Using a stereo mic- are they your choice as a sound pro?

[Richard Crowley]

Excellent. You have come a long ways and now have a good working stereo mic and mixer. You have demonstrated that you understand the strengths, weaknesses and peculiarities of stereo mics. We award you a solid "A" on this course! Congratulations. :-)

As you say, you CAN use the stereo microphone as a conventional monaural microphone by simply selecting ONE of the channels (leaving the other one disconnected) and aim the microphone properly to be ON AXIS with whichever channel you picked. Hopefully by now you have done the experiment and know what the "on axis" angle is for the left and right sides.

And indeed, I have seen some people use them in a hand-held interview situation where they keep one side pointed at the subject, and the other side aimed at the interviewer. That is kind of difficult to do effectively as it is NOT intuitive because you can't see the axes. You must remember to keep it in just the right position as you/they are talking, etc.

[Greg Miller]

Jonathan,

It's good to see that you are starting to grasp things; you've learned a lot in a few weeks.

Your last post asked some good questions; regrettably, the answers that you guessed at aren't quite right. So I'll try to shed some more light on the subject.

Let's consider a single mic, with a cardioid directional pattern. (50 years ago, very detailed patterns were published, and it was easy to see what was going on. Today, you're lucky if you get any published pattern at all. So you're not to be blamed for not already knowing this stuff.)

A cardioid mic is, of course, directional... it picks up more strongly directly in front of the capsule, and the pickup falls off to the sides. But what is not obvious is that the directionality is different at different frequencies! (And, incidentally, this will not be exactly the same for different model mics.)

Consider the attached set of polar response curves.

Start with the black line, representing the pattern at 250 Hz. Note the shape of the curve.

Now compare the dark blue line (500 Hz) the green line (1 kHz) and the red line (2 kHz). Note that as you go up through those frequencies, you start to get a little bit more pickup behind the mic. Subtle, not a big problem for most applications.

But look what happens to the cyan line (4 kHz) purple line (8 kHz) and especially the yellow line (16 kHz). The sensitivity at the sides of the mic starts to fall off significantly, as you go up in frequency! So when you're off axis to this mic, the high frequencies will be diminished and the sound will start to sound rather dull.

That's why you want to use a single cardioid mic element, pointed directly at the sound source (i.e. the talent).

Having said all that, let's consider the AT 822. Based on your questions, I think you're assuming that the two mic elements are each pointed 90 degrees off the physical axis of the mic body. That's very unlikely. They are probably each about 45 degrees off the axis of the body, in other words 90 degrees apart from each other.

When you seemingly point the mic (body) directly at your talent, he's actually 45 degrees off axis for each of the two mic elements. If the elements in your mic had the same polar response as that published diagram, then each element would be about -9 dB at 16 kHz, and your audio would sound dull as a result! (However, the sample curve is not for the AT 822; and I don't have a good set of polar curves for that mic; it will be somewhat similar but also somewhat different from the sample curves.)

Now, as far as your two-person interview scenario: If you could position the mic so that each person was off to the side of the axis of the mic body by about 45 degrees, then yes, you would get fairly good pickup on the two people. But it still would not be a great track. Because person "A" would also pick up on mic element "B" but with very reduced high frequencies. (He would be 90 degrees off axis for the other mic element.) You would have poor isolation: each person would be on both tracks. And if you made a continuous mono mix of the two tracks, it would sound dull, because you'd be mixing two versions of each person: one version "flat" and the other person very muddy. The only way to produce a really good finished result would be to edit, cross-fading between mics as the two persons alternated speaking (always using the correct channel for the given person).

And your scenario with three persons on each side of a table... bad. Again, the mic elements are not 180 degrees apart, they are only about 90 degrees apart. So there's nowhere that you could place that mic, that would even begin to get everyone on axis of one element or the other.

Unfortunately, as you learn more about sound, you'll learn that it's not as easy as you initially thought!

Does this make sense? Does the color image of polar response curves help?


PS: What's wrong with taking football action shots with a 4x5 view camera? I've done that. (Oh wait... that was 50 years ago.)

PPS: Can anyone tell me how to get an image up in the middle of the text field, instead of at the very bottom? Thanks!

[Richard Crowley]

In further support of Mr. Miller's excellent discourse...
Here are two diagrams of the polar pattern of the AT822. One is the black/white original, and the other shows my crude attempt at highlighting the left cardioid pattern in green, and the right cardioid pattern in red.

As you can see from the arrows I have drawn, the cardioid patterns of the left and right capsules are each 45 degrees off-axis from the body of the microphone. This is a classic stereo microphone design. As we have said before, you actually have TWO cardioid microphones in a single body. Like a two-headed monster.

[Gary Nattrass]

And to go back to the original question this is why as an sound pro I prefer to use an M/S stereo microphone as the forward facing capsule is always on axis to the sound source!

[Jonathan Levin]

Guys,

You are truly amazing! But stop! I need to study especially your last few posts. Thanks you so much.

Jonthan

[Paul R Johnson]

Like Gary, I like M/S - BUT it really isn't suitable for a beginner. Unless you have a recorder with a built in matrix, you can't use headphones for anything other than making sure there are two separate channels live, and even using it in some editors is very tricky, unless you can cobble together a decoder - which isn't hard, but you have to now what you're doing, and able to gang together faders that track together accurately.

Orchestral and choral events are ideal for M/S systems where you really need to make adjustments back in the studio, rather than use a technique and discover the 'hole in the middle' too late!

To a large degree, basic audio is very simple, but more difficult to capture stuff shows where the recordist's weaknesses are. Quite different to camera work where the skill level increases fairly quickly and gradually. Sound often uses almost the same processes each time until you need to use a new one and have to admit your skills are paper thin.

[Gary Nattrass]

More info here and I personally use the sony M/S ECM-MS957 mics: Recording with the Mid-Side Microphone Configuration | BH inDepth

[Paul R Johnson]

There's a Sony 979 on ebay at the moment
SONY ECM-979 Broadcast Quality CONDENSER MICROPHONE # 3 + CABLE | eBay

These are quite old now - I had one back in 1994 and they're M/S and have the width control knob, but have a left and right output, NOT M/S, so you get the benefit of the stereo capability and no hole in the middle, but lose the ability to adjust stereo width in the studio. I used one with students and they proved to be pretty tough, and sounded rather good I thought.

I think Gary's is a much newer one - but I haven't used these ones.

[Gary Nattrass]

The ones I use are the prosumer version and they are very cost effective, I also have the small ECM-MS907 as well. They both output A/B signals so you don;t have to mess around doing any matrixing but I do have an M/S width plug in for my pro tools dubbing set-up so can adjust the width later if required.

That one on e-bay is the pro version and they were used a lot by the BBC on things like wimbledon and last night of the proms if I recall correctly, they also used the ultimate M/S type mic the Calrec soundfield.

The sony's are the only stereo mic's I own and have been used to record countless stereo effects and musical items for broadcast, I have made up XLR cables for the larger one and it sounds fab just on it's own but I normally add some AT875r as spot mics as well.

[Seth Bloombaum]

Gary suggested the ECM-MS957 as a cost-effective M/S mic to me a few years ago on this forum. I've been very happy with it.

Small acoustic ensembles, single point stereo - it's good for that.
Audience ambience in larger rooms - it's good for that, too.

That's all I need a stereo mic for, and it does very well! Thanks Gary!

I too have made up 5-pin XLRF to dual 3-pin XLRM, and have run 100' or so with no problems.

[Greg Miller]

Originally Posted by Gary Nattrass

And to go back to the original question this is why as an sound pro I prefer to use an M/S stereo microphone as the forward facing capsule is always on axis to the sound source!

Yes, absolutely right! If the mic has M and S outputs, you just use M. If it's internally matrixed and you sum the L and R outputs, the side capsule will cancel out completely and you'll end up with M.

M/S has some quirks when used for stereo, but if you want a universal mic that works well in mono, then M/S is certainly preferable to X/Y.

[Gary Nattrass]

Thank you so much guys it means a lot to know I have given some good advice and helped with a mic choice!

anyone looking at a rode videomic should check out the sonys as they will be far more useful and forgiving, I use the smaller 907 as my stock interview and do it all ext mic for my canon HF11 HD minicam and have done full interviews with it as well as off cam effects and music recordings!

[Paul Wood]

I would also like to add my thanks to the contributors to this post, for a very informative lesson in the use of stereo mics - it certainly cleared up a lot of doubts on the best practices for me!

I bought a Rode NT4 last year, encouraged by a well known blogger, for use in improving interviews - one mic each for the subject, and for me, but can see now why my success has been limited!

[Gary Nattrass]

I suppose to keep it really simple we speak in mono but listen in stereo, so if you wish to record the mono human voice cleanly it is best to do it in mono, you can then post produce it for delivery into stereo if you wish.

A stereo mic has it's uses in recording stereo sounds but for recording two mono sources such as two people speaking it is best to use two mono mic's as close to the source as possible, you can then do what you wish with the recording afterwards.

[Jay Massengill]

A couple of times (over a span of 26 years) I've used a stereo mic as two mono mics to capture two people talking, however there are two important considerations to remember. The position of the two people must work well for the placement of the stereo capsules, which as Gary mentions won't be as flexible as using two individual mics that can be placed independently. Consequently you must checkerboard the audio edit to eliminate the off-axis sound from the capsule aimed at the person who isn't speaking. That's a lot of work, but sometimes the circumstances of the video shoot make two independent mics impractical.