Become a Site Supporter and Never see Ads again!

Author Topic: Relationships between spaced omnis and center mic  (Read 1547 times)

0 Members and 1 Guest are viewing this topic.

Offline heathen

  • Trade Count: (5)
  • Taperssection Member
  • ***
  • Posts: 279
Relationships between spaced omnis and center mic
« on: June 18, 2017, 05:02:35 PM »
I've read several old threads on here about spaced omnis, with some discussions as well about running a mic (or pair) in the center.  The threads have been very interesting, though sadly I'm unable to keep up with the more technical discussions.

My question concerns the relationship between the omnis and the center mic.  I gather that they should all be on the same horizontal plane (right?), and that it's generally okay for the center mic (in my case a cardioid) to be further forward than the omnis.  There must be a point where the center mic is too far forward, though, right?  How far is too far, though, and does it depend on the distance the omnis are spread? 
Mics: Core Sound TetraMic | Countryman B3 | CA-14 omnis | AT853 cards | AKG 460/ck61 | Studio Projects CS5
Decks: Zoom F4 | Tascam DR-70D | Roland R-05

Offline Gutbucket

  • record > listen > revise technique
  • Trade Count: (13)
  • Needs to get out more...
  • *****
  • Posts: 11361
  • Gender: Male
Re: Relationships between spaced omnis and center mic
« Reply #1 on: June 19, 2017, 07:17:20 PM »
Yes to most of your questions.  You're on the right track in your thinking.  The answer ranges between all mics in a single horizontal line, to the center mic being moved well forward of the omnis (with compensating delay applied to it).  Usually having the center just slightly but not overly far out in front (without any compensating delay) works well for both practical and acoustical reasons, which I'll try to outline in more detail later.

The good news is there is a lot of leeway without screwing things up.  Much more than there is with simple 2-channel stereo configurations.


Edit-
After posting a bunch of stuff explaining why later in the thread, here's a short synopses of my practical take away- 

For section recording using only a pair of omnis alone, I want an spacing of about 3'.  Less isn't as good in terms of imaging, ambiance, bass, and openness.  More spacing might work but risks a hole-in-the middle. 

If using a center mic I want an omnis spacing of 3' or more.  Less isn't as good in terms of imaging, ambiance, bass, and openness, and risks imaging and comb-filtering complications more than just a pair of omnis alone.  It could be advantageous for other reasons though.  More spacing between omnis can be beneficial and is less problematic because the center mic fills the hole in the middle, but I still wouldn't go crazy wide or the center is becomes separate and "spotlighted".

If the omnis can't be spaced far enough apart, it can help to move the center mic well far forward (like 6' or so) and delay it to compensate for that distance, but that's not often practical.  Alternatively one could move the center mic it straight up or straight down, without requiring any delay, but that might not be very practical either.  Either approach gets the three mics far enough apart to minimize problems of having them too close to each other.  You don't want the three mics too close together.

By using a coincident center pair in the center instead of a single mic, I optimize things and get the best of envelopment and imaging at the same time.  Like a single center mic, I ideally want an omni spacing of 3' or more for the same reasons.  Yet because I can then adjust the image width of the center coincident pair, even wider spacings between omnis no longer present a problem.  I can go double-wide or even more with the omnis without potential problems, giving me a wide diffuse ambience which stays out of the way of the sharp directional imaging stuff in the center provided by the coincident pair.  I also gain control over image blend between the center and sides of the playback image by varying the width from the coincident stereo pair afterwards.
« Last Edit: June 23, 2017, 07:18:03 PM by Gutbucket »
volition > vibrations > voltages > numeric values | numeric values > voltages > vibrations > virtual teleportation time-machine experience

Offline heathen

  • Trade Count: (5)
  • Taperssection Member
  • ***
  • Posts: 279
Re: Relationships between spaced omnis and center mic
« Reply #2 on: June 20, 2017, 10:37:05 AM »
The answer ranges between all mics in a single horizontal line, to the center mic being moved well forward of the omnis (with compensating delay applied to it)

How do I figure out how much compensating delay to apply to the center mic? 
Mics: Core Sound TetraMic | Countryman B3 | CA-14 omnis | AT853 cards | AKG 460/ck61 | Studio Projects CS5
Decks: Zoom F4 | Tascam DR-70D | Roland R-05

Offline rocksuitcase

  • Trade Count: (0)
  • Needs to get out more...
  • *****
  • Posts: 3913
  • Gender: Male
    • RockSuitcase: stage photography
Re: Relationships between spaced omnis and center mic
« Reply #3 on: June 20, 2017, 11:01:41 AM »
Heath,
in our experience the center mic can be 3-6 inches forward of the omnis with no delay needed. We haven't done a config where the centers are more than that so I can't answer the how far is far enough to require delay. Lee can answer that I'm sure.
edited to add two photos for you-
First one is set up at home with three mics, you can see the center is about 3-4 inches ahead of the sides. (it is also a 1-2 inches out of axis in the horizontal plane, which we've tried to have the correct adapters to eliminate that distance- that said, I do not think it has affected the sound quality)
Second is our set up at DeadnCo 2016. (pink dead rats not our rig!)
« Last Edit: June 20, 2017, 11:11:41 AM by rocksuitcase »
music IS love

When you get confused, listen to the music play!

Mics:         AKG460|CK61|CK1|CK3|CK8|Beyer M 201E
Recorders:Marantz PMD661 OADE Concert mod; Tascam DR680 MKI

Offline heathen

  • Trade Count: (5)
  • Taperssection Member
  • ***
  • Posts: 279
Re: Relationships between spaced omnis and center mic
« Reply #4 on: June 20, 2017, 11:27:52 AM »
That's a cool setup rocksuitcase.  What are the outer mics?  Looks like maybe AKG bodies, but capsules that are at a right angle?  Pardon my ignorance.

I'd be curious to hear a sample of one of your recordings...are there any on LMA?
Mics: Core Sound TetraMic | Countryman B3 | CA-14 omnis | AT853 cards | AKG 460/ck61 | Studio Projects CS5
Decks: Zoom F4 | Tascam DR-70D | Roland R-05

Offline rocksuitcase

  • Trade Count: (0)
  • Needs to get out more...
  • *****
  • Posts: 3913
  • Gender: Male
    • RockSuitcase: stage photography
Re: Relationships between spaced omnis and center mic
« Reply #5 on: June 20, 2017, 11:49:26 AM »
That's a cool setup rocksuitcase.  What are the outer mics?  Looks like maybe AKG bodies, but capsules that are at a right angle?  Pardon my ignorance.

I'd be curious to hear a sample of one of your recordings...are there any on LMA?
Outside are AKG c460 bodies with ck22 Omni caps (the flattest Omni AKG made) the angles are the A-60 "knuckle" adapters which offer the swivel angling. We use the swivel to gain about 10 cm on the outside spread.
The center in that pic is an old Beyer M201e, but we typically run AKG ck61 actives in center/rear.
Here is one:
https://archive.org/details/steepcanyon2016-07-14.24.ck22ck414.flac               (this one has AKG 414 cards in the center)

One more:
https://archive.org/details/erevival2016-07-16.ck22ck61
We ran the centers with both AKGck61 and AKGck8 facing fwd. In mixdown, I chose the ck61 only. But it is nice to have options. (photo is of the two fwd facing mics in this config)


« Last Edit: June 20, 2017, 01:12:59 PM by rocksuitcase »
music IS love

When you get confused, listen to the music play!

Mics:         AKG460|CK61|CK1|CK3|CK8|Beyer M 201E
Recorders:Marantz PMD661 OADE Concert mod; Tascam DR680 MKI

Offline heathen

  • Trade Count: (5)
  • Taperssection Member
  • ***
  • Posts: 279
Re: Relationships between spaced omnis and center mic
« Reply #6 on: June 21, 2017, 12:21:57 AM »
Here's a sample of a recording I made with my current setup over the weekend, I'd appreciate any feedback (especially as to whether there are any sonic issues from the center being relatively far forward from the sides...I didn't apply any delay in post): https://we.tl/HH4AeXxm70 (WeTransfer download link).

Details...

Source: Church Audio CA 14 omnis spaced ~9 inches, Church Audio Ugly Battery Box; AKG 460/ck61 (center, about 8 inches forward of the omnis); Tascam DR-70D (24/96 wav)

Location: Stand ~7 feet high, ~5 feet right of center, next to sound/light booth

The crowd was pretty loud and talkative, so you may want to skip to the middle of the track.  Also, there was a wall not far to my right, but it was relatively open all to the left (I didn't have a lot of say in where I was able to put up my stand).  I only had the omnis spread ~9 inches because if I went further that would put the right side that much closer to the wall, and potentially in the light guy's face.

In post I panned the omnis hard left and right, and gave them a tiny bit of gain.  I gave the left side 1 dB of gain more than the right because of the wall issue.
Mics: Core Sound TetraMic | Countryman B3 | CA-14 omnis | AT853 cards | AKG 460/ck61 | Studio Projects CS5
Decks: Zoom F4 | Tascam DR-70D | Roland R-05

Offline noahbickart

  • Site Supporter
  • Trade Count: (25)
  • Taperssection All-Star
  • *
  • Posts: 1515
  • Gender: Male
  • Nobody's finished, we ain't even begun
Re: Relationships between spaced omnis and center mic
« Reply #7 on: June 21, 2017, 01:20:32 PM »
The answer ranges between all mics in a single horizontal line, to the center mic being moved well forward of the omnis (with compensating delay applied to it)

How do I figure out how much compensating delay to apply to the center mic?

Speed of sound is ~1120 feet per second depending on altitude and temperature. So measure the distance....

There's an online calculator here: http://www.doctorproaudio.com/doctor/calculadores_en.htm

Follow links for an iOS app as well.
« Last Edit: June 21, 2017, 01:29:15 PM by noahbickart »
Recording:
Capsules: Schoeps mk41v, mk4v, mk22, mk3 & mk8
Cables: 2x nbob KCY, 1 pair nbob actives, Darktrain 2 and 4 channel KCY extensions:
Preamps:    Naiant Littlebox, Naiant IPA, Naiant PFA, Sound Devices Mixpre6
Recorders: Sound Devices Mixpre6, Sony PCM m10
Home Playback: Mytek Stereo96> Adcom SLC 505> Marantz Ma500 (x2)> Eminent Tech LFT-16; Musical Fidelity xCan v2> Hifiman HE-400
Office Playback: Grace m903> AKG k701

Offline rocksuitcase

  • Trade Count: (0)
  • Needs to get out more...
  • *****
  • Posts: 3913
  • Gender: Male
    • RockSuitcase: stage photography
Re: Relationships between spaced omnis and center mic
« Reply #8 on: June 21, 2017, 01:29:24 PM »
Here's a sample of a recording I made with my current setup over the weekend, I'd appreciate any feedback (especially as to whether there are any sonic issues from the center being relatively far forward from the sides...I didn't apply any delay in post): https://we.tl/HH4AeXxm70 (WeTransfer download link).

Details...

Source: Church Audio CA 14 omnis spaced ~9 inches, Church Audio Ugly Battery Box; AKG 460/ck61 (center, about 8 inches forward of the omnis); Tascam DR-70D (24/96 wav)

Location: Stand ~7 feet high, ~5 feet right of center, next to sound/light booth

The crowd was pretty loud and talkative, so you may want to skip to the middle of the track.  Also, there was a wall not far to my right, but it was relatively open all to the left (I didn't have a lot of say in where I was able to put up my stand).  I only had the omnis spread ~9 inches because if I went further that would put the right side that much closer to the wall, and potentially in the light guy's face.

In post I panned the omnis hard left and right, and gave them a tiny bit of gain.  I gave the left side 1 dB of gain more than the right because of the wall issue.
Heath, that link goes to a file titled A Live One 20140617 Theme from the Bottom        10:05 tracktime. is it possible this is not the file you intended to post for us?
music IS love

When you get confused, listen to the music play!

Mics:         AKG460|CK61|CK1|CK3|CK8|Beyer M 201E
Recorders:Marantz PMD661 OADE Concert mod; Tascam DR680 MKI

Offline heathen

  • Trade Count: (5)
  • Taperssection Member
  • ***
  • Posts: 279
Re: Relationships between spaced omnis and center mic
« Reply #9 on: June 21, 2017, 01:32:16 PM »
Heath, that link goes to a file titled A Live One 20140617 Theme from the Bottom        10:05 tracktime. is it possible this is not the file you intended to post for us?

No, that's the one I intended to post.  Why?
Mics: Core Sound TetraMic | Countryman B3 | CA-14 omnis | AT853 cards | AKG 460/ck61 | Studio Projects CS5
Decks: Zoom F4 | Tascam DR-70D | Roland R-05

Offline heathen

  • Trade Count: (5)
  • Taperssection Member
  • ***
  • Posts: 279
Re: Relationships between spaced omnis and center mic
« Reply #10 on: June 21, 2017, 01:35:38 PM »
Speed of sound is ~1120 feet per second depending on altitude and temperature. So measure the distance....

There's an online calculator here: http://www.doctorproaudio.com/doctor/calculadores_en.htm
So we're talking significantly less than a hundredth of a second...is that even going to be perceptible to human ears?
Mics: Core Sound TetraMic | Countryman B3 | CA-14 omnis | AT853 cards | AKG 460/ck61 | Studio Projects CS5
Decks: Zoom F4 | Tascam DR-70D | Roland R-05

Offline rocksuitcase

  • Trade Count: (0)
  • Needs to get out more...
  • *****
  • Posts: 3913
  • Gender: Male
    • RockSuitcase: stage photography
Re: Relationships between spaced omnis and center mic
« Reply #11 on: June 21, 2017, 01:37:13 PM »
Heath, that link goes to a file titled A Live One 20140617 Theme from the Bottom        10:05 tracktime. is it possible this is not the file you intended to post for us?

No, that's the one I intended to post.  Why?
because you said: a recording I made with my current setup over the weekend
and this sample is titled : A Live One 20140617         which appears to be from 2014.
If it is the sample you want us to listen to, I have heard it once and can say I do not hear any center channel timing issues.
music IS love

When you get confused, listen to the music play!

Mics:         AKG460|CK61|CK1|CK3|CK8|Beyer M 201E
Recorders:Marantz PMD661 OADE Concert mod; Tascam DR680 MKI

Offline heathen

  • Trade Count: (5)
  • Taperssection Member
  • ***
  • Posts: 279
Re: Relationships between spaced omnis and center mic
« Reply #12 on: June 21, 2017, 01:38:23 PM »
Whoops that's just a typing error on my part in the file name.  Sorry about that, and thanks for giving it a listen!
Mics: Core Sound TetraMic | Countryman B3 | CA-14 omnis | AT853 cards | AKG 460/ck61 | Studio Projects CS5
Decks: Zoom F4 | Tascam DR-70D | Roland R-05

Offline F.O.Bean

  • Is a 4 channel slut and
  • Trade Count: (121)
  • Needs to get out more...
  • *****
  • Posts: 40568
  • Gender: Male
  • Taperus Maximus
Re: Relationships between spaced omnis and center mic
« Reply #13 on: June 21, 2017, 03:32:36 PM »
I think it sounds good too! I don't hear any kind of delay and overall it sounds really good, minus the chatter! That's why I LOVE running my mk41 supercards when they Chatty Cathy's are out ;D
Schoeps MK4's | MK41's ->
Schoeps | NBob 250/05 KCY's ->
Schoeps VMS 02IB | Naiant +60v/Low Noise PFA's ->
DarkTrain Right Angle Stubby | GakCable XLR's ->
Sound Devices MixPre-6 | Tascam DR-70D ->
128gb | 64gb SanDisk Extreme Pro SDXC-I

http://www.archive.org/bookmarks/diskobean | http://www.archive.org/bookmarks/Bean420 | http://bt.etree.org/mytorrents.php

Offline Gutbucket

  • record > listen > revise technique
  • Trade Count: (13)
  • Needs to get out more...
  • *****
  • Posts: 11361
  • Gender: Male
Re: Relationships between spaced omnis and center mic
« Reply #14 on: June 22, 2017, 03:27:35 PM »
First, at the risk of a collective ::), allow me a quick philosophical muse on the approach to recording in order to better ground my contribution to the discussion.   I'll then get into specifics on technique.  Partly because all this is related, and partly because I think it helps in determining where to best focus one's efforts before getting mired in the details. It's easy to get swept up in specifics and loose the big-picture focus on what's actually important, especially when discussing alternative approaches to the norm.  So please forgive a brief full forest view before closer examination of tree bark.

There is a whole lot of stuff going on with stereo recording and reproduction.  Stereo is an illusion, a mental trick in which we willingly play a part as listeners.  Creating a convincing illusion is not a simple direct application of one optimal working method, but rather a juggling of multiple phenomena to produce an illusion which is sufficiently convincing for the listener.  That is to say there is no one correct way of doing things.  In that light, the art of recording concerns juggling various phenomena in pursuit of a more convening illusion.  Some of the phenomena involved are intuitive and others are not, and some are contradictory with each other.  In the end whatever works to make the illusion more believable for the listener is what makes an approach correct or not.  Realistically, we're usually leveraging a combination of approaches, juggling benefits and trade-offs.

Below is a list of aspects we have control over as recordists, ranked in order of what I feel is most important.  Others may disagree on the the order of this list, but I have good arguments for ranking it this way.  The most critical, fundamental stuff is at the top, the higher-order nice-to-have stuff at the bottom.  There are of course other more important and less important things, above all else the quality of the performance at the very start of the chain and a willing suspension of disbelief on the part of the listener at the very end of the chain, both of which are outside our sphere of influence-

signal integrity (sufficient elimination of noise, overload, clipping, dropouts and other problems)
frequency balance
direct/reverberant energy balance (intelligibility, sense of proximity)
loudness dynamics
sense of space (width and depth)
directional imaging
sense of envelopment and immersion


Ideally I want all those things optimized, but that's a lot to ask.  It's also not necessary.  Fortunately we can lean on our willing suspension of disbelief and enjoy less than perfect recordings that don't satisfy all those aspects.  The point I'm trying to make is this- when the stuff closer to the top of that list isn't quite right, it really impedes our listening enjoyment.  When the stuff closer to the bottom of the list isn't quite right (or isn't present at all), it doesn't matter as much. The higher-order aspects at the bottom of the list (which is the stuff we tend to get excited about in good recordings) really only become valuable when they are supported by a strong foundation consisting of stuff at the top working well.  The higher-order bottom of the list stuff doesn't have a good change at becoming convincing unless the lower order stuff has been rendered sufficiently transparent such that the listener is no longer consciously aware of them.
« Last Edit: June 22, 2017, 04:08:27 PM by Gutbucket »
volition > vibrations > voltages > numeric values | numeric values > voltages > vibrations > virtual teleportation time-machine experience

 

RSS | Mobile
Page created in 0.249 seconds with 37 queries.
© 2002-2017 Taperssection.com
Powered by SMF
Website Design by Foxtrot Media, Inc., a Baltimore Website Company