Topic: 4 channels?

[Brian Skalinder]

For the original poster:  it's difficult to advise how to achieve a "fuller sound" without samples of recordings with which you're dissatisfied, details about the environments in and types of music which you record, and more information about how you use the C4s (e.g. which caps, in what configurations, location and height relative to sound source, etc.).  Without those details, the thread will continue to be interesting with respect to multiple mic channels, but not particularly helpful relative to your specific needs.

[Gutbucket]

The bulk of my experience with the J-disk comes from another Springfest 5 years ago or so at the same venue mentioned above, using a normal sized disk- varying both the mic spacing and fore/back position on the disk a lot during a couple sacrifical test sets, and leaving it set in a few different positions for the non-sacrificial ones. That was recording from the audience FOB at about the apex of an equalateral triangle with the PA stacks. I heard the increased seperation you mention with the mics close, which at some point began to shadow the center, maybe more in timbre than level.  I remember thinking a lot about how far around the front of the disk each mic could 'see' and how much overlap there was.  With the mics really close, the overall timbre and the center of the image particularly seemed to have the high frequencies rolled off significantly which I didn't care much for, but what bothered me more than that was the lack of the open and wide feel I could only get with more spacing, and that's what got me thinking about a big enough disk to be able to space the mics somewhat more, while trying to keep the same angle around the front that the mics could 'see', which made the disk get large fast. 

I prefered the J-disk onstage, but only did that a few times as I moved on to multiple spaced omnis for that which were less visually intrusive and I liked how 3 or 4 spaced omnis were more likely to place at least one mic closer to each performer or whatever was going on when I was recording at stage-lip.  From farther back, spacing the mics more without the disk worked better for me and was easier.  The two disk idea morphed into the much more practical experiments with mounting the miniature omnis in small diameter balls to make them a bit more directional in the high frequencies so I didn't have to space them as much.  I still do that at that same venue for Bear Creek in the fall, where I'm runing way up front at the stage-lip or railing and need to keep the 4-way decca tree smaller and more managable so I limit it to a 3' L/R spacing or less and use the balls on all 4 mics. 

Apologies to the original poster for pretty much comandeering the thread.

[notlance]

I have not seen this mentioned on this thread, (maybe I missed it) but a good use of 3 channels is a Double M/S configuration.  A DMS rig adds a rear facing cardioid to the standard “Mid cardioid /Side figure-8” M/S configuration.  Adding this rear facing cardioid does two things:

1. Allows you to have any front facing (and rear facing too if you want) virtual microphone pair of any pattern at any mic angle, and you can do it in post production.  If, for example, you want to hear what a Blumlein pair sounds like you can do it after you have made the recording.

2. Allows you to easily derive 5 surround channels from three microphones.

This paper describes the M/S technique, but it illustrates how by varying the middle mic pickup pattern and the Mid Side balance you can have any virtual mic pair at any angle.

http://www.wesdooley.com/pdf/technique.pdf

By using a Mid “twin” mic such as a Sennheiser MKH800 Twin or a Neavton MC404 plus a Side figure-8 you can set up a DMS rig with only two mic bodies.  I have used DMS as my standard mic configuration for several years now due to its flexibility and low profile.

So what to do with the 4th channel?  Often I'll use it as a spot mic for soloists or for vocals.

[Gutbucket]

DMS is a great maximization of possibilities from three channels.  However, like four channel ambisonic systems (which are basically similar but also capture height info) it’s limited to coincident mic techniques only.  The setups available with DMS and ambisionic mic are excellent representations of any coincident technique which can be tweaked to perfection after the fact (which really is the most amazing part), but if means giving up any spacing/time-information in your recordings if that is something you like. 

Because it’s always coincident, basic decoding for up to 4 horizontal channels works well, but 5 or more channel surround is somewhat compromised in theory (multiple first order virtual mic patterns begin to overlap too much).  I have an Tetramic ambisonic system but have only used it to output two channels at this point so I can't confirm that from experience.  More advanced decoding techniques which I don't understand are becoming available though, which may make that less of an issue in the future.  AFAIK that is not available yet in the Schoeps DMS plugin.

notlance, have your used DMS to derive 5 channel surround? If so, what was your real world impression?

[Gutbucket]

I've just recently come across the Optimum Cardioid Triangle technique.  I've been thinking I might want to try that out, though it violates my policy of not arranging my mics to keep a 2ch "out" that I can always fall back on.
[snip]

Gut -- what was your experience with OCT?

Didn't want to forget you Todd before I shut up.

In its original form OCT was designed around 3 channel L/C/R playback and surround recording if additional channels are recorded, but not 2 channel stereo.  The interesting thing about OCT is that it is designed to minimize unwanted crosstalk between the front three channels by using both the directivity of the mics and the spacing between them.  In that sense it was optimized specifically for three channel L/C/R recording without any concern for 2 channel compatibility.

There is a newer revised version called OCT2 which is supposedly adapts the original setup for 2 channel compatibility.  OCT2 moves the center mic farther forward and adds a short delay to it to compensate.  I think the idea there is the whole multiple near-spaced mics correlation thing again.  If I understand what’s going on with correctly with the OCT2 changes, moving the center mic physically forward decorellates it from the side facing pair enough (decorellates the diffuse field sound) to allow the three channels to be mixed to two without problems, while the delay brings the direct sound arriving from the forward direction back into the same timing relationship as OCT.  Head spin that one.  So if 2 channel output is the goal, then OCT2 is theoretically the one you’d want.  I’m not sure the difference is significant or not for what we do.

I’ve run OCT/OCT2 a couple times on-stage as an experimental thing when I already had a standard setup going and could just throw the side facing supercards up too.  The array dimensions were accurate, but the setup was a bit bastardized.  I used 24” spaced ADK TL’s in supercardioid as L/R and had two different mics I could use as the center which were already setup in my alternate rigs- one was a Tetramic at about the OCT center placement, only vertically higher (which probably decorellated it as much as moving it forward).  I could decode that to a forward facing cardioid. The other was a 4060 omni boundary mounted on the stage surface farther forward at about OCT2 center placement. I listened in three channel (and surround using two other room mics) to get a feel for what it could do and really liked the separation and angular precision of the forward image.  I never bothered mixing the three channels down to two or applying the OCT2 delay for those listening tests.  My feeling was that the setup is great if ultimate imaging accuracy in three channel playback is the goal, and can see that it may work well for two channels as well (given the added complexity of adding the delay, if it’s even needed).  I also listened to just the spaced side facing supercards alone in two channel to see what they sounded like, and was surprised that it wasn’t nearly as bad as I figured it would be- wide and side sensitive, and mostly more diffuse and less direct for onstage sound.

In the end I decided to use other techniques for that on-going gig because precise angular imaging was NOT what was most important for me in that scenario.  The gig is a jazz trio with upright bass on one side of the drum kit and electric guitar on the other.  The stage volume and projection of the guitar amp can overwhelm the delicate jazz drum work and the bass if recording from a perfectly centered stage location, so I usually setup directly in front of the bass on the snare side of the kit and arrange the mics to look across the kit towards the more distant guitar to balances things in both level and in image.  I can’t easily physically arrange the OCT setup to do that, and if I could the left supercardioid would face the audience more than I’d like.  So I choose not to use it there specifically because I want a form of imaging distortion that OCT was designed to eliminate.  I’d like to use it more in the right situation where I’ perfectly centered, the room is good, and want to capture the imaging exactly as it is in the mic location, but all that is rare for us.

I might try to do a split A-B pair of forward facing cards, with one card as the center on the OCT, and then the side facing supercard pair of the OCT.  That way I can mix the OCT attempt and still have a forward-facing A-B cardioid pair to use as a 2ch recording if I don't like the OCT.

That’s a great idea, and is sure to completely confuse any other taper with the two offset mic pairs. I’d move the forward facing cards a bit forward, and wouldn’t worry much about micro-delaying things unless you want to.

OCT though does seem interesting to me, in that the side-facing supercard pair seems to do what the split omnis do:  make an exaggerated stereo spread, with I hope would help with the typical center-panned PA system.

Exactly, and that’s something of what I heard in listening to the supercardioid pair alone, but interestingly it didn’t really suffer from over-wide-omni hole in the middle. I thought it interesting that the null of each side facing supercardioid mic points more or less at the opposing edge of the Stereo Recording Angle- similar to Blumlein, and the backwards facing opposite polarity lobe of each introduces low level opposite polarity information for any sounds arriving farther to the sides.  Pretty ingenious and elegant arrangement. 

I love Blumlein while also generally prefering mic setups that are not coincident, so OCT really intrigues me.  Though it seems a bit perfectionist in general for concert tapers.

Whew, another essay!

[newplanet7]

Some of my favorite 4 channel STRICTLY AUD tapes are 4 mic onstage mix downs.
Sweet omni/sub spread with cards in the middle.

[crossthreaded]

I made the jump to 4 channels about 2 years ago and I am very happy that I did.  I use it mostly for sbd matrix recordings but also use it for mic comparison and matrix of 2 mic sets.  It has really helped out when I can place omni mics on stage and use the house snake to run back to my FOB set of audience mics.

here is a show I taped last month that came out very nicely of some 184's and 460's.

http://archive.org/details/fb2012-03-23.akg461-km184-matrix

I've become friends with the owner of a local studio and he lets me borrow whatever mics I want from time to time.

I will warn you that immediately after going to 4 channels I realized that still wasn't enough.  Lately I have been borrowing Soul Intent's DR07 when I need to run 6 channels, but that is almost more work that it is worth so I will be stepping up to an 8 channel rig sometime in the near future.

[chinariderstl]

I am totally new to the 4-channel thing, but am looking into it.  Would you ever run split omni's (say 3ft apart) on the same stand, same location as your card pairs (say DIN in the middle)?  This is the mic matrix setup I am considering into an R-44.  I am, of course, also interested in doing a stereo board feed + a pair of cards into the R-44.

[acidjack]

I am totally new to the 4-channel thing, but am looking into it.  Would you ever run split omni's (say 3ft apart) on the same stand, same location as your card pairs (say DIN in the middle)?  This is the mic matrix setup I am considering into an R-44.  I am, of course, also interested in doing a stereo board feed + a pair of cards into the R-44.

You can read the thinking a bit further up in this thread, but I think a general rule of thumb is there is some validity to split omnis + a center pair, especially outdoors.  Less so w/r/t other combinations of just mics in the same location.  For example, I ran cards + hypers the other night, mostly to see what I liked better. The combined result is not better and sounds "odd".  Sometimes I have gotten results I liked by combining a bunch of mics on the same stand, but generally I think it's something to be avoided.  It also depends a lot on the flavors of mic you are combining.  I find that a super-bright mic like the Neumann 150s is good to pair with things if you are including the Neumanns to provide a lot of "upfront" sound and brightness; of all the multi-mic mixes I've liked many of the best have involved those mics.

I'd say the best uses of the extra channels are: (1) SBD+AUD, (2) Mics placed in various locations (miking actual instruments or people, or say onstage + FOB/DFC) and (3) split omnis + something outdoors.

For me, I do (1) the vast majority of the time. 

[Todd R]

I've just recently come across the Optimum Cardioid Triangle technique.  I've been thinking I might want to try that out, though it violates my policy of not arranging my mics to keep a 2ch "out" that I can always fall back on.
[snip]

Gut -- what was your experience with OCT?

Didn't want to forget you Todd before I shut up.

<snip>

Whew, another essay!

Thanks much Gut, esp for this, and for your other essays in this thread.  There are specific things I'd like to achieve with my attempts at 4ch mic recording.  I've attempted them numerous times, almost always with the same goal in mind.  I haven't gone into it without thinking at all about it, but haven't put anywhere near enough thought as necessary into it, nor investigated the theory as much as you.  I appreciate all the insights from your trials and your research.

My own attempts have had quite varied results, reflecting to a large extent that I'm never that serious about it -- it is always just a why-not-try-it thing to go along with 2ch recording -- plus I'm not motivated to really lug stuff out into the wild to make it happen, so I make do with whatever clamping arrangements I can make out at a show, and try to get as close as I can to the mic arrangement I'm after without bringing 3+ mic stands to a show or whatever.

On that basis, I am getting close to stopping the experiments and just focusing on 2ch recordings.  I really might though have to try at least a couple of times to do the OCT/OCT2 thing.  Seems pretty interesting.

Plus of course it would be great to confuse everyone with side-facing mics and odd mic pairings.

BTW, totally agree with you that running 4ch in the sense of two 2ch rigs not with the intent to mix the 4ch together but to learn and compare new techniques and equipment to the old tried-and-true stereo pair is a great reason to run 4 channels.  You can learn a lot and really better understand your equipment and your techniques.

[Gutbucket]

I’m back in town after some time away and wanted to add one more thing before the thread trails off, obscured by overgrowth-

While most of what I outlined above focus on avoiding problems in mixing multiple mics down to the same channel by getting sufficient distance (and/or angle) between them, there is another way to avoid those problems mixing two near-spaced pairs.  I mention this to not only complete the essay on ways to avoid problems mixing multiple mics down to stereo, but also because it may be the most practical thing to do for mixing two pairs setup the typical way on a single stand.

Instead of trying to get sufficient distance between the different microphones, you can go the other way and set up the two pairs so that the mic diaphragms on either side are coincident.  In other words, arrange the two Left mics with their capsules as close together as possible, typically one stacked directly above the other.  Do the same for the two Right mics.  You can angle the mics differently if you like.  In that way you have a Left1/Left2 coincident pair and a Right1/Right2 coincident pair, with only two physical microphone locations.

That arrangement allows for good comparison between the separate stereo setups by minimizing variables of mic position and pair spacing, while also allowing mixing the two without phase cancellations.  Similar to using a coincident stereo pair to assure mono mix-down compatibility, the coincident arrangement of mics on either side makes mixing the two stereo pairs less problematic by minimizing the phase differences between them.   That arrangement won’t provide the same benefits of combining multiple mics which are decorellated by sufficient distance, but there are other reasons which may make it attractive, beyond simple comparison. 

Combining the coincident pairs will alter the pickup pattern on each side as well as changing the sound timbre.  Mixing two coincident directional mics will morph between the two patterns (and timbres) depending on the mixing levels.  If the mics are pointed in different directions the virtual pattern angle will combine and rotate between them as well.. and might be useful in pointing one pair wider and the other closer to parallel.

Some specialty mics which contain multiple diaphrams and separate outputs for each work in this way.  Instead of providing a two channel stereo output from the mic, the output is two mono signals designed to be recorded separately and mixed to a single channel later while adjusting the pickup pattern as desired.  In that case one capsule is an omni and one is a figure-8.  By mixing them together in various proportions, the user can select any polar pattern desired from omni through cardioid to figure-8.  The user can also flip polarity on the figure-8 to point the mic in the opposite direction (but can’t otherwise control the virtual mic rotation).

Another use is extending the low frequency response of a directional mic buy mixing it with a coincidently located omni.  To do that without changing the pickup pattern of the directional mic above the reinforced low frequency region, the omni needs to be low-passed.  The filter used is typically an inverse of the low end rolloff of the directional mic.  That setup operates something like a speaker crossover-  Each mic operates in a separate frequency range with a smaller region of crossover overlap between.  Most of the information on the OCT setups I’ve seen using Schoeps mics discuss the option of adding coincident omnis with in-line low pass filters co-located with the Left/Right supercards to extend the low end response.

[F.O.Bean]

I love this thread I run 4chan and I DO NOT matrix the 2 sources together. I just like compoaring and enjoying the different sources on their own. And I have a DR2D to do those SBD/DAUD Mixes if I ever need to

LOTS of good info in this thread

[chinariderstl]

.

here is a show I taped last month that came out very nicely of some 184's and 460's.

http://archive.org/details/fb2012-03-23.akg461-km184-matrix

This sounds f*cking awesome!  Love those German mics!

I have AKG 481's (and 391's) but still want me a pair of KM184's. 

[acidjack]

.

here is a show I taped last month that came out very nicely of some 184's and 460's.

http://archive.org/details/fb2012-03-23.akg461-km184-matrix

This sounds f*cking awesome!  Love those German mics!

I have AKG 481's (and 391's) but still want me a pair of KM184's. 

You know there is that reasonably priced set of TWalker's still calling your name in the YS, right? 

[chinariderstl]

You know there is that reasonably priced set of TWalker's still calling your name in the YS, right? 

Oh, believe me, I know! I've been drooling over those since they went up.