Stereo vs 2 Channel
 

At the risk of sounding like a dumb question, can someone tell me what the difference is between recording with a stereo shotgun microphone vs recording with 2 mono mics on separate camera channels?

A stereo mic is just two mono mics inside the same shell. Good stereo requires more than simply recording two channels - it also requires attention to the levels and phasing of the left and right channels in order to provide the brain with the cues it needs to create the illusion of space. The main difference between using a stereo mic instead of two mono mics is you don't need to worry so much about mic placement and matching with a stereo mic. The downside is you don't have as much flexibility either.

Thanks Steve, good explanation.

Actually, the most important factor is probably in the physical arrangement of the two mics (and the exact specs of the two mics used). Stereo mics (or stereo techniques with two separate mics) involve mic capsules that are carefully chosen for how their frequency response and pickup patterns interact, and placed in a very specific configuration that allows them to capture spatial information.

Two channel just means you're recording using two sound-gathering devices - often placed on different sources. Stereo means you're using 1 specifically-configured 2-channel sound-gathering device, both aiming to capture the same sound source.

Stereo shotguns are not the best approach to stereo! You can get a much better stereo image using a good pair of microphones in a proper configuration than you'd get from a stereo shotgun. You can also use non-shotgun stereo mics to better effect. What are you trying to record?

Depends on what you mean by "1 ... device." I'd consider 2 cardioids or hypercardioids in an X-Y coincident array to be two devices, not one. Likewise a cardioid and a figure-8 in an M/S configuration or a pair of figure-8's in a Blumlein Array would be 2 devices or even a pair of omnis in an A-B spaced array but all of them are well-known mic arrangements for recording true stereo.

I brought up the question due to a discussion on another forum. I always thought I was recording stereo using 2 mono mics into my PD-170's audio channels. Someone else told me it wasn't true stereo prompting my question here for the experts. I'm a wedding videographer and this question applies to capturing reception music and ambient sounds.
Thanks for the input.

And plased be advised that the term is Stereo/Shotgun, as in stereo OR shotgun. There is no such thng as a Stereo Shotgun.

Regards,

Ty Ford

Bob, to clarify a bit more--
In the most common usage, especially around here, the word stereo means recreating the sense of relative placement of sounds a single head would hear at a point in the room--a stereo image.

But two mics that provide different signals two the two channels, directional mics pointed differently or nondirectonal mics located differently, can often give a spacious and pleasing sound. I don't think you're wrong to call that stereo sound in the dictionary sense. You wouldn't get a true stereo image, but that is probably not important for a wedding reception.

But for recording a stage concert, you might want to take two directional mics, say cardioid pattern mics, line them up with one directly below the other pointed at the stage, then rotate them while keeping the front ends lined up so that one points toward the front left and the other toward the front right. They still receive the same sound waves at the same time over all frequencies, but each one's response is strongest in the direction it's pointed. Meanwhile, the response of each mic to the sounds coming from the front center is weaker, BUT it's heard from both speakers on playback. The relative loudness and locations of the sounds, aka the stereo soundfield, is reasonably reproduced. This arrangement of mics is called the x-y coincident pair.

A lot of stereo mics use a pair of fixed X-y coincident elements, but in return for the convenience you trade away the flexibility of being able to change the angle to get the balance you want. There are other arrangemets that reproduce the soundfield also.

Well, I thought I made that clear in my post - that my definition of "1 2-channel device" included "two seperate mics in a specific configuration" as opposed to "2 separate devices" which don't have a specific relative configuration.

Just semantics... but even when I'm using a spaced pair, or a Decca Tree, I consider the whole setup to be one stereo device, because of the various types of constraints (on mic matching, placement, levels, etc.) that tie the system together. MENTALLY, I mean, a stereo pair is a single device working on 1 consistent image, while "2 mics" can also be 2 unrelated devices working on 2 unrelated images.

Then there's creating a stereo image with non-symetrical mics; like using a Schoeps CMC641 and a Neumann U 89 on the top and bottom bouts of an acoustic guitar, respectively. Semantics preclude some from calling this "stereo" due the dissimilar mics, but the stereo field created can be quite nice.

Regards,

Ty Ford

Scratching my head on this one and looking at my A-T 835-ST.

the 835ST is EITHER a stero mic OR a shotgun. Not both at the same time.

Ty Ford

I am missing something Ty. In the definition of Shotgun, does it only specify mono? On narrow or wide, it is stereo. It has the 'reach' of a shotgun (rejection is the better term, I believe). There is also the M/S, which is different.

Not to put words into Ty's mouth but what I think he meant by that is that a "shotgun" typically is picking up from directly where it is aimed and has relatively little pickup away from the centre axis. A stereo mic, OTOH, pickups from a broad area in front of the mic in order to create the stereo soundstage. The focussed directivity of the shotgun is conceptually the exact opposite of the broad pickup pattern (when both channels are considered) of a stereo mic. The "stereo shotgun" when used as a shotgun would not be creating a stereo image even though sound might be present on both channels - the left and right signals would be substantially the same unlike the case with the same mic set for stereo where the two channels are quite different.

Yes, mono only for shotgun. Otherwise the added side stereo capsules (X/Y or M/S) make it a stereo mic.

The more stereo you have the less rejection you have, by definition.

'
Regards,

Ty Ford

Pretty much. Look at AT's description.

At 9.29" (236.0 mm) in length, the AT835ST provides broadcasters, videographers and sound recordists professional quality stereo audio in a microphone that resembles a monaural shotgun mic. That means the AT835ST is easy to use with standard camera mounts, shockmounts and windscreens. Engineered for long-distance pickup in broadcasting and film/TV production, this compact M-S stereo shotgun features internal matrixing innovations that allow for stereo audio with or without an external matrix. It also features switchable low-frequency roll-off and independent line-cardioid and figure-of-eight condenser elements.

"THAT RESEMBLES A SHOTGUN"

The idea that a stereo shotgun is a mic that has two far reaching lobes is erroneous.

Regards,

Ty Ford

Hi Ty.

I'm not arguing - I've just never used a stereo/shotgun mic. I've done a lot of MS recording, with a variety of Mid patterns, and I'm familiar with the math of the "virtual" stereo signal.

So, theoretically, by math, and empirically, based on MS recordings with everything from omni mids to hypercardioid, it seems vaguely possible that a shotgun + bidirectional could give some sort of stereo effect with more reach than a cardioid or hyper M MS setup. If you've played with the math, the virtual mic looks like two farther-reaching lobes.

Now, I know this is extremely dependent on mic placement (since the side pickup may very likely be exposed to things the mid is highly rejecting, as distance to source grows). And I'm not sure there's a clear definition of "shotgun"... but it seems like something at the far-reaching end of the MS continuum is not implausible.

Again, I've never used one of these... I can imagine that they just don't work well in shotgun situations. Just curious what your response would be.

If you only have one forward-facing element (and every stereo/shotgun I've seen has only one) then it's not possible to have two forward lobes.

Regards,

Ty Ford

I agree with what Ty posted regarding two forward-facing lobes.

Looked at another way, the side element of an M-S config. is a figure-8 element. Let's say we do what Barry suggests, and use a shotgun for the mid element. Ignore for a moment what that sounds like (I've not tested it) and let's consider directionality.

We still have the side element, basically not directional at all. Any sort of M-S array is sub-cardoid in response. Seeking side rejection, we start decreasing the volume of both the plus and minus side signals.

Voila, we have increasing side rejection. BUT, we're losing stereo effect. By the time we've decreased the side volume to the point we have the directionality of a shotgun mic we have no meaningful side information nor any stereo image - we've got what Ty suggested several posts ago, a mono shotgun microphone.

I guess the math that Barry is doing indicates that Side plus a shotgun Mid looks more directional on paper than Side plus a cardoid Mid. I can see that, but I believe that is purely at the expense of stereo image.

If you wanted the same stereo image with a shotgun Mid as acheived with a cardoid Mid you'd be adjusting relative gain M vs. S to the point that math shows the same polar response (as a rig with cardoid Mid). That is, you'd decrease the Mid gain relative to the Side gain, losing apparent side rejection. Except the image may fall apart due to the increased directionality of the Mid element - I've not tested it.

Well, I've got it clear in my head but it's difficult to write about. It'd be easy to demonstrate and diagram. But hey, you might like the sound of a shotgun Mid element and decreased Side gain - if it sounds good, it is good.

I've certainly struggled with a big mike stand in the 3rd or 5th row of an audience, but screw 'em, good sound is worth it, right? ;-)

I really get pissed off when some "picture" guy says we can't have a mic there, it's in the shot. Where are their priorities?

Just kidding, but not really. There is certainly tension over these issues, and I'm always looking to fly mics, or lower profile mics, or some way to keep the mics where they sound the best.

"We have met the enemy, and they are us." - Pogo

I see part of the issue here with how we are looking at it. I think you guys are thinking stereo by spliting the head in half and out the ear on each side is the 'center' for each?

Consider a marching band on a football field in front of you. The contras (tubas) are on the right, the drumline (battery) is on the left and the tenors (trumpets) are in the center. The elements are 90 to 120 degrees apart and at 45 degrees apart. You hear the texture and they can play with serious seperation. All of the main elements are in front of you. You do want to reject anything else. And it sounds flat in mono while not matching what you are seeing.

The best setup I have seen is a cross over pair at the 50, and a left and right at the 35. They also do a couple at the crowd and maybe one on the opposite side (the band will play away for soft sounds). I think I remember it like that at DCI finals, although they may have also had to mics at each 45 too.

Me, I get no setup time and run onto the edge of the field. I need to capture stereo to catch the texture and reject side and behind. What would you use? ;) Stereo shotgun? :P

5.1 is better because you can get in the 'middle' of the field. Too much stuff to carry onto the field with <2 minutes to setup.

Side note, I bought Mr Videos disc of the semi-finals this year. I was on the DVD on the sidelines at Gillette Stadium. :D

...then perhaps you're not familiar with the math... (see, for example, www.wesdooley.com/pdf/technique.pdf, or Streicher and Everest's Stereo Soundbook). As you'll note, I said "virtual". For example, MS with two bidirectional mics yields a "virtual" mic setup identical to a Blumlein pair, with "virtual" lobes at 45 degrees. With an Omni mid, the virtual lobes are closer to 90 degrees. As the mid gets more directional, and of course depending on the MS ratio, the angle of the virtual lobes closes towards 0 degrees, and the reach extends. At the extremes, of course, are pure mid-pattern, and pure bidirectional. However, it's a smooth continuum.

Again, I've never used a "stereo/shotgun". But the whole point of MS is that it indeed provides "virtual" forward facing lobes, and the width and reach of the image can be adjusted by the MS ratio. Cardioid has more reach than omni. Hyper has more reach than cardioid. And, I'd assume, shotgun just adds more reach on top of that.

The stereo image, though dependent on the situation (esp. how close the mic is to source vs. side "distractions"), of course tends to get a little strained when the mid is more diectional than a narrow cardioid, but again, it's a continuum. There are indeed still "virtual" lobes with a shotgun/8 combo, and they're reachier and more forward-pointing. They may just sound like crap. It may be hard to match shotgun and f8 frequency responses. There are likely many reasons why it's not a great approach... but it's still a point on the MS continuum that's as much MS stereo as any other combo....

This is true if the mid is cardioid... if the mid is a hyper, the response can be narrower... with a very small amount of S! But it can add a bit of richness.

Guys, just in case - I'm NOT advocating the use of a stereo shotgun or stereo/shotgun. At least not for any situation I could think of. I'm just exploring the supposed "impossibility" of such a thing. It's not impossible; in fact, it's not at all out of line with any other form of MS.

Barry,

Go out an get a shotgun and leave your theoretical universe for the real world.

Now you're talking about Wes Dooley and TWO Bi-directional microphones.

SHOTGUNS AREN'T MADE FROM TWO BI-DIRECTIONAL MICS.

I think you have expended the universe.

Ty Ford

Oh, c'mon, Ty, you trying to be difficult? I'm discussing the continuum of MS techniques from Omni through Hyper I've used in the real world with great frequency. A shotgun-mid MS setup is the only theoretical leap, and not a big one.

What do you have against Wes? I'm just pointing you to some of the seminal papers. They're nice! Read 'em.

Anyway, thanks, though! I have ALWAYS wanted to expand the universe! I'm gonna go stretch it some more.

I wouldn't use a directional mic like a shotgun at all. You'd get too much of what is in front of the mic and not enough of the other 2/3 of the band that's off to the Northwest and Northeast relative to the camera. Do you have an assistant that can handle a boom? Put a hypercardioid and a figure-8 in an M/S pair on the end of your boom or in a pistol handgrip and when you dash to the edge of the field, assistant stands to your side and points the "mid" mic in the same direction your lens is looking. I've heard that European productions often use M/S pairs on a boom pole.

That is why I use the 835ST. No assistant to boom and it has the field covered in a hurry. I miss the other end if I am close to the sideline, but can't help it in cases like that. I can put it on a stand and get it closer to center, but not always. At the recorded events, I do not have any leeway as I do not control the field and have a 'box' I am in.

Anyway, FYI, Electronic Musician is focusing on MS techniques this month, for anyone who wants something a little less techy than the articles/books I referenced...

Then there's mics like the Sanken CSS-5, produces a 'directional' stereo field. Takes 5 elements to do it and not exactly cheap.