaging with high direct/reverberant pickup ratio
Post by: carlbeck on August 16, 2014, 07:42:33 AM
Any advice on running Nak CP-4s PAS? What spacing should be used?
The spacing used between capsules is determined by the angle required to PAS (point at the stacks or as close as possible) also the nice thing is that even if your mic bar isn't wide enough to achieve the desired angle you will still produce good results. All of this new found knowledge has me on a buying spree, I now have three new stereo bars in different widths to allow me to get the wide spacing preferred with the angles that PAS requires. Not to thread jack but look at the thread "New Rode stereo bar"
Title: Re: PAS table (printable) - good imaging with high direct/reverberant pickup ratio
Post by: Cobiwan on August 16, 2014, 01:38:30 PM
So you're saying PAS spacing is same for shotguns as it is for cardiods?
Title: Re: PAS table (printable) - good imaging with high direct/reverberant pickup ratio
Post by: Gutbucket on August 16, 2014, 06:03:10 PM
Here's the conceptual aspect of it-

The more directional the microphone's pickup pattern is, the less spacing is required for wide PAS angles.  As the PAS angle between microphones grows smaller, differences in suggested spacing also grow smaller.  At the limit with both microphones facing directly ahead (no angle between them) the spacing is the same regardless of pickup pattern.

In practical terms, the difference in suggested spacing for cardioids and for supercardioids is pretty minor.

Shotguns don't have smooth well-behaved polar patterns, and don't work very well as pairs in terms of stereo imaging.  Their pattern irregularities introduce complications which are more significant than these minor differences in spacing.  In general the same conceptual aspect applies though- if the PAS angle is narrow, space them more widely.  The values on the table are likely to be as good a starting point for a pair of shotguns as any.

I might use a shotgun from far back outside, but then I'd probably use just one of them pointing directly at the stage, placed in the center and mixed with a pair of widely spaced omnis.  The pattern irregularity would then be less of an issue and the imaging wouldn't be based solely on the angle/spacing relationship between a pair of shotguns.
Title: Re: PAS table (printable) - good imaging with high direct/reverberant pickup ratio
Post by: MIQ on August 18, 2014, 02:54:45 AM
Cardioid
Supercardioid
Hypercard patterns
Title: Re: PAS table (printable) - good imaging with high direct/reverberant pickup ratio
Post by: MIQ on August 18, 2014, 03:00:30 AM
80 deg angle
28cm spacing w each pattern
You lose about 5 degrees off each side if the Recording Angle going from Card to Super to Hyper
Title: Re: PAS table (printable) - good imaging with high direct/reverberant pickup ratio
Post by: MIQ on August 18, 2014, 03:09:47 AM
90 degrees
20cm spacing
Losing slightly larger amounts off each end of the Recording Angle as you move from Card to Super (9 deg)
and Super to Hyper (6 deg)
Title: Re: PAS table (printable) - good imaging with high direct/reverberant pickup ratio
Post by: MIQ on August 18, 2014, 03:24:22 AM
110 deg
17cm spacing
Losing similar amounts off each end of the Recording Angle as the DIN styles. Card to Super (9 deg) and Super to Hyper (7 deg).

Smaller angles between mics and bigger spacings lead to less difference between the different patterns. The Recording Angle becomes more dependent on time differences (mic spacing) and less on intensity differences (pattern shape) as the mic angle is reduced.

-Miq
Title: Re: PAS table (printable) - good imaging with high direct/reverberant pickup ratio
Post by: Gutbucket on August 18, 2014, 10:25:29 AM
For concert recording as done around here in situations where the taper chooses to use PAS, wide angles of 80 degrees or more are rare.  Angles narrower narrower than that will be far more common.
Title: Re: PAS table (printable) - good imaging with high direct/reverberant pickup ratio
Post by: MIQ on August 19, 2014, 03:15:38 AM
Sure, the further back in the room you get from the stacks, the less of an angle you'll need between the mics.  Like your table shows and you've discussed, the angle is getting small and the distance between mic is getting big. The Recording Angle becomes dominated by the arrival time difference and not the level differences caused by the mic patterns. 

Here's Card, Super, Hyper for 60deg mic angle and 50cm spacing
Title: Re: PAS table (printable) - good imaging with high direct/reverberant pickup ratio
Post by: MIQ on August 19, 2014, 03:18:10 AM
Here is 40 deg mic angle with 90cm spacing
Hardly any change in Rec Angle between them now.
Title: Re: PAS table (printable) - good imaging with high direct/reverberant pickup ratio
Post by: MIQ on August 19, 2014, 04:07:48 AM
How do you feel about the imaging you perceive when using configurations that rely mostly on arrival time differences (small angle with big spacings)?  To me the image created by widely separated mikes is spacious, but the individual positions of the performers is not well defined.  The other thing that keeps me from wanting to use narrow mic angles is that this often means you are too far back in the room. I realize that we don't always get to pick where we record, but if you get stuck too far back in the room, you get beyond the critical distance and there is not enough direct sound. Too much of the room usually just sounds bad to me. Who wants a recording from a bad seat at the show?

I think some of what has made DIN, NOS and ORTF style configs so popular is that they often work well from places in the room that sound good.  If the performers are spaced 80 to 100 degrees in front of you, you have a good chance at being in a spot that has a favorable direct to reverberant mix. Does that change substantially when the direct sound is coming mainly from the stacks? 

Another reason the semi-coincident configurations are popular is that they combine both arrival time and level differences to determine the image location.  This seems to provide a good compromise between a spacious sound and accurate image placement.

There are places where there is just no choice and you have to deal with a narrow recording angle, or a spot where you want to record with more directional mics to get less room and more direct sound, even when you are not beyond the critical distance. Applying the PAS table you provided or the Stereo Zoom concepts in general will give you a better chance at getting a recording you like.

Miq
Title: Re: PAS table (printable) - good imaging with high direct/reverberant pickup ratio
Post by: Gutbucket on August 19, 2014, 11:57:25 AM
The critical distance for most rooms is much closer than people generally think. Unless setup on stage, pretty much any recording position from out in the audience is going to be further than the critical distance.  That's certainly true at for unamplified music, a PA will have a somewhat different critical distance due to it controlled directionality, which extends the critical distance further into the room.  This improved PAS technique helps makes the best of normal taping positions which are pretty much always farther away than the critical distance.

The common problem with most PAS setups is not enough spacing between microphones, not too much.  That's due primarily to the limited size of commonly available mounting bars and the practical difficulties of spacing the microphones farther apart when doing so is appropriate, which is most of the time when recording from out in the audience due to the microphone PAS angles involved.  It's easy and common to use a standard narrow bar regardless of microphone angle.  Although it may also be less than ideal to use a wide bar with wide microphone angles, that error simply isn't very common or as much of a problem, certainly not in practical terms.

Some sound preferences are generally objective and agreed upon for most listeners, others will always be more personally subjective.  Much of the driving force behind this PAS stuff is objective as determined by listener testing (the Williams curves and those of other researchers), although within that personal subjective preferences appear in subtleties of degree at the margins.  On a personal level, I really dislike imaging which may be sharp if I hold my head perfectly still but is unstable and moves between the speakers when shift around on playback.  I find that trait more common with coincident setups, those that don't use sufficient spacing, and those which are overly monophonic.  That aspect doesn't bother some listeners as long as the imaging is sufficiently sharp.  It ruins the illusion for me.  I prefer a good balance of imaging, spaciousness, envelopment and ambience, with a stable soundstage.  I really like a good spaced omni recording or Decca tree (three omni) recording in a good room.  Personally I find the faults of wide, stable and immersive but fuzzy far less objectionable than flat, unstable, and overly dry, with pin-point sharp imaging.  It's much closer to what I hear and enjoy at a live performance and is more musically satisfying to me.  It’s the far less egregious error to my ear. 

Stereo is all an illusion.  There are always faults, but with the right knowledge at least the recordist can choose their own lesser poison.  These are just tools to help achieve the desired result, rather than a rules dictating what the results should be.
Title: Re: PAS table (printable) - good imaging with high direct/reverberant pickup ratio
Post by: carlbeck on August 19, 2014, 01:26:31 PM
My own recent experimentation has brought me in complete agreement with what was said above. For years I had been running the standard coincident & near coincident patterns, almost to a fault actually. Recently with my new microphones since they weren't actives, ie able to use in an active bar I've experimented with the PAS technique. I've been reading & re-reading the stereo zoom paper which makes a little more sense every time I read it before & after recording a show. For me the PAS technique has made better recordings, as a control factor I've still been running my actives on the same stand in Din or DINa which has been my usual configuration for the last decade. On every occasion I've preferred the PAS recording, it may be a matter of new microphones possibly but I try to focus on the imaging aspect, the feel of the room & overall listening pleasure. I've found the imaging to be just as good if not better with PAS, It's more than likely related to the rooms I record in but the point is that it is working for me. I don't find image quality to be less vs DIN which was my original fear plus I've had the added bonus of picking up more direct sound vs room reverb. Again, I think for what I do, recording rock & roll shows usually FOB within 50ft of the stage PAS is a better fit, if I ever run on stage then I will revert back to DIN, DINa or ORTF but I rarely record on stage. As with everything it's a personal preference, if it works for you & you're pleased with your recordings then it's a win-win in my book.
Title: Re: PAS table (printable) - good imaging with high direct/reverberant pickup ratio
Post by: MIQ on August 20, 2014, 05:07:25 AM
Thanks for the great replies.  :)

The critical distance for most rooms is much closer than people generally think. Unless setup on stage, pretty much any recording position from out in the audience is going to be further than the critical distance.  That's certainly true at for unamplified music, a PA will have a somewhat different critical distance due to it controlled directionality, which extends the critical distance further into the room.  This improved PAS technique helps makes the best of normal taping positions which are pretty much always farther away than the critical distance.

I probably should have written "well beyond the critical distance".

Carlbeck, in your recent experiments do you recall the recording/PAS angles you used?  Were they less than 60 deg? 

I like and think I understand the advantages of capturing as much of the direct PA sound using directional mics pointed on axis at the stacks.  I'm still wondering what the venues are like that have really narrow recording/PAS angles but still have a nice direct to room sound at the mics. The rooms I've taped in aren't huge and have a square or rectangular floor plan with the stage along the long side of the rectangle.  I'm usually able to get fairly close to the stage with my mics. I guess I could imagine and think I have seen a few pics here of narrow rooms that might require narrow mic angles and still have a good balance of direct and room sound.  The times I've had to record more narrow recording angles have been from places in the room that had too much room sound and I have not liked the recordings.

For people applying the PAS technique or the Stereo Zoom techniques in general, what kind of recording/PAS angles are you using?  What are they for the recordings you think sound the best?  What is the range of "normal" recording angles for the kind of taping most people are doing around here? 

Miq
Title: Re: PAS table (printable) - good imaging with high direct/reverberant pickup ratio
Post by: Gutbucket on August 20, 2014, 09:59:05 AM
The times I've had to record more narrow recording angles have been from places in the room that had too much room sound and I have not liked the recordings.

Making the best of those kinds of less than ideal situations is the primary goal of this technique.  That and simplifying setup.

At the critical distance in a good sounding room, a pair of omnis are likely to get a good balance of direct and reverberant sound. From far away, pointing directional mics directly at the source makes the most of the direct sound reaches that position.

When recording closer to the critical distance in good sounding environments, the Stereo Zoom concept on which this technique is based still applies, but it becomes less and less necessary to point highly directional microphones right at the PA to maximize the pickup of whatever direct sound is available reaching the recording position.  So alternate Stereo Zoom solutions may be prefered which provide different flavors of imaging, different perceptions of depth, and different balances of room sound and distribution of that reverberation in the playback image.  At some point when moving closer (remaining on-axis to the PA, not moving into the "too close, off-axis dead zone" of the PA, which is a different issue), the sound will get overly dry using this technique and choosing another setup which doesn't emphasize the direct PA sound maximally will be a better choice.  But that's far less common for most tapers than being in a less than great sounding room and/or recording from farther back.
Title: Re: PAS table (printable) - good imaging with high direct/reverberant pickup ratio
Post by: carlbeck on August 20, 2014, 11:44:56 AM
Thanks for the great replies.  :)

The critical distance for most rooms is much closer than people generally think. Unless setup on stage, pretty much any recording position from out in the audience is going to be further than the critical distance.  That's certainly true at for unamplified music, a PA will have a somewhat different critical distance due to it controlled directionality, which extends the critical distance further into the room.  This improved PAS technique helps makes the best of normal taping positions which are pretty much always farther away than the critical distance.

I probably should have written "well beyond the critical distance".

Carlbeck, in your recent experiments do you recall the recording/PAS angles you used?  Were they less than 60 deg? 

For people applying the PAS technique or the Stereo Zoom techniques in general, what kind of recording/PAS angles are you using?  What are they for the recordings you think sound the best?  What is the range of "normal" recording angles for the kind of taping most people are doing around here? 

Miq

I've been between 60 & 70 degrees on average, it's not that different than a standard DIN in most cases but I've been focusing on achieving better distance between the capsules. Quite frankly unless you're an imaging nut like I am most wouldn't tell the difference. The benefit has been easier set up (for me at the time of the show) with a noticeable improvement in direct sound. Last night I taped in a small bar setting & we had the opportunity to clamp on a beam that was two feet from the stacks (speakers actually) so I ran DIN, it made sense being on top of the sound source & less than three feet off the stage. Imaging is of course superb but I attribute that more to the location of soundsource than standard configs.
Title: Re: PAS table (printable) - good imaging with high direct/reverberant pickup ratio
Post by: MIQ on August 22, 2014, 03:05:46 AM
Gut, nice explanation of the application of different mic techniques to different recording locations, and the transition from wanting to capture as much direct PA sound as possible to applying the Stereo Zoom concepts to optimize for, or flavor with, other recording attributes.
 
Quite frankly unless you're an imaging nut like I am most wouldn't tell the difference.

I'm definitely an imaging nut too.    ;D

Thanks
Title: Re: PAS table (printable) - good imaging with high direct/reverberant pickup ratio
Post by: Gutbucket on March 30, 2016, 05:43:03 PM
Try figure 8's in PAS outdoors.  They require the least spacing between mics of any pattern.  See here- http://taperssection.com/index.php?topic=177050.0
Title: Re: Improved PAS setups - better imaging with higher direct-sound/reverberant ratio
Post by: Gutbucket on August 04, 2017, 03:01:47 PM
Interesting streaming listening comparison of a few different microphone setups allowing one to listen to the way they capture stereo ambience at Helmut Wittek's Hauptmikrofon website, here- http://www.hauptmikrofon.de/audio/stereoambience.html

Granted none of the samples are of music, but they do provide a useful basic comparison for hearing the differences between X/Y coincident, two near-spaced setups (ORTF and improved-PAS-like), and a spaced omni configuration.

I'm posting the link here because I find I personally prefer the setup labeled "quasi-ORTF" for all samples there except the construction site, and that "quasi-ORTF" setup closely resembles a typical "Improved-PAS" configuration (40cm / 40 degrees) with the microphones angled only 20 degrees away from center - which is a pretty typical PAS angle from the taper section or soundboard area further back in the room.  Only on the construction site sample did I prefer the ORTF sample for it's more distinct left/right imaging width.  For all the other samples I felt the quasi-ORTF samples produced a better balance between sharp imaging (X/Y furthest to that extreme) and natural sounding diffuse ambient openness (spaced omnis furthest to that extreme).


A few comments-

I was listening on headphones.

There is no right or wrong choice here, only personal preference.

I like the improved-PAS-like quasi-ORTF samples here because of their stereo qualities - that is to say, how they reproduce the sound, even though it is not actually being leveraged for the reasons we'd choose PAS!  It just sounds better to me than the other samples.  Where as the primary purpose for choosing PAS is to either simplify setup, or maximize the direct/reverberant ratio as much as possible.  It's very encouraging that it also simply sounds better and more natural to me when in a prefered recording location without the ease of setup constraint.

I like to angle spaced omnis apart from each other rather than pointing parallel to each other, especially if that pair is the only mics I'm using.  That provides some additional level difference information at high frequencies which makes the imaging somewhat less washy and more distinct.  I think that would improve the spaced omni samples here, but the way its been done here more clearly represents the basic differences between setups without that kind of modification.

I wish there was a way to play both the spaced omnis and X/Y samples simultaneously.  I like that setup for live music recording because it sort of gets the best of both worlds.  There was a sample player page at the Schoeps website at one point (may still be up) which allowed similar samples to be played singly or simultaneously.   I don't think it was intended for simultaneous playback of more than one sample at a time but it worked.  It was very interesting hearing the difference between each setup on its own as well as combinations of two setups, as in a four microphone configuration.  It helped confirm my suspected preference for X/Y + spaced omnis over near-spaced + spaced omnis, and over all of the two mic configurations alone.  Best of both worlds from a harmonious combination.
Title: Re: Improved PAS setups - better imaging with higher direct-sound/reverberant ratio
Post by: heathen on August 04, 2017, 03:17:50 PM
Do you know what they mean by "open cardioids" in the quasi-ORTF examples?  I'm assuming it's a wide cardioid or the like.  I'd be curious why they didn't use a the same cardioids for the quasi-ORTF as they used for XY and ORTF.
Title: Re: Improved PAS setups - better imaging with higher direct-sound/reverberant ratio
Post by: Gutbucket on August 04, 2017, 03:34:19 PM
Good catch, I didn't see that.  That would be the Schoeps mk22, which is between a cardioid (mk4) and subcardioid (mk21) in pattern.  I didn't realize they'd used different capsules for the ORTF and modified-ORTF samples.  That does complicate things and make the comparison a bit less useful for our purposes by introducing another variable.  I generally like the sound of the mk22 better, as long as it works in the acoustic and assuming all else is equal except the setup configuration, so I now need to take that into consideration in my preference for modified-ORTF in these samples.
Title: Re: PAS table (printable) - good imaging with high direct/reverberant pickup ratio
Post by: morst on August 05, 2017, 07:00:13 PM

Quite frankly unless you're an imaging nut like I am most wouldn't tell the difference.

I'm definitely an imaging nut too.    ;D
Not me. I go for even channel balance. Don't really even consider imaging in post. And my mic placement is pretty much point & shoot. I used to use cards in ORTF exclusively, until I lost the mounting bar, now I run X/Y, and place them where it might sound the best and not be a hassle to maintain the spot.

The stereo zoom info has only just crept into my thinking. Maybe it will affect my setups and mixes, maybe not...  ???
Title: Re: Improved PAS setups - better imaging with higher direct-sound/reverberant ratio
Post by: noahbickart on August 06, 2017, 05:51:26 PM
Good catch, I didn't see that.  That would be the Schoeps mk22, which is between a cardioid (mk4) and subcardioid (mk21) in pattern.  I didn't realize they'd used different capsules for the ORTF and modified-ORTF samples.  That does complicate things and make the comparison a bit less useful for our purposes by introducing another variable.  I generally like the sound of the mk22 better, as long as it works in the acoustic and assuming all else is equal except the setup configuration, so I now need to take that into consideration in my preference for modified-ORTF in these samples.

To my ears and to my playback transducers, the mk22 is the finest capsule Schoeps makes and can be used in the widest possible scenarios.

I *always* run a pair of mk22 no matter what.
Title: Re: Improved PAS setups - better imaging with higher direct-sound/reverberant ratio
Post by: morst on August 06, 2017, 07:41:55 PM
I *always* run a pair of mk22 no matter what.

Do you have a standard way of positioning them? I just got a pair of Neumann KM143's, their Wide Cardioid condensers, and have only used them a few times, and all but once, on stage. Very interested in practical experience with the Hypocardioid (!) pattern!!
Title: Re: Improved PAS setups - better imaging with higher direct-sound/reverberant ratio
Post by: noahbickart on August 11, 2017, 02:27:16 PM
I *always* run a pair of mk22 no matter what.

Do you have a standard way of positioning them? I just got a pair of Neumann KM143's, their Wide Cardioid condensers, and have only used them a few times, and all but once, on stage. Very interested in practical experience with the Hypocardioid (!) pattern!!

I try to use the PAS theory with them. I've found that a 35cm spread at 70 degrees tends to work well from the OTS at MSG. FOB, I've used them with a NOS setup with good results. Onstage I've used them at 21cm and 110 degrees.

Basically apply the stereophonic zoom, knowing that you'll always want a little wider spacing than regular cardioids.
Title: Re: Improved PAS setups - better imaging with higher direct-sound/reverberant ratio
Post by: Gutbucket on May 24, 2018, 06:51:47 PM
^ And that's what this Improved PAS technique does.  It makes the application of Stereo Zoom to Point At Stacks simple.

I'm posting to notify thread readers of an edit I just made correcting a minor copy/paste typo in the extended table GIF and PDF in the initial post.  Previously the SRA numbers for the 50 degree PAS angle column were off by 10 degrees, copied from the cell immediately above without modification.  Nothing major, the edit doesn't effect the recommended spacing numbers and that column is mostly just informational, but has now been corrected.  Typo was pointed out to me by a TS member earlier today (thanks man).