Tim Nielsen Special: MS Recording
[Written by Tim Nielsen]
I’ve been recording with MS since I started in this industry, about 12 years ago now. There are of course many other recording techniques available, and I own microphones suited to most of them. I tried to elaborate a tiny bit on some of the other stereo techniques in my previous article, and that’s when I realized that MS really needed it’s own article.
Of all the stereo formats I record in, MS is my favorite. I find it to be the most compact, and by far the most versatile, of all the stereo recording techniques I know. It’s also a bit tricky to wrap your head around the first time you try to understand it. I remember at USC the day I asked Tom Holman, creator of THX, to explain something about MS that had been puzzling me (probably the entire idea behind it and how it worked at all). For the next hour or so, he proceeded to draw math equations on the dry-erase board. I sat, staring and dazed, occasionally nodding to feign understanding. The fact is, MS is a strange recording method.
I’ve had quite a few people, even ones I work with, tell me they don’t like MS, but many times it seems to me that they can’t tell me why. Maybe it’s simply that it’s a bit too much like voodoo. But properly done, MS recording is basically another form of XY recording. David Farmer and I, while both in New Zealand, did some tests between his Schoeps XY microphone, and my MS rig. Neither of us could hear much difference, and my memory is that both of us slightly preferred the MS rig when we felt we could hear any differences. There is really nothing to be afraid of with MS.
For those who don’t know, an MS rig consists of two microphones (or more, as there is a Schoeps Double-MS setup and I’ve personally set up and tried a Triple-MS rig of my own Frankensteinian devising). In the stereo version, there is a Mid microphone, and a Side microphone, hence the name MS Recording, or Mid-Side Recording. The mid microphone faces forward, and can be of any pickup pattern, although almost always a cardiod or hyper-cardiod microphone is used. The side mic is always a Figure-8, or bi-directional microphone, whose polar pattern is perpendicular to the front facing microphone. The two microphones are ideally very well matched, and most of us use mid microphones that have in their family a Figure-8 version as well, for instance the Schoeps MK series of capsules, the Sennheiser MKH series, or the Neumann KM100 series with AK capsules. All of these have cardiod, hyper-cardiod and Figure-8 mics available and are ideal to use in an MS setup. There are also self contained MS microphones, made by companies like Pearl and Sanken, or the Neumann RSM-191, which I know several people here use. The only reason I tend not to like microphones like the RSM-191 is that they use external powering and matrixing boxes, which I find cumbersome. But the RSM-191, the Sanken CMS-7 are very nice sounding MS microphones as well.
You can see pictures of my two MS rigs in the previous article on microphones. My rigs consist of separate microphones in an MS array, rather than a single MS microphone. In my case my first MS rig consists of a Schoeps CMC6XT / MK41 hyper-cardiod mid microphone, with a CMC6XT / MK8 side microphone. My second rig consists of a Sennheiser MKH50 hyper-cardiod mid mic, and an MKH30 Figure-8 mic.
So how exactly does MS work? Basically through some summing and phase manipulation, you can derive from the two channels, a stereo image, which will sound about the same as an XY rig aimed somewhere between 60 and 120 degrees apart. Rather than explain too much how exactly it works, I’ll simply link an article on WikiRecording that explains it better than I could.
So why record in MS instead of XY, ORTF or any other method? I’ll list some of the advantages, but first I’ll admit there are a couple of disadvantages. Let’s get them out of the way first.
The first major disadvantage to recording in this format is that MS Recording requires processing after the sounds have been recorded. This is because what you are actually recording is a forward facing microphone, and a side facing microphone, or two mono channels. Only though some summing and phase manipulation can you turn this into a stereo recording. Many recorders now have the ability to do this during the recording process, and many single MS microphones can do this internally or through the use of an external box (like the Neumann RSM-191), but most of us who use MS prefer to process the sounds in ProTools. The Sound Devices 722 that I use actually has a brilliant feature to decode MS only to the headphones, allowing me to record the raw channels, but hear the decoded stereo channels. I prefer to record MS as the raw mono channels, load the files into ProTools, and master them into stereo files. Processing consists of either using a plugin such as Waves S1 Imager (there are others) or else building a set of tracks to do the MS Decoding. If people here are really interested, I’m happy to write another article explaining more the details of building MS mastering tracks in ProTools. Just make some comments here if you want that kind of thing.
The second disadvantage is that if you decide not to master the MS recording into usable stereo, and store it as an MS file, and forget, you might have problems later. This is because the two channels of an MS recording won’t sum nicely together into mono. In fact the phase will be all over the place. If later you forget that a file in your library is MS, and you use it as stereo, you might not actually catch it just by listening to it. I’ve found that even raw MS files can dupe your ears into thinking it’s stereo. But later, especially in a film environment, in a mix for example, those channels maybe get summed together, and result in a very strange phasey sound.
But now for the advantages, and this is where it gets fun, and why I’d really encourage that your first rig or main rig be an MS Rig.
First, for a stereo recording rig, the MS system can be quite compact, compared to say XY, ORTF, Spaced Omnis, etc. Because the two microphones are placed one above the other, it’s quite easy to fit an MS Rig into a single Rycote zeppelin, even one designed for a mono microphone. In the pictures in the previous article, you can see that in practice, the smaller rigs are Schoeps rigs in mono Rycote suspensions. Unless you’re building a miniature XY set, or using a compact XY microphone, MS is going to provide you with the most compact rig.
Secondly, in an MS rig, you always have a forward facing mono microphone, and for a lot of general effects work, this is incredibly helpful. I mentioned in the previous article the usefulness of a short or medium length shotgun mic, like the Sennheiser 416. While this is true, most of the time, I’m perfectly content to use the hyper-cardiod mic in my MS rig as my mono effects microphone. The MK41 Schoeps, and the MKH50 Sennheiser in my MS rigs are not as directional as the 416. But they are actually close. Close enough for a lot of what I want to record. I’ve built some cables to connect my stereo rig in the Rycote to just one input on my 722, so I can easily use my stereo rig as a mono rig, the cable simply dropping the figure 8 channel out of the way.
Third, MS allows for post processing of the stereo image width after the recording. This can be quite useful. This is done by varying the amount of the side microphone signal against the amount of the mid microphone during processing. Pull the side microphone out completely, and you’re left with only the forward facing microphone going to both channels. Adding the signal from the side microphone back in adds width to the stereo image. This is over simplified, but the advantage of MS is that you can vary the width of your stereo image.
Fourth, a small one, but because the microphones in an MS rig are coherent (the capsules aligned vertically), stereo files derived from an MS recording are fully mono compatible, which can still be important in the film sound business. XY recordings are mono compatible too, but other methods like ORTF or Spaced Omni recordings may not be.
Fifth. OK, I’m going to reveal one of my best kept secrets. Quite some time ago, I realized something. If you’re recording in MS, you’re not recording in stereo. You are in fact recording in LCR. Think about it this way. If you recording a forward facing microphone and a side microphone, and then use them to create two stereo channels which behave like XY recording, then what happens if you add back in the raw mic microphone? Think of the screen channels across the front. Decoding the MS files into stereo give you the Left and Right. The mono forward facing microphone can give you the back the Center.
I now master most all of my MS recordings into LCR instead of stereo. Again I’m happy to build a walkthrough on how to do this in ProTools. It’s not complicated, but there are a couple of pitfalls to be avoided. But I’ve found it incredibly useful. First, LCR recordings are very useful in film. I’ll give you an example. When recording backgrounds, say you record something in stereo. Now you take that material to the mix stage. One thing that mixers tend to do, is to pan in the stereo channel to get some bleed into the center channel. They do this because they need help masking the natural background of the dialog. But this results in your nice wide stereo background now being panned into something less wide. If you instead have a natural LCR file, there is no need to pan in the sides, instead, the mixer will have a natural center channel to be brought up to fill in the center channel. I find LCR backgrounds sound incredibly natural. Things panning across now pan from Left, to Center, to Right, for instance, and the sound image for film use is very smooth and very natural. Crowds sound brilliant in LCR, as do city backgrounds, just about anything really. Just as stereo is a huge improvement over mono, I feel like LCR is a big improvement over stereo.
The other great thing about mastering your MS recordings into LCR is that you are then preserving that forward mono facing microphone. Need a mono version of the effect? You already have it, just use the center channel by itself. When mastering into LCR, you will be placing the raw forward facing mic as the center channel. Need a stereo version, no problem, just drop the center channel of the LCR and you’ll have the normal XY version of the sound. So what you are preserving is a mono, stereo, and LCR version all in the same file. Later versions of Sound Miner will supposedly allow you to just select the left and right channels of an LCR effect for spotting right to a stereo track in ProTools. This will be very useful. For now, I tend to spot to an LCR track, and from there, drag it down into three mono tracks, to allow me to work with the LCR file. It’s cumbersome, but still useful enough to me to make it worth doing.
And if I haven’t confuzzled you enough (for the definition of confuzzled please see the brilliant stop-motion film Mary and Max), here is where it gets really interesting. Imagine an XY rig, consisting of two microphones, the forward facing mono mic, and a Figure-8 microphone. Now, imagine we simply add in another mono microphone, but this time, facing backwards, in the opposite direction to the forward facing microphone. By adding in only one more microphone, we have actually now created another MS pair. This is because the side microphone will also still be facing perpendicular to the newly placed ‘rear’ microphone. It only requires the phase to be flipped the opposite way, and it will work to create backwards facing channels. Schoeps actually makes a microphone doing exactly this. It’s very expensive, but with only three channels, you can derive a quad recording.
But wait, if I told you earlier that recording MS is really recording potential LCR, then a Double-MS rig must be recording Double-LCR, or the ‘potential’ for them. A Double-MS rig can actually be decoded into Left, Center, Front, Left Rear, Center Rear, and Right Rear. Six channels can be derived from just three recording channels. This is very easy to do, once you’ve built a template in ProTools to do it.
Still with me? A few years ago, while living up in Vancouver, I had a crazy idea. To understand it, remember that I mentioned that you could use any polar pattern as a mid mic, but that mostly a cardiod or hyper-cardiod microphone is used? Now imagine we build a simple MS rig, but this time with an omnidirectional mid microphone. What this actually yields are two channels, aiming 180 degrees apart. Or imagine that using the omni, you create a stereo image that follows the polar pattern of the Figure-8 microphone. So back to my crazy idea. I realized, that in a Double-MS setup, adding in a fourth mic, an omnidirectional one, would allow me to derive two more channels, a hard left and a hard right. And actually, the omnidirectional mic itself would be placed right in the center of the image, and could be called a true ‘center’ channel, or top channel for instance. Also, since the omni would be very flat down to extended frequencies, I could use it to derive a .1 channel if I wanted. So what I came up with was that a Triple-MS rig (consisting of two hyper-cardiods, one Figure-8 and one omni) could really record 9.1 channels of info into four recording channels. With it, you could derive the following:
True Center, Left Front, Center Front, Right Front, Left Rear, Center Rear, Right Rear, Left Side, Right Side and LFE.
I am the first to admit that this is silly and fairly useless. But it does indeed work. I set up a Triple-MS rig with the Schoeps, recorded some city sounds, and mastered them in that format. I didn’t have the proper speakers to hear it in it’s full glory. And I can’t say for sure how great the separation of channels would be. And the truth is, in film work, you find that most multichannel recordings don’t sound ‘wide’ enough, so you for instance cheat another sound for the surrounds in an attempt to create that wide spacious sound you want. But hey, I love to do silly things to see if they work, and I can say that with a ridiculously elaborate ProTools session, you can indeed master four Triple-MS channels into 9.1 channels of sound.
That then is a little MS primer. Post any questions in the comments below. Later when I’m home from traveling, maybe I’ll make a screen capture movie showing MS mastering in ProTools, I don’t have ProTools with me at the moment.
But I hope that might give you some ideas of what you can do with MS.