Tuesday, December 20, 2011

Location, Location, Location

I've got a couple of challenging shows coming up that are making me rethink the old "A B" paradigm of vocal reinforcement. And that has also led me to review some of what I think I know about speaker and microphone placement.

First off, let's re-iterate; location matters. In microphones, if you put the right mic in the right place your mix will be almost done. The wrong mic in the wrong place? You mix is all but done for. In reality, of course, the position you wanted is occupied by a music stand, or the mic just isn't in inventory. And in the middle of the show the bass forgets to plug in, the tripod starts to droop, and the conductor kicks out a cable while striding to the podium. And you end up having to do horrible, horrible things with EQ just to try to eke some semblance of sound from the wrong mic that's in the wrong place.

Oh, and the one caveat is drums. Most instruments, if you picked the right mic and placed it right, it will sound good when you fire it up. You may do a little gentle EQ to taste -- or more if you are having trouble seating it in the mix. Drums are among the exceptions; there, the expected sound is an artificial construct made of very close mics with savage EQ and all sorts of funny processing (companding helps a kick a LOT). Of course, you can get a wonderful drum sound with a single overhead, or a distant pair. The book trick is to have both of your pair equidistant from the snare, as that is the loudest mid-range element and the one where phase cancellation will show up the most.

In the case of wireless microphones, the forehead at the hairline is a natural sound (slightly thin and distant, but very real sounding.) The cheek position, from ear all the way to corner of the mouth, require drastic EQ to make them sound good. They also pick up a lot more mouth noise, breath noise, and handling noise. The lapel position is almost the worst of them. Far enough down, it will be fairly natural (with a huge shadow in the EQ from the cavity under the chin) but it also shifts level with every head movement. The higher the lapel position gets, the worse it is; those women who show up in turtlenecks or high-collar blouses and try to clip to the neck line demonstrate just what happens to a poor microphone when it goes deep within the shadow of the chin. It sounds a bit like the speaker is inside a 55 gallon plastic storage drum.

The "right position" and the "right mic," of course, depends on the style of music, the style of the performer, and the needs of the mix -- whether, for instance, you are reinforcing a live band, or whether you are trying to do a recording session.

Classical violin, for instance, is best looking down from several feet above the face of the instrument. The same instrument played as a folk music fiddle is mic'd much closer. And you may chose to go more over the bow for more "hair" in the sound, or more over the bridge for a more natural tone. All of these are sculpturing decisions you make on the basis of what the musician sounds like, what the needs of the environment are, and what you have in your kit that day.

I'm about to mic a baby grand myself. I'm doing it primarily for recording, but it is before a live audience and that introduces constraints. It is set up right beside a drummer so that is a additional (large!) constraint. I am also a little unsure of the sound I want just yet; the group is oriented towards classical gospel and jazzy choral arrangements but what I heard in rehearsal from the piano was more straight-up classical piano. But with a very light hand. I look forward to seeing where she goes when she's behind the wheel of a baby grand (it could be very, very different from what I heard in rehearsal).

I'm also constrained on channels, and even more on available microphones. So I'm thinking strongly of trying a pair of small diaphragm condensers fairly tight in (I'm assuming I'll at least get the lid on long stick -- short stick will make this even harder). AT Pro37 on the right hand, about 6" back from the hammers and tipped towards the hammers as needed, and Shure PG81 (it's an SM81 at a cheaper price) over the bass strings, probably right at the cross, and tipped to almost 45 degrees towards the front of the piano. It's a variation on a scheme I've used before with some success.

I'll also get a fair amount of piano bleed in the omni condensor I'm sticking in the middle of the orchestra. And of course I have an ambient pair set up out in the audience -- a pair of old Oktava MK-012's is all I have available but at least there's a cute little ORTF bar to stick them on.

* * * *

Back from the gig. The piano mics didn't work as well as I'd hoped. It is a 5' baby grand with the lid on short stick. Not a lot of room to get in there, and the drums are right beside it. The piano sounded okay in what came through the leakage of the choral mics, though, so it isn't exactly critical to mic it for this show.

On the other hand the MK-012's on ORTF bar, up a full 12' on the sturdiest tripod I had, were very nice.

But back to location. The purpose of this blog entry is to talk about speaker location.

Speaker location for theater has two goals, goals which are largely orthogonal. The first is the "flat field"; bringing music and vocals to every member of the audience at acceptable volume and clarity. Since as FOH mixer you are basically stuck in one spot through the show, it helps the audience a great deal if most of the seats are hearing the same thing you are hearing. So you are trying very hard not to have the seats on the left hear more brass, the seats in the middle front hear more high end, and the seats in the rear of the house hear everything far too soft.

The other is placement of sounds, and for special effects particularly, what the Walter Murch coined as "Worldizing."

Take this last. To get a sound effect that sounds like it is coming from the hallway, put a speaker in the hallway. And even if you are recording; if you want a sound to sound like it happened in a bathroom, record or re-record it in a bathroom. The aim is to capture those subtle interactions that shape the perception of a space. And in the case of a theatrical setting, these subtle cues as a sound bounces around and filters out of an actual space on the stage will help make the sound believable.

Here's a simple example. Want a sound outside the windows? Don't stick a speaker facing the audience. Stick it on its back below the windows. The sound will bounce around and filter into the space.

The placement trick that started this essay, though, is in regards to vocal reinforcement.

I've had it work very well. For a production of "Master Class" I had the actress on a wireless mic for the memory sequences, and sent that to the house speakers. The sounds she remembered, of herself singing at la Scala, were played back from a pair of speakers in the wings aiming at and bouncing off a full-stage rear projection screen showing scenes from the opera house. The result was both placement, and extremely good isolation; the physical distance and the difference in sound qualities made it easy for the ear to focus on the speaker even as the singer was going all-out like only Callas can go.

The arrangement at many Broadway houses is an A-B system (or, most often, A-B-C). In the case of the pure A-B, the intention is to reduce the flanging effect of two open wireless microphones in close proximity. Thus each mic is routed to a completely different signal chain (bus, amplifier, speaker). As the show progresses actors are rotated into whichever group provides the fewest encounters.

What we do in smaller theaters is just the "C" part; the signal chain of orchestra and singer are different. Often, the orchestra is sent to a proscenium pair that provides some semblance of stereo imaging. The vocals are sent to a center cluster in mono. Again, the physical separation leverages the human ability to focus on one sound in exclusion of competing sounds, as long as there are sufficient cues to allow it to do so -- in frequency, time, or spacialization.

But the situation in a small house is not that simple. In a small house, there is direct acoustic energy from the stage. In one way this is your friend; with a little digital delay inserted into your reinforcement chain, the Haas Effect (also known as the Precedence Effect) helps the listener to localize the singer based on the first sound wave to hit them; the direct acoustic energy from the singer's mouth. If the system is set just right, you can get a good 10 dB of gain on that singer without it even being perceptible that they have a microphone (the human brain is very good at masking this sort of reinforcement from conscious perception).

The flip side is that the orchestra is also putting out direct sound, and enough to spoil any attempt towards localizing them in the house speakers. In fact, the band is putting out so much sound all by themselves you often have only a few bits and pieces in those speakers. And it gets worse if you try to ride the fader a little; all you do is change the levels of two or three instruments, throwing off the mix and the spacial placement all at the same time.

Plus, there's monitors. So another whole hunk of the volume in the audience is reflected sound from monitors, and you can't turn those down without hurting the singers and dancers ability to follow the music.

So, in the small house, your technically perfect (A/B)-C system ends up being different for every seat, and different from loud song to soft song as well.

So here's what I'm going to try over the next couple of shows. The first test case is a young cast and the band is just a small combo on stage. I'm going to eschew any band to the mains at all. I'm going to run a full band mix to monitors, but even for what would be the softer instruments -- such as electronic keyboard -- I'll provide them with band monitors so the sound level of each instrument is equal in the pit as well.

My aim is that the primary source will be either direct acoustics or the band's own monitors. Aka the orchestra itself will be the perceived source. Then I'll boost that subtly for the actors. If there is a wide dynamic range in the performance (soft solos versus large chorus numbers) I'll ride the monitor level by ear so as to raise the monitors for the benefit of the cast during the louder numbers.

The only thing the audience will hear is leakage. And there will be a lot of that, so I'm not worried on that account!

In the meantime I'll create a contoured reinforcement field using all available speakers; a mono system that is stronger towards the stage and tapers off pseudo-acoustically towards the rear of the house. With luck and tweaking I should be able to make the taper of this system similar to the taper of the band sound, thus maintaining the same mix ratio for all seats.

In the show following that, a 180 of sorts. It is going to be a loud show, rock oriented, with a semi-covered pit. I'm going to mic the orchestra and run it and the vocals hot. As a single mix; as if a rock song (the vocals will be panned center, of course.)* As much as is possible I'll run the reinforcement hot enough so it becomes a flat field out to the back of the house. The only downside to this is it will remove all localization cues from the actors themselves except for people sitting in the very front rows. Anywhere else, the actors will be heard almost entirely artificially, over the sound system. Basically I'm going to treat the place as if it was a 6,000 seat house and there was no direct stage sound.

* Stereo is a tough concept in typical theater settings. Except for a narrow aisle down the middle, most of the audience will be seated closer to one speaker than the other. Many will be so far on one side of the proscenium or the other the far speaker barely reaches them. So a hard-panned instrument or effect will be loud in one side of the audience, and unheard by the other. You can get away with this in effects, but it is murder on a mix. Imagine, if you will, half the audience hearing only the flutes and violins, the other half hearing only the brass and the cellos. Or one half hearing the right hand of the piano and the other half hearing the left.

Usually you reduce the stereo image; you avoid hard panning. If, on the other hand, you can score up a center cluster, then almost all of the audience is restored to hearing from two speakers...it is just that one will have the whole mix, the other will have only half of it. And, again, half your audience hears a different band than the other half.

The temptation arises to pan a singer as they walk across stage. Trouble is, you are reinforcing them. That is; you've already decided their voice isn't loud enough for the audience. So by choosing to pan, you are adding more volume to the audience that already had it, and reducing volume to the half of the audience that's already further away from the singer. Not good.

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