ORTF/MS Phase question

Discussion in 'Location Recording' started by hp1xbg, Jun 10, 2011.

  1. hp1xbg

    hp1xbg Active Member

    I have a wind band recording I am working on (70 piece). While it is quiet, the room isn't that great, so the "hall" isn't helping so much.

    I have a pair of DPA 4011 in ORTF and a Schoeps MK4/MK8 MS pair on the same bar. I put them up just to A/B them. I have outriggers, but am not using them very much....they are Cardiod Schoeps MK4. There are various spots in the ensemble as well.

    I usually like the sound of the DPA's, but everyone that has listened to the pairs likes the MS pair slightly better as the image seems to be sharper, at least in the middle. I prefer the depth of the DPA's better. So here are my questions:

    1. I am not mixing ITB and do not have a phase meter. If I reduce the MS pair to mono while using the cardiod outriggers, am I going to run into problems? (I didn't use omni outriggers because I wanted to keep the room out of the recording. It's a great rehearsal space, but square/drywall sides make it sound like a gigantic living room.)

    2. I have read often that folks put up an ORTF pair and a blumlein pair on one stand for choir micing and wind up blending the two. Can I do this with the DPA and the MS pair. or I am creating a holy nightmare of phase problems? When I blend the two in stereo, they sound good....

    Thanks....I just wanted to ask some other opinions.....
     
  2. BobRogers

    BobRogers Well-Known Member

    Every micing technique that's not exactly coincident will have phase "problems." Those "problems" are a big part of the stereo image. That's not to say you should ignore phase problems, but worrying about them shouldn't prevent you from experimenting with all combinations of these elements. Basically, you tell us - what does the ORTF/M/S combination sound like?
     
  3. Boswell

    Boswell Moderator Distinguished Member

    An MS pair reduced to mono is just the M channel with no S present. If you were to treat the M channel as a centre-fill for the ORTF pair, it should work. I don't think M channel plus the outriggers and no ORTF pair will give you a satisfactory image.
     
  4. mberry593

    mberry593 Active Member

    I have a few MS points to discuss. I have never tried to do an MS recording but the concept does interest me. I do understand the principle & it does seem to me to be an excellent way to do things but I have some problems with the actual implementation. Please understand that since I have never even tried it, it don't know what I am talking about so I am here for some education from those that have.

    First of all there are things like the SM69 & AT 4050ST. I assume that they are ok but that's not what I want to talk about. I am interested in using two microphones mounted next to each other.

    The problem as I see it is that most (maybe all) microphones have significantly different responses for different patterns. For example, if you have two U87s and set one for cardoid (M) and the other for figure 8 (S), you will get a brighter sound in the middle than in the L & R sides. That seems to me to be a big drawback but I don't know.....someone tell me if this is a problem in your experience.

    Now you could set up two instances of Antares Mic Mod and set one to do nothing (not bypass, same in and out) and the other to convert the sound of one to match the other. This would solve the frequency balance problem nicely but at what price? You don't get to play with freq. balance without messing up phase relationships (lacking big DSP) and the whole MS concept is based on phase relationships. It would seem to me it you tried this trick, the geometry (soundstage?) would suffer. Has anyone tried this? If not, would anyone with MS experience like to give it a shot and report back. Antares has free demo trials (ilok required) so the experiment should be free.

    Can anyone point out any commercial recordings that they know were done in MS with identical mics? If so, I might purchase them and play with them myself. I do have Mic Mod running here.

    Thanks
     
  5. TheJackAttack

    TheJackAttack Distinguished Member

    Why is this a drawback? One does not "hear" the same from the side as one does from the front as a binaural being. M/S is a very frequent classical coincident stereo pattern. Yes a U87 in cardioid does sound different from a U87 in figure of 8 but that is not a problem. Generally mic's as similar as possible are used and sometimes two figure of 8 mics creating the so called Blumlein M/S. This works VERY well for smaller chamber groups or for placing in the center of arced choir. I used M/S last March as the close pair (4' distant 5' high Royer SF12) for a grand piano lenten recital. I also had a pair of spaced omnis about 16' feet back and about 12' high. One delays the close pair to coincide with the back pair and can create wonderful recordings in this manner. One thing I did forget on this particular live concert was the slap echo from the side walls. It normally isn't a problem but this particular church is peculiar like that and I forgot. At any rate, M/S alone can create a fine full image. I refuse to use artificial reverb unless I have to so I normally have a "hall" pair to create any "missing" verb.
     
  6. mberry593

    mberry593 Active Member

    hmmmmmm

    What if we did an ORTF setup and used a Shure SM9 on one side and a Shure SM58 for the other. That would sound strange. One side would be brighter in comparison to the other. What's the difference here? In the MS case above, the middle is brighter than the sides. (Let's not belabor 'brighter' ... I know it is more complicated than that)

    Well the difference is that with the MS, it is symmetrical. I can see how that might ameliorate the difference. After all when we hear things in nature, the head blocks the sound to the ear from the other extreme side and that results in more of a high freq block than low. Do you think that is what is going on here?

    Again, I don't know what I'm talking about. I haven't done this. I'm just trying to understand if this differential frequency response thing is significant or not.

    I think that I'm going to set up a matrix in my DAW & take apart some instrumental stereo recordings that don't have a lot in the middle like a vocal would and play with this.

    JackAttack: Thanks for your response. You have experience, I don't. I value your comment that the differences are not a problem. I'm not trying to do an argument here, just a discussion so I can learn. This technique appeals to me so much that I am considering spending some money so that I can do it & I want to know what I am doing before I proceed.
     
  7. Boswell

    Boswell Moderator Distinguished Member

    Interesting discussion. I use MS form of some sort in roughly 25% of my recordings, and within that pattern have employed many types of microphone combinations. Regular members will know I have been a champion of what in these forums I have called "MS Blumlein", i.e. a pair of figure-8 microphones with one mic facing front-back and the other sideways. These could be either LDCs or ribbons. I have also experimented with the "3-cardioid" form of MS, where the S-channel is formed from an appropriately-phased pair of cardioids pointing E-W.

    I have to say that, in general, I prefer the mixes I have done when I used the same type of mics for the M and S channels, even though (in the case of LDCs in conventional M-S) the patterns may be switched differently. Many of my early serious experiments with this type of recording used a pair of Rode NT2-As in cardioid (M) and fig-8 (S), and I keep going back to listen to those tracks. At first it was to convince myself how much better my later tracks were using different techniques and more expensive microphones, but I came to realise that once you got above a certain standard of sound, it was not a case of "better" in sound quality, but "better" in terms of knowing the right mics to choose and techniques in placement and pattern selection for the particular performers and venue acoustics.

    One big factor that is often overlooked in mixing microphone types for M-S is that if you use a pressure-sensitive mic for one axis and a velocity-sensitive mic for the other axis, you get a 90 degree phase shift between the axes that requires considerable care to deal with. It's relatively easy if you have a preamp such as the Audient Mico that has a continuously-variable phase control, as you can dial the 90 degree correction straight in at the time of recording, and this means that monitoring (via a normal M-S decoder) gives you an accurate picture of the sound field. Otherwise, it has to be processed at mixdown, and I'm always reluctant to leave it that late.
     
  8. mberry593

    mberry593 Active Member

    Thank you! Very, very interesting. I'm new here so I haven't heard of these techniques before. They both can completely eliminate any concerns of different responses. I am very interested in trying these approaches. Can you direct me to any commercial recordings that you know were made using these techniques?

    Also your comment about phase correction is well heard. Does anyone know of an RTAS (or AAX HA!) plug-in that manipulates phase like that for us ITB people? I guess it could be done with very short delay or sample offsets but that is really awkward.

    Thanks again for your helpful comment.

    EDIT: I know about the Tritone phase plug but as I understand it, that is no longer available.
     
  9. TheJackAttack

    TheJackAttack Distinguished Member

    I see your point inre the SM9 et alia. People utilizing M/S technique are generally doing so with high quality condensers or ribbons. We do try to have a pair of the same (some only use "matched") microphones or at least very similar to each other. A pair of U87's or a pair of C414's are pretty normal as well as a pair of ribbons. One normally would not use moving coil dynamics for this at all not least of which because of the resultant lack of sensitivity to the "side" image off axis. The slight-and it is slight-difference in a U87 from cardioid mode to figure of 8 is quite negligible in this scenario although with the AKG C414, some versions are by design different on the back capsule from the front capsule ie "darker". It will still work but one has to know that going into the setup and the post production.

    While I can't think of any recordings 100% done with m/s, chances are good if you listen to solo piano literature or small chamber ensemble or vocal music you have heard M/S in action. The three most popular coincident or near coincident patterns for large scale classical recording are Decca tree, Blumlein, and ORTF/NOS. M/S and the spaced omnis are utilized often as well but maybe for medium sized and smaller productions.

    Rarely if ever is classical oriented music recording track by track even if spot mic's are utilized in orchestras.
     

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